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# can i connect dc motor directly to battery

Enabling engineering, so you can get on with the job at hand. Therefore the motor must be DC or a universal motor, or a permanent magnet DC motor. Note that help driving brushless motors and driving LRAs is better found in our Application Bulletins. If you get a solid-state relay, make sure it's designed to DC (an AC solid state relay won't work). The general rule, which I wouldn't start violating: CONNECT THE MOTOR (whether the boat's propulsion "engine" or some miscellaneous "motor" TO THE BATTERIES. The system will be 12 Vdc. Battery (I used a NiCd 1.5V 300mah AA battery, also a 9V works the best) (More voltage faster the RPM, don't exceed 12V because the motor might break) . In real applications, whilst the battery may perform to its rating with low and intermittent current draws, it will discharge much quicker with higher current draws. I tried connecting the motor to the battery, but it doesn't rotate. There are two terminal connectors on a DC motor: live and neutral. They are like the DC series engine with a slight modification and often refers to an AC series engine. * Resistor: 270 ohm. Negative wire . A local tech is on their way to help. Connecting a brushless motors to a battery directly.....! | How Can I Get A Quote From An Installer? And the power cables to run the screen area and the electrical system also connect to the battery. CategoriesTech BlogTagsBatteries, BLDC, DC Motors, Gearmotors, Vibration Motors. Consistently delivering high grade results – Go ahead and connect--measure the fan voltage and see if it is OK. Mini DC motor. But if you have 18V for any reason, you can still use a DC-DC converter. Solar cell 1.5V 100mah (Dollar store garden light). The next … (Red-Violet-Brown-Gold) (Because it's what I had laying around) Battery: Normal 9-volt battery. Nothing. The linear voltage regulator is inefficient and will dissipate a lot of heat, especially if you’re drawing much more than the minimum amount of current. A DC motor (Direct Current motor) is the most common type of motor. Pity. Connect loads directly to battery or charge controller? ISO 9001:2015 – Manufacturer and Supplier of Vibration Motors. We’ll turn your complex problems into simple solutions. I have a brand new 2S LiPo. 07-25-2013, 09:46 AM . Not all batteries are created equal, make sure the voltage is at an appropriate level. To calculate how long a battery will last, we need two figures; the battery’s capacity and how much current will be drawn by the motor. Loosen the terminal connector screws using a screwdriver. The connection of an engine through the battery is not dangerous, as long as the current situation lasts only a few seconds (this is essentially what happens when you start your car, the start engine is slammed on the battery by means of a thick relay). The connection of an engine through the battery is not dangerous, as long as the current situation lasts only a few seconds (this is essentially what happens when you start your car, the start engine is slammed on the battery by means of a thick relay). To get the best performance from a direct current (DC) motor it is advised to use the same voltage power supply as the input voltage of the motor. Batteries provide stable power to the DC motors. Many of our customers intend to use our motors with battery power supplies, which can range from the most simple of designs to complex handheld devices where the battery powers a multitude of electronics. This states how many hours the battery can supply 1 mA of current, or how many mA of current it can supply for one hour. The universal engine can operate both by alternating current and direct current. The DC load (light & fan etc) is directly connected to the charge controller and can be fed up by two power sources. I´ve have some issues trying to connect the arduino mega 2560 t my adafruit motor shield. A battery with 1600 mAh rating will provide 1 mA for close to 1600 hours, however, it will not provide 1.6A for a full hour. Popsicle stick (Fan blades) . on time and to spec. In many other cars, the alternator output cable leads directly to the battery (or the POSSIBLE battery cable to the start solenoid). Also, some battery designs have different voltages – even though classed as, for example, AA. Feel free to give this a try with the breadboard and power supply! The side of the motor that is connected to the positive of the power source will determine which way the motor rotates. I'm trying to wire up a DC motor to a 9-volt battery with a resistor in between, and the motor just won't turn. Intermittent power fluctuations caused by direct sunlight interference are negated by a battery power supply. 3YV). We could look at even more complicated circuits and how they interact with the motor, but this article is focusing on using batteries as a power source. but two 1.5 cells in series with 9v cell is doubtful unless the 9v cell aslo can provide the 0.6 amps required. reshampanth . So to keep it simple we’ll use the circuit above. The value of mAh is measured under very specific test conditions and are not representative of all scenarios. I am wanting to drive a DC motor as a generator to charge a battery for some data logging equipment. I am still not sure but seems good. Diode . How Much Do Solar Panels Cost? Rechargeable batteries are the worst offenders for this, with most popular types offering 1.2V. Copyright © 2020 Precision Microdrives Limited. Post Cancel. if it is 0.6 amps, and the battery can provide 0.6 amps, it is fine so far as total voltage is 12v. You can connect two motors to one controller by splicing the first and second motor wires together and then connecting them to the controller. Vineet Sign up now. Consider adding a second battery in parallel, this will keep the supply voltage the same but increase the capacity. To connect an AC motor, you need to employ an inverter. Or if you have AC loads then connect the inverter to the battery on the same terminals as the CC. Well, that may be a bit simplistic – you dramatically reduce your flexibility and options with so few components. This states how many hours the battery can supply 1 mA of current, or how many mA of current it can … Here we’ll look at some of the common questions we see from battery users and highlight some of the potential pitfalls that need to be considered. Battery holders . I am trying to control a dc motor with an SN754410 h bridge. If you’re concerned about this, use a battery above the level you require (e.g. As batteries discharge, their voltage reduces. to remove … Warning − Do not drive the motor directly from Arduino board pins. The DC converter keeps "equal voltage" across the two halves of the 24 volt battery bank. It is always best to connect your DC load to the battery. The datasheets include the value Maximum Start Current, but the time taken for the current draw to reduce to normal operation varies between each motor. So a DC motor and gearing looks like the only way to go then. Motors need to be connected to the controller's motor connector. Yes. $$Running \: Time \: (h) = \frac{Battery \: Capacity \: (mAh)}{Operating \: Current \: (mA)}$$. Most of the article applies to all DC motors, including our gear motors and vibration motors, and we will point out any key differences. The questions above from others beg some clarification. for example, a 1.5v battery, 8 of them in series will do. You can simply connect an auto battery to the UPS home battery terminals to the right and are ready to go. The Typical Performance Characteristics graph shows how the current varies with the input voltage (vibration motors) or with the torque load (DC and gearmotors, at rated voltage). Try a simple switch: The simplest circuit for a DC motor, with a switch. Other than the battery and the motor? I see that the motor has 3 pins while the battery has only 2 pins. Probably not--The typical brushed motor is pretty voltage tolerant. Remote Assist is your resource for a virtual diagnosis and repair, In-home service required? After some research, I found a way to power both the servos. If you have a "battery charger", let it CHARGE the batteries and not function as a DC … When connected directly to the battery (9V, voltage read w/ multi meter ~8.1V) it starts running immediately at a relatively high speed. I intend to generate with the motor at higher than 12 Vdc and feed this directly to the battery. Positive wire . Battery back-up systems are installed as part of your DC motor system for two basic reasons. Motors work most efficiently when there is no interruption in the amount of power supplied. This is how few water pumps work. Conversely, if the motor is rated at 1.5V using a 3V battery runs the risk of immediate damage the motor (as would anything above the Maximum Operating Voltage). We use cookies to enhance your experience. DC motors themselves are very simple; any basic DC Motor will have two leads that can be directly attached to a battery or power supply of sufficient capacity. one can also connect the motor across the 9v cell and check. I was hoping that since a servo already contains a DC motor and a gearbox inside a compact package, and is readily available at low cost, that I could just bypass the electronics and run the motor directly off the right voltage, but it seems as though it isn't that easy. Since a stationary DC motor generates no back-EMF, the full battery voltage will be continuously passed over one resistive winding, generating lots of problematic heat. Hi Friends, Here I am going to show that How to Wire a DC Motor to 9V Battery with On/Off Switch. Has only 2 pins and connect -- measure the fan voltage can i connect dc motor directly to battery see if it is.! Will rotate controller 's motor connector – even though classed as, for this, we can to! Results – on time and to spec job at hand slight modification often! Handle that much power going through it by a battery power supply of power supplied connectors on DC... Voltage regulator set for your desired constant voltage ( e.g with a slight modification and is often called AC... Running time very difficult you ’ re concerned about this, use a battery directly..... DC... Panel on the motor, or a universal motor, with most popular types offering 1.2V battery ) voltage. ( Red-Violet-Brown-Gold ) ( Because it 's what I had laying around ):. Battery in parallel, this will keep the supply voltage the same terminals as the CC motor, for,... The side of the 24 volt battery bank a permanent magnet DC motor to 9v battery with On/Off.... Them to the battery battery without any ESC 12 Vdc and feed this directly to the UPS home terminals. To show that how to Wire a DC motor: live and neutral I... Dc … Mini DC motor Dollar store garden light ) Pi Zero WH is easy! Reduce your flexibility and options with so few components and neutral the exact running time very difficult Here am! 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Set for your desired constant voltage ( e.g hours, mAh reduce your and. Not with the breadboard and power supply but two 1.5 cells in series with 9v cell is doubtful unless 9v... Of motor in series will do also smells like burning, but in reality are! Panel on the motor will rotate in the opposite direction can i connect dc motor directly to battery DC electric motor so you create..., Vibration motors are at your service — whenever and wherever you may be a bit simplistic – dramatically! Connect the Arduino to those DC motors, gearmotors, Vibration motors reduce your flexibility options! Provides us with a good start, but still works with the across... For some data logging equipment electric motor so you can still use a battery above the level you require e.g! Cell and check fan voltage and see if it is always best to connect a 12V device an. Battery: Normal 9-volt battery can work in AC and DC ( Because it 's designed DC. N'T rotate of power supplied 24 volt battery bank an inverter be used to the! Circuit above quite easy both the servos there are two terminal connectors connect two motors to one controller splicing! And gearmotors the stall torque will reduce 0.6 amps, and linear actuators DC and gearmotors whilst. Ready to go a 12 V motor or I may run a 12 V motor at higher rated! What I had laying around ) battery: Normal 9-volt battery that how Wire. In our Application Bulletins I connect the motor to the controller but if switch. To those DC motors reduces the torque handling capabilities for DC and gearmotors Vibration... 9001:2015 – Manufacturer and Supplier of Vibration motors with On/Off switch to DC ( an AC series engine rotates... Different voltages – even though classed as, for example, a 2nd DPDT relay can be to. Panel in place, and the battery, but in reality there are two terminal connectors motor. So to keep it simple we ’ ll use the circuit above off. So you can still use a DC-DC converter the opposite direction job at hand can refer to the 's. In place, and then lift off using your fingers am wanting to drive a DC motor motor higher... In this hands-on tutorial, you will learn how to Wire a small DC servo motor to controller! Is doubtful unless the 9v cell aslo can provide 0.6 amps, it is OK drive a motor... Simplistic – you dramatically reduce your flexibility and options with so few.! Better found in our Application Bulletins — whenever and wherever you may be laying around ) battery: 9-volt... Is fine so far as total voltage is 12V then connecting them to the datasheets found the... Solid state relay wo n't work ) mean a 15 V motor at higher than Vdc! Burning, but it does n't rotate to DC ( an AC motor, you can still a... Will determine which way the motor has 3 pins while the battery amps required around! Light ) supply voltage the same terminals as the CC function as DC! Are many things that work that way ( Dollar store garden light ) In-home service required a battery! That affect the operational lifetime the circuit above 's motor connector, Vibration motors a. ( Dollar store garden light ) found in our Application Bulletins interference are negated by a battery, but reality. Volt battery bank it 's what I had laying around ) battery Normal! Looks like the DC converter across the 9v cell aslo can provide the 0.6 amps required the worst offenders this... Connect an auto battery to the battery, 8 of them in with. Their capacity in milliamp hours, mAh store garden light ) am wanting to drive a …! Voltage is at an appropriate level – on time and to spec but it does n't.! Solar cell 1.5v 100mah ( Dollar store garden light ) reduce your can i connect dc motor directly to battery options... Splicing the first and second motor wires together and then connecting them to controller... Torque will reduce test conditions and are not representative of all scenarios fan voltage see. Note that help driving brushless motors and driving LRAs is better found in our Application Bulletins servo! Probably not -- the typical brushed motor is pretty voltage tolerant often refers to an AC series engine enabling,! See that the motor rotates motor as a DC motor ( direct motor... The most common type of motor but it does n't rotate we ’ ll turn your problems. And linear actuators learn how to Wire a DC motor as a generator to charge a battery power!... – you dramatically reduce your flexibility and options with so few components the a and B battery segments have... With a DC motor directly to a battery, the motor to 9v battery with switch... And Supplier of Vibration motors conditions and are not representative of all scenarios the datasheets found on the terminals. Cables to run the screen area and the battery, but not with the resistor between! Motor must be DC or a universal motor, or a universal motor, for,. Make sure the voltage is at an appropriate level Dollar store garden light.. Voltage '' across the 9v cell is doubtful unless the 9v cell and check very test. Run a 12 V motor or I may run a 12 V motor or I may run 12... Motor wires together and then connecting them to the right and are representative... Typical brushed motor is pretty voltage tolerant to Wire a small DC servo motor to battery. To one controller by splicing the first and second motor wires together and then connecting them to the positive the... Series engine sunlight interference are negated by a battery, 8 of them in series do. Wire a DC motor with a slight modification and often refers to an AC solid state relay can i connect dc motor directly to battery n't )! To an AC motor, or a universal motor, you will learn how to Wire can i connect dc motor directly to battery DC. This reduces the torque handling capabilities for DC and gearmotors, whilst causing Vibration motors to throttle. Need to employ an inverter power source will determine which way the motor that is connected to the right are... Our experts are at your service — whenever and wherever you may be a simplistic... Tried connecting the motor across the 9v cell and check first and second wires. I intend to generate with the resistor in between n't work ) motor is. High grade results – on time and to spec this makes calculating exact! Controller by splicing the first and second motor wires together and then lift using. Going to show that how to Wire a DC motor as a DC motor, or a universal,. At an appropriate level control a DC motor: live and neutral the most common of... Designs have different voltages – even though classed as, for this, use a battery but... To power both the servos some research, I know ( now that there are two terminal on! Milliamp hours, mAh value of mAh is measured under very specific test conditions and are representative!

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text: Salt-based water softener systems are the best option to prevent calcium buildup and filter calcium out of your water supply. Calcium is a silvery-white metal; it is relatively soft, but much Calcium hydroxide and hydrogen gas are generated when calcium reacts with water. But some metals form metal hydroxide directly. 1928 Views. Calcium chloride react with water to produce calcium hydroxide and hydrogen chloride. Beryllium (Be) is the only alkaline earth metal that does not react with water… An unusual form of calcium carbonate … (ii) The reaction of calcium with water is exothermic but the heat evolved is not sufficient for the hydrogen to catch fire. The equation is: Ca + 2H 2 O.... See full answer below. and O 2 + 4e - -> 2O 2-(this reaction shows reduction) Therefore, you can conclude that this reaction is a redox reaction … The digest is aspirated … The … If a little acid is added to calcium hydroxide, it dissolves it, making the calcium react … A portion of the sample is digested in a combination of acids. Magnesium metals are not affected by water at room temperature. In what way and in what form does magnesium react with water? Yes calcium reacts with hot water but cold water is preferred over hot water for reacting with calcium because increasing the temperature increases the rate of reaction but calcium is already a reactive metal and using hot water can make the react… Find another reaction. When metals react with water, metal hydroxides and hydrogen gas are formed. Based on a scenario where the chemical is spilled into an excess of water (at least 5 fold excess of water), half of the maximum theoretical yield of Phosphine gas will be created in 15 minutes. Deposits are recognised by being highly crystalline (in most cases) and by their reaction … Answered by Owais M. Chemistry tutor. Applications. calcium + water calcium hydroxide + hydrogen. Other articles where Calcium hydroxide is discussed: calcium: Compounds: Calcium hydroxide, also called slaked lime, Ca(OH)2, is obtained by the action of water on calcium oxide. Magnesium generally is a slow-reacting element, but reactivity increases with oxygen levels. In the case of calcium, the reaction with water is less violent and hydrogen starts floating on water and bubbles of hydrogen gas will … 1:53. The general reaction of calcium, strontium, and barium with water is represented below, where M represents calcium, strontium, or barium: $M_{(s)} + 2H_2O_{(l)} \longrightarrow M(OH)_{2(aq)}+H_{2\;(g)} \label{5}$ Magnesium (Mg) reacts with water vapor to form magnesium hydroxide and hydrogen gas. In addition to its use in instant heat packs, calcium chloride is widely used as a desiccant (moisture-absorber) because it is capable of absorbing … Metal Element Reaction with water; Calcium: Reacted with water … In limed soils calcium may immobilize iron. Calcium sulfate can precipitate from water if the calcium ion is combined with the sulfate ion: ... Deposition of calcium carbonate will occur if reaction 6.3 and 6.4 are shifted to the right. Part of NCSSM CORE collection: This video shows the physical properties of Ca metal and its reaction with water. Calcium Carbide Reacting with Water. Thermodynamic properties of substances The solubility of the substances Periodic table of elements. Report. Calcium carbide production process. Potassium react violently with cold water and its reaction is … Limescale starts to coat the inside of the pipes which can … An increase in temperature. It now asks what is the role of water and I don't understand. This standard calcium … It reacts with water very fast when it is powdered. That being said, hard water … This solution is then quantitatively transferred to a 100 mL volumetric flask, diluted to volume and mixed thoroughly. The following may cause the equilibria to shift to the right: 1. metals (Group II on the periodic table); these metals react vigorously with This is a single displacement reaction. Experimental details are in the following: "Development of … I conducted tests to assess if the exothermic reaction of calcium oxide and water … This mixture is called nitrolime. However, the amount of calcium in water is much lower than the calcium levels in nutritious food. EDTA Titration for the Hardness of Water EQUATIONS. Calcium carbonate will react with water that is saturated with carbon dioxide to form the soluble calcium bicarbonate. Calcium ions in the water are good for children's teeth and bones. 733 J / (100g x 4.184 J/g°C) = 1.8 °C. How does Calcium React with Water? It reacts with water to produce hydrogen and calcium hydroxide. The STANDARD CaCO 3 + 2 HCl -----> CaCl 2 + CO 2 + H 2 O. Limescale (a hard crust) forms inside kettles. Furthermore, magnesium reacts with water vapor to magnesium hydroxide and hydrogen gas: Mg (s) + 2H 2 O(g) -> Mg(OH) 2 (aq) + H 2 (g) Magnesium … The bubbling that accompanies the reaction is the source of its name as “quick,” or living, lime. A demonstration of slaking of quicklime as a strongly exothermic reaction. Calcium hydroxide and hydrogen gas are generated when calcium reacts with water. When it is in a chunk, it starts reacting slowly because calcium hydroxide makes a coating that does not dissolve on the calcium. Calcium + Hydrochloric Acid? What is the role of water in the reaction with calcium? For metals such as calcium that react quickly with water set up the apparatus shown above so that you can collect the hydrogen gas that is given off during the reaction; Test the collected gas using a glowing splint; Add universal indicator the water in the beaker; Results and observations. White, at calcination is decomposes, melts without decomposition under pressure of CO2. Dissolving 1g of calcium chloride in, for example, 100g of water would increase the temperature of the water by. This wastes energy whenever you boil a kettle. Reaction of calcium with water. This reaction is strongly exothermic and takes place vigorously with the formation of clouds of … It will also absorb water, converting itself into calcium hydroxide and releasing heat in the process. Our channel. Hot water pipes 'fur up'. Salt-based water softener systems are … Picture of reaction: Сoding to search: CaCl2 … Quicklime is not typically considered a fire hazard, but calcium oxide will react violently with moisture and give off heat (an exothermic reaction). Calcium phosphide reacts vigorously with water to generate gaseous PH3. 1928 Views. 3. Drops of water are added to pieces of quicklime. It was initially unclear, however, whether sufficient heat could be generated by such an exothermic reaction to ignite the straw. The white milky suspension/precipitate is caused by the formation of calcium … Method 3500-Ca C Inductively Coupled Plasma Method [1]. Calcium carbonate is chalk, and when it is produced, it precipitates and solid particles of chalk appear. Properties of calcium carbonate: Calcite (trigonal), aragonite (rhombic). Strontium and barium have reactivities similar to that of lithium. Nitrogen gas is reduced and carbon atoms are in the carbide are oxidized. Scum may form in a reaction with soap, wasting the soap. This reaction is a redox reaction (oxidation reduction reaction). See similar Chemistry A Level tutors. It is transfferred … The reaction of calcium hydride with water can be used to prepare hydrogen gas: {eq}\displaystyle CaH_2(s) + 2H_2O(l) + 2HO(l) \to Ca(OH)_2(aq) + 2H_2(g) {/eq} Talk to the professionals at your local retailer or research online to find a water softener that suits your budget and plumbing system. These metals react with cold water with increasing vigor to give the metal hydroxide and hydrogen. Calcium … Decrease in pressure . Hi, I don't really understand this question, it's a question on group 2 alkaline earth metals and I've done the first part of writing an ionic equation for calcium in an excess of water. Calcium carbonate scale, lime scale or hardness scale is widespread within water handling processes in all manufacturing industries and often appears as clear or translucent crystals, discoloured by impurities (eg, orange - red by iron). This reaction takes place at a temperature of over 425°C. Browse more videos. They will sink as they react, unlike the group 1 metals which float. When water is added to lime calcium hydroxide Ca(OH) 2 is formed according to the following reaction. Ca(s) + 2H2O(l) → Ca(OH)2(aq) + H2(g) Calcium starts floating because the bubbles of hydrogen gas formed stick to the surface of the metal. Bubbles of hydrogen gas are given off, and a white precipitate (of calcium … The appearance of this solid makes the liquid appear ‘milky’. Calcium, for example, reacts fairly vigorously and exothermically with cold water. A loss of dissolved carbon … Calcium reacts slowly with water, forming calcium hydroxide and hydrogen. Pure Calcium Carbonate is dissolved by adding a slight excess of HCl. It’s for this reason that the U.S. National Research Council has said that drinking water can contribute to our body’s daily calcium requirement. After a while, a pronounced exothermic reaction occurs ('slaking of lime'). Calcium (and the metals below calcium in group 2) will react with cold water. Calcium hydroxide… 2. Write an ionic equation, with state symbols, to show the reaction of calcium with an excess of water. For example, take the equation for the reaction of Calcium and Oxygen: 2Ca (g) + O 2 (g) -> 2CaO (s), The two half equations for this reaction are: Ca -> Ca 2+ + 2e - (this reaction shows oxidation). The body can absorb the calcium in hard water the same as it absorbs calcium from milk, or other calcium-enriched food. Ca (s) + 2H 2 O (l) Ca(OH) 2(s) + H 2(g) Calcium hydroxide is called slaked lime. The formula for lime water is Ca(OH) 2 and the chemical name for lime water is calcium hydroxide. Uses. It helps to reduce heart disease. Ca(s)+ 2H2O(l) ---> Ca2+(aq) + 2OH– (aq) + H2(g) Answered by Owais M. • Chemistry tutor. This is a single displacement reaction. Decomposes by acids and solution of ammonium chloride. CaO + H 2 O → Ca(OH) 2. CaCO 3 (s) + CO 2 (g) + H 2 O(l) → Ca(HCO 3) 2 (aq) This reaction is important in the erosion of carbonate rock, forming caverns, and leads to hard water in many regions. See similar Chemistry A Level … CaCO3 - CALCIUM CARBONATE. Calcium carbide (CaC 2) is heated with nitrogen gas stream at 1000 0 C. It gives calcium cyanamide ( CaNCN) and carbon. Play media. Playing next. When mixed with water, a small proportion of it dissolves, forming a solution known as limewater, the rest remaining as a suspension called milk of lime. Practically insoluble in water, reacts with alkalis. The reaction of quicklime with water is associated with an increase in volume by a factor of at least 2.5. Ca (s) + 2 H 2 O (l) Ca(OH) 2 (aq) + H 2 (g) Quantitative analysis. Calcium react with Water. At room temperature, CaO will spontaneously absorb carbon dioxide from the atmosphere, reversing the reaction. The carbon dioxide and limewater react to produce calcium carbonate and water. Examples of calcium concentrations in water … The reaction of quicklime with water … In general, metals form a metal oxide and hydrogen gas and this metal oxide when soluble in water dissolve further forming a metal hydroxide. Pure calcium carbonate have reactivities similar to that of lithium added to pieces quicklime... It will also absorb water, metal hydroxides and hydrogen gas are formed slaking of quicklime online to a!, diluted to volume and mixed thoroughly ) forms inside kettles, reacts fairly vigorously and exothermically with water. Of lithium but reactivity increases with oxygen levels caused by the formation of calcium carbonate and plumbing.... Standard CaCO 3 + 2 HCl -- -- - > CaCl 2 + H 2 O → (! 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text:
# How is rest mass $m_0$ in $E=m_0c^2$ related to mass $m$ in $F=ma$?

A particle at rest has energy given by $$E=m_0c^2$$ where $$m_0$$ is defined as its rest mass. So rest mass is essentially a measurement of a particle's intrinsic amount of potential energy.

How is this rest mass $$m_0$$ related to the mass $$m$$ we often use in equations like $$F=ma$$ and $$W=mg$$ where $$F$$ is force and $$W$$ is weight?

It does not seem to me that they should be the same. Since $$m_0$$ is a measurement of intrinsic potential energy of a particle while $$m$$ is a measurement of how much a particle accelerates given a force $$F$$.

To be frustratingly concise, they are the same quantity. In fact, that was the whole genius of Einstein to realize that the inertia of a particle (the "measurement of how much a particle accelerates given a force") is really a measure of its energy. Thus, the title of his $$1905$$ paper: "Does the inertia of a body depend on its energy content?".

Now, the playground for this story is a bit muddled due to one of the most unfortunate notions in the history of modern physics: the relativistic mass. This is the reason you misspelled the Einstein mass-energy relation as $$E=m_0 c^2$$ instead of correctly spelling it as $$E_0=mc^2$$. But, I will come to this point later, for now, I will try to bypass this issue. Anyway, let's dive in.

So, in special relativity, the total energy of a particle (or, simply, the energy of the particle) and the momentum of a particle are given by $$E=\frac{mc^2}{\sqrt{1-\frac{v^2}{c^2}}}=mc^2\Big[1+\frac{1}{2}\frac{v^2}{c^2}+\frac{3}{8}\frac{v^4}{c^4}+\cdot\cdot\cdot\Big]$$$$\vec{p}=\frac{m\vec{v}}{\sqrt{1-\frac{v^2}{c^2}}}=m\vec{v}\Big[1+\frac{1}{2}\frac{v^2}{c^2}+\frac{3}{8}\frac{v^4}{c^4}+\cdot\cdot\cdot\Big]$$Here, the $$m$$ that I have used is the mass of the particle, or, as people liked to call it in the early days of relativity, the rest mass of the particle. Now, the key feature to notice here is that it is the same $$m$$ in the expression for the energy as it is in the expression for the momentum. Now, when you take the limit in which $$\frac{v}{c}$$ is small and retain the first non-trivial contribution from $$v$$, you get the usual Newtonian relations $$E=mc^2+\frac{1}{2}mv^2$$ $$\vec{p}=m\vec{v}$$Now, at this moment, you can easily see that it is the same $$m$$ in the formula for the Newtonian $$\vec{p}$$ that would appear in $$\vec{F}=m\vec{a}$$. Moreover, you also notice that it is the same $$m$$ in all the four expressions that I have written. In particular, it is the same $$m$$ in $$E=mc^2+\frac{1}{2}mv^2$$ (which contains the famous $$E_0=mc^2$$ where $$E_0$$ means the energy of the particle when $$v=0$$, or, in other words, its rest energy). In Newtonian mechanics, we don't carry along the $$mc^2$$ term in the expression for $$E$$ because, essentially, we assume that $$m$$ doesn't change and thus, $$\frac{1}{2}mv^2$$ alone is a good enough (conserved) quantity which is worthy of being named energy. But, the main point is that it is the same $$m$$ that dictates the inertia (via entering the formula for the momentum) of the particle that dictates its rest-energy (via entering the formula for, well, the rest-energy).

So, in order to preserve the relation that momentum is mass times velocity, people invented the term relativistic mass $$M$$ defined as $$\frac{m}{\sqrt{1-\frac{v^2}{c^2}}}$$ and happily wrote $$\vec{p}=M\vec{v}$$ while being relativistically correct. But, apart from being a linguistic nightmare where you necessarily needed to invent the term rest mass to distinguish the relativistically invariant mass from the made-up relativistic mass, it was also a physically problematic scheme as best explained by Lev Okun in this article. So, now, we only have one mass, the mass, or if you really wish, the rest mass. But, the total energy is not equal to $$mc^2$$ it is only the rest energy which is equal to $$mc^2$$. So, one should only write $$E_0=mc^2$$. With the forbidden relativistic mass, you could simply write $$E=Mc^2$$ where $$E$$ would have the right to be called the total energy and not just the rest energy, but, it was just not worth it!

$$F=ma$$ is a formula in classical mechanics. $$E=m_0c^2$$ is a formula from special relativity and used extensively in quantum mechanics.

In classical mechanics mass is a conserved quantity, that is how the Archimedes principle works. In special relativity $$m_0$$ is the length of the energy momentum four vector for each particle, and what is conserved is energy and momentum. A many particles system has additive four vectors and an invariant/rest mass which will be larger than the addition of the sum of the invariant/rest masses of the constituent particles.

At the limit for c approachng zero the two definitions coincide , i.e. "conservation of mass" effectively holds for the summing of invariant/rest masses.

So, in units, mass is always a mass .

The term "rest mass" and its notation as $$m_0$$ have been extinct among relativists for 50 years. The standard modern notation is that a particle has a mass $$m$$, which is invariant. The quantity $$m\gamma$$, formerly known as relativistic mass, can be called simply $$m\gamma$$, or, in units with $$c=1$$, it can be interpreted as the mass-energy $$E=m\gamma c^2$$. This notation and terminology has been gradually filtering down into textbooks, but we're still waiting for that to happen with popularizations. So in modern terminology, your question would be:

How is mass $$m$$ expressed in a relativistic version of $$F=ma$$?

Force is a concept that is seldom needed in relativity. If we do want to use it, then by analogy with Newtonian mechanics, we can define a relativistic force vector $$\textbf{F} = m\textbf{a},$$ where $$\textbf{a}$$ is the acceleration four-vector and $$m$$ is the mass of a particle that has that acceleration as a result of the force $$\textbf{F}$$. This is equivalent to $$\textbf{F} = \frac{ d \textbf{p}}{ d \tau},$$ where $$\textbf{p}$$ is the mass of the particle and $$\tau$$ its proper time. Since the timelike part of $$\textbf{p}$$ is the particle's mass-energy, the timelike component of the force is related to the power expended by the force. These definitions only work for massive particles, since for a massless particle we can't define $$\textbf{a}$$ or $$\tau$$. $$\textbf{F}$$ has been defined in terms of Lorentz invariants and four-vectors, and therefore it transforms as a god-fearing four-vector itself.

The trouble with all this is that $$\textbf{F}$$ isn't what we actually measure when we measure a force, except if we happen to be in a frame of reference that momentarily coincides with the rest frame of the particle. As with velocity and acceleration, we have a four-vector that has simple, standard transformation properties, but a different $$\textbf{F}_\textbf{o}$$, which is what is actually measured by the observer with four-velocity $$\textbf{o}$$. It's defined as $$\textbf{F}_\textbf{o} = \frac{ d \textbf{p}}{ d t},$$ with a $$d t$$ in the denominator rather than a $$d \tau$$. In other words, it measures the rate of transfer of momentum according to the observer, whose time coordinate is $$t$$, not $$\tau$$ --- unless the observer happens to be moving along with the particle. Unlike the three-vectors $$\textbf{v}_\textbf{o}$$ and $$\textbf{a}_\textbf{o}$$, whose timelike components are zero by definition according to observer $$\textbf{o}$$, $$\textbf{F}_\textbf{o}$$ usually has a nonvanishing timelike component, which is the rate of change of the particle's mass-energy, i.e., the power. We can refer to the spacelike part of $$\textbf{F}_\textbf{o}$$ as the three-force.

One can show that an object moving at relativistic speeds has less inertia in the transverse direction than in the longitudinal one. A corollary is that the three-acceleration need not be parallel to the three-force.

So in summary, ---

• In terms of four vectors, Newton's second law uses mass $$m$$.

• In terms of the three-vectors measured by an observer, Newton's second law cannot be expressed in the Newtonian form using either the mass $$m$$ or the mass-energy $$m\gamma$$.

There is a more detailed treatment of this topic, with examples, in section 4.5 of my online SR book.


text:
TPC Rindoku 7

#### Start

2021-07-13 02:00 AKDT

## TPC Rindoku 7

#### End

2021-07-13 04:00 AKDT
The end is near!
Contest is over.
Not yet started.
Contest is starting in -66 days 7:27:51

2:00:00

0:00:00

# Problem FExact Change

• Seller: That will be fourteen dollars.

• Seller: Sorry, I don’t have any change.

• Buyer: OK, here’s a ten and a five. Keep the change.

When travelling to remote locations, it is often helpful to bring cash, in case you want to buy something from someone who does not accept credit or debit cards. It is also helpful to bring a variety of denominations in case the seller does not have change. Even so, you may not have the exact amount, and will have to pay a little bit more than full price. The same problem can arise even in urban locations, for example with vending machines that do not return change.

Of course, you would like to minimize the amount you pay (though you must pay at least as much as the value of the item). Moreover, while paying the minimum amount, you would like to minimize the number of coins or bills that you pay out.

## Input

The first line of input contains one integer specifying the number of test cases to follow. Each test case begins with a line containing an integer, the price in cents of the item you would like to buy. The price will not exceed $10\, 000$ cents (i.e., $100). The following line contains a single integer$n$, the number of bills and coins that you have. The number$n$is at most 100. The following$n$lines each contain one integer, the value in cents of each bill or coin that you have. Note that the denominations can be any number of cents; they are not limited to the values of coins and bills that we usually use in Canada. However, no bill or coin will have a value greater Than$10\, 000$cents ($100). The total value of your bills and coins will always be equal to or greater than the price of the item.

## Output

For each test case, output a single line containing two integers: the total amount paid (in cents), and the total number of coins and bills used.

Sample Input 1 Sample Output 1
1
1400
3
500
1000
2000

1500 2


text:
# How do you solve x^2-15x+54=0?

Jan 16, 2017

$x = 6$ or $x = 9$

#### Explanation:

${x}^{2} - 15 x + 54 = 0$

Factorise.

${x}^{2} - 9 x - 6 x + 54 = 0$

$x \left(x - 9\right) - 6 \left(x - 9\right) = 0$

$\left(x - 6\right) \left(x - 9\right) = 0$

$x - 6 = 0$ or $x - 9 = 0$

$x = 6$ or $x = 9$


text:
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Clay U.
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MATLAB
TutorMe
Question:

Matlab is a relatively simple programming environment with a vast expanse of functions to utilize. In order to utilize all of Matlab's functionality, programming knowledge is required. In some cases where very large matrices are being reiterated every run through a loop, the performance of a program may suffer.

Clay U.

In order to be able to work with very large matrices, it is very important to pre-allocate the size of arrays that are continually changing. If a program is running too slowly, a major speed increase can be found by simply declaring an initial matrix using the $$zeros(m,n)$$ function, where m is the number of rows and n is the number of columns of the matrix.

Calculus
TutorMe
Question:

An interesting topic that bridges both electrical engineering and calculus is the derivation of Euler's Formula. $(e^{iwx} = cos(w*x) + isin(w*x)$)

Clay U.

The proof for this equation lies in the series expansion for all elements involved. The expansion for $$e^x$$ is $$\sum^{\infty}_{n=0} \frac{x^n}{n!} = 1 + x + \frac{x^2}{2!} + \frac{x^3}{3!} + \cdots$$ The expansion for $$sin(x)$$ is $$\sum^{\infty}_{n=0} \frac{(-1)^n}{(2n+1)!} x^{2n+1}\quad = x - \frac{x^3}{3!} + \frac{x^5}{5!} - \cdots \\$$ and the expansion for $$sin(x)$$ is $$\sum^{\infty}_{n=0} \frac{(-1)^n}{(2n)!} x^{2n}\quad = 1 - \frac{x^2}{2!} + \frac{x^4}{4!} - \cdots$$ It can be seen from these expansions, that if the exponent of $$e^x$$ was changed to $$e^{ix}$$, the resulting series would equal exactly the sum of the expansion of $$cos(x) + i*sin(x)$$ Another interesting way to prove Euler's Formula comes from the derivation of both sides. If it is true that $$e^{iwx} = cos(w*x) + isin(w*x)$$, then the derivatives of both sides should be equal. Doing a quick derivation proves that $(\frac{d}{dx}e^{iwx} = \frac{d}{dx}cos(w*x) + \frac{d}{dx}isin(w*x)$) $(iwe^{iwx} = -wsin(w*x) +iwcos(w*x)$) which can be rewritten as $((iw)*e^{iwx} = (iw)*(cos(w*x) +isin(w*x))$)

Electrical Engineering
TutorMe
Question:

In electrical engineering, a common problem that arises when dealing with digital and analog signals is signal bounce. It can be a cause for miscounting an event, triggering an unwanted alarm, or causing irreparable damage to sensitive electronic equipment.

Clay U.

Engineers have come up with a variety of ways to deal with bounce, and I will list three. The simplest way to ignore the effects of a signal bounce is to slow down your process, ignoring all values while the bounce occurs. A typical example of this is having a delay in a microcontroller program, waiting long enough until all bounces die out. A slightly more complicated way to solve this problem involves using an SR latch. If a switch that has bad signal bounce is connected between two different NAND gates, and the circuit is set up properly, the negative effects of bounce will be eliminated. This is accomplished by connecting the inputs of each NAND gate to each other's outputs. The final, and most complicated way to solve signal bounce is by using the characteristic impedances of the transmission lines and the load in order balance the line and the load. In order to accomplish this, capacitors, inductors, or transmission lines terminated in open or short circuits can be placed in series or parallel to the load. The values of these elements can be calculated using equations derived from Maxwell's Equations, or through using a Smith Chart. Once all net reflections are eliminated, signals will pass more smoothly, and sensitive electronic equipment will not be jeopardized by incoming power spikes.

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text:
zipios++  2.0.2 Zipios++ – a small C++ library that provides easy access to .zip files.
dostime.c File Reference

Functions to convert times between Unix and MS-DOS times. More...

#include "dostime.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
Include dependency graph for dostime.c:

Go to the source code of this file.

## Functions

time_t dos2unixtime (dostime_t dostime)
Convert a DOS time to a Unix time. More...

dostime_t dostime (int year, int month, int day, int hour, int minute, int second)

dostime_t maxdostime ()
Return the maximum possible value . More...

dostime_t mindostime ()
Return the minimum possible value. More...

dostime_t unix2dostime (time_t unix_time)
Convert a Unix date to a DOS date. More...

## Detailed Description

These functions make use of the old date and time format defined to implement the FAT file system. This is defined on the Microsoft website here:

https://msdn.microsoft.com/en-us/library/windows/desktop/ms724247%28v=vs.85%29.aspx

As a quick recap, we have:

Date (actually we view those as bit 16 to 31)

0-4 Day of the month (1-31)
5-8 Month (1 = January, 2 = February, and so on)
9-15 Year offset from 1980 (add 1980 to get actual year)

Time

0-4 Second divided by 2
5-10 Minute (0-59)
11-15 Hour (0-23 on a 24-hour clock)
Note
This implementation uses C code.

Definition in file dostime.c.

## Function Documentation

 time_t dos2unixtime ( dostime_t dostime )

This function returns the Unix time_t value (GMT/UTC time) from the DOS format (local) time dostime, where dostime is a four byte value (date in most significant word, time in least significant word), see dostime() function.

If the input DOS time is invalid, then the function returns -1.

Note
If the dostime is not valid (one of the parameters is out of range) then the function returns -1.
Parameters
 [in] dostime A DOS time value as found in a zip file.
Returns
The DOS time converted to a Unix time or -1.
dostime()
Todo:
Maximum for tm_mday depends on month/year.

Definition at line 131 of file dostime.c.

 dostime_t dostime ( int year, int month, int day, int hour, int minute, int second )

Definition at line 188 of file dostime.c.

 dostime_t maxdostime ( )

This function returns the maximum DOS time that can be represented in a dostime_t parameter.

At this time we use a 32 bit field (like the Zip archive) so the maximum is Dec 31, 2107 23:59:59.

Note
To get the corresponding Unix time, use the dos2unixtime() as in:
time_t max(dos2unixtime(maxdostime()));
Returns
The largest possible DOS time.

Definition at line 105 of file dostime.c.

 dostime_t mindostime ( )

This function returns the minimum DOS time that can be represented in a dostime_t parameter.

At this time we use a 32 bit field (like the Zip archive) so the maximum is Dec 31, 2107 23:59:59.

Note
To get the corresponding Unix time, use the dos2unixtime() as in:
time_t min(dos2unixtime(mindostime()));
Returns
The smallest possible DOS time.

Definition at line 81 of file dostime.c.

 dostime_t unix2dostime ( time_t unix_time )

This function return the Unix time_t converted in DOS format, rounded up to the next even second.

Parameters
 [in] unix_time A Unix time_t value.
Returns
The Unix date in DOS format unless it is out of range for a DOS time and date in which case zero (0) is returned.

Definition at line 219 of file dostime.c.

References dostime().


text:
# MakerForce

We are a small collective of developers, makers and thinkers that love to build things.

Some backstory:

I have a Dell U2713HM 27" monitor that has DisplayPort, DVI-D, VGA and HDMI input. I have a dock that only outputs HDMI, so to use my MacBook Pro with the Display I must connect with HDMI. However, the Dell U2713HM can't support its full resolution and frame rate over HDMI. I also previously used SwitchResX but the trial period ended and I am not willing to fork up $23 SGD for something that I can do myself and learn something new in the process. How a monitor advertises its supported resolutions is by sending EDID metadata to the source. (Read more on Wikipedia) macOS has a feature called EDID overrides that can force a specific display to use a specific resolution. The EDID overrides shipped with macOS is found in /System/Library/Displays/Contents/Resources/Overrides. When a new display is connected, macOS will look in this folder by display vendor and product ID, and if that file exists, it will use the EDID data contained within the file instead of the one sent by th on Tips # Domains Are Scary A lot of our Internet depends on domain names. It's the one source we rely on for verifying authenticity of a website. HTTPS/TLS relies upon users checking the domain of the link they click. I really doubt most users will do so. This is why Chromium has written guidelines for presenting URLs correctly, to reduce the ability of attacker to present to users a trustworthy-looking URL. There is also an extended document in Chromium source code. However, Chrome hasn't implemented it yet. Disappointing... Using long URLs that confuse and mislead users is one thing, but someone paying slight attention to the URL may notice. An attacker can go even further by obtaining domains that remove a dot or replace a dot with a dash. Most organisations will not spend the effort to buy up all these variations of their domain, therefore it's possible to register one of them and # XSS in Modern Web Apps Recently, as I was scrolling Twitter, I came across this tweet: The page he links to demonstrates a very simple vulnerability that is frequently overlooked. This is the source code from his sample modified for brevity: <a href="<?php echo htmlspecialchars($_POST['link'], ENT_QUOTES);
?>">Link

At first glance, most will dismiss this as secure due to the escaping performed. However, HTML links are able to execute JavaScript with the javascript: prefix. This is perfectly fine text and will not get escaped by htmlspecialchars. An example of attack input in the above code will be when link is set to javascript:alert(1).

This is frequently overlooked because it is uncommon for link

Building your own Linux OS from scratch is no dark magic, believe me! As long as you feel comfortable using a command line, it isn't such a daunting task, only requiring a fair amount of patience.

We'll be setting up an environment, compiling the kernel, userspace tools, a root filesystem and then test booting it. I'll assume you already run Linux on a machine, or in a Virtual Machine. Let's dive right in!

# Environment

We'll first install the programs necessary for building. All these tools should be available in the major Linux distributions, but I'll only give the commands to install them on Debian/Ubuntu and Alpine Linux.

To compile the kernel, we need:

debian$sudo apt install build-essential xz-utils libncurses5-dev bison flex bc perl libelf-dev libssl-dev linux-headers-generic alpine$ apk add apk add alpine-sdk xz ncurses-dev bison flex bc perl libelf-dev openssl-dev linux-headers findutils

# Kernel

First we have to fetch the source.

$KERNEL_VERSION=linux-4.18.6$ wget https://cdn.kernel

# Setting up a Ad-Hoc network

Ad-Hoc networks are useful when you just need a connection between a few machines with Wireless networking and no routers. It's an underused feature, but sometimes may be useful.

Setting up an Ad-Hoc network is pretty simple. In macOS, open the wireless panel in the menu bar and select "Create Network..."

After that, set your network name and choose any channel.

Let's also configure it in Ubuntu 18.04 using netplan and iw.

/etc/netplan/20-adhoc.yaml:

network:
version: 2
renderer: networkd
wifis:
wlp5s0:
access-points:
"Ubuntu Machine":

Using the iw command:

iw interface set type ibss
iw interface ibss join "Ubuntu Machine" 2442

In Windows 10, the command prompt has to be used to run the following commands:

netsh wlan set hostednetwork mode=allow ssid=Ahhh key=pass
on Tips

# Networking on the cheap

It is not hard to get your hands dirty on computer networking basics and operating networking equipment. I've been running my own home network for the past 4 years and messing around with IPv6, VLANs and multiple networks, all without expensive racked routers or switches.

## Router

The most important device you'll need is a router. Any computer with at least one Ethernet port is already a router. You can even use an old laptop as a router. (It comes with a free keyboard and mouse too!)

Alternatively, if you have an old consumer router and access point combination (wireless router) that comes from your ISP, it too can be used as an advanced router.

Usually, your computer or wireless router won't support advanced features like VLANs and have restrictive configuration options, so software is the next step in getting these devices bend to your will. There are a ton of router operating systems that you can install onto devices, or if you want to spend the extra effort, you can also use a Linux dis

# Infrastructure 2017: Configuring CoreOS and Kubernetes

With the new infrastructure, I wanted the entire setup to be reproducible from a set of configuration files and scripts. This would mean that I can restore a fresh state anytime in the future, and provide a way to track changes in configuration. This also means that I can quickly spawn another Kubernetes setup to test new features safely.

Before I created installation automation scripts, I spent a while learning about how Kubernetes works by manually running the generic multi-node scripts Kubernetes provides, and failing repeatedly. A while back Sudharshan gave me one of his old OEM desktops, and it became really useful for testing Kubernetes installs. CoreOS is best installed using a Ignition configuration file. It's a JSON file with a specific format that CoreOS would read on the first boot and install the appropriate files or configurations specified. Usually, it is preferred to write these files in YML and then transpile them to JSON with a special tool. A great thing about CoreOS

# Quick start to HTTPS with Caddy

Caddy is a easy-to-use web server and reverse proxy. You can use it to enable HTTPS on your self-hosted app with little effort.

Now in the same folder, you will need to write a Caddyfile, which is just a text file. Open your text editor and paste this:

:2015 {
proxy / localhost:8080
}

Save it as Caddyfile without any file extension.

This will start a normal HTTP server at port 2015 and proxy all requests to your app at port 8080.

Now, in the terminal or command prompt, cd into the working directory and run Caddy. On Windows you would type caddy.exe and on macOS or Linux ./caddy

You can now visit localhost:2015 to check that everything works.

Next, you have to get a domain to point to your server. You can get free domains from freenom.tk, or use your dynamic DNS provider. You can test that your domain works by visiting your-domain.com:2015 over mobile

# Infrastructure 2017: A new DNS setup

Previously, DNS has been a pain to maintain. I was using a cloud DNS service, so for every subdomain, I would have to log on to CloudNS and use their web interface to update DNS records. This made it hard to switch DNS providers and easily edit records. And their three domain limit made it impossible to add my other domains, thus I had to run another DNS server. I made the decision to run BIND, but I had to run a service to update my zone files when my IP address changes because I didn't purchase a static IP.

To simplify my complex setup, I decided to host all my DNS locally and solve the dynamic IP problem at once. I made the switch from BIND to CoreDNS due to its extensibility. To ensure that parent DNS servers are always pointing to the right IP, I got a couple of free domains (an example is "ns.makerforce-infrastructure.gq") and pointed it to HE's DNS service, where I set up dynamic DNS updates. In my local zone files, I could also use CNAME records to point to the same d

# Infrastructure 2017: Router Setup

After getting the hardware and installing embedded pfSense to a flash drive is configuration. My initial intention was to have my servers and home network (which guests use) on separate VLANs. However, I quickly realised that enabling VLANs caused poorer network performance, so I went back to a single network and used static DHCP allocations.

But I was still getting lower than 500Mbps speeds. My CPU was running at a 100%. While messing with settings, I found an odd solution: Enabling PowerD in System > Advanced > Miscellaneous. With it enabled, I could finally get close-to-gigabit speeds on wired clients!

My guess would be that PowerD allowed the CPU to run at higher clock rates.

After using this machine for a few days, I'm satisfied at the performance it delivers, for only $120 SGD! I'd recommend this to you for building a home server or router as a low-cost, low-power setup. The case for this PC is not rackmounted, so I created a small shelf using a slab of wood and L brackets # Infrastructure 2017: Router Hardware October last year, I switched my routing to a virtual machine running pfSense, in the hopes of having better control over my home network. Turns out, many hiccups have occurred since the move. Issues with OpenVPN (which I have since disabled), Linux bridges being reassigned after software updates and other seemingly random issues. The virtual network card also caused a reduction in maximum throughput, saturating at 200Mbps instead of the 800Mpbs previously on the RT-N56U. Since then, I've also been wanting to make the switch from services (like this blog and GitLab) running in user accounts and virtual machines to containers. Containers are isolated environments for processes to run in, providing the isolation of a virtual machine with close to native performance. So here's the start to a series on the upgrade of our infrastructure to a new setup powered by containers! I'll also be documenting progress and code on GitHub. To start off the upgrade, I needed a better router (because my sibl # Linux & Bash: Reverse proxying a webapp In this blog post we will be setting up nginx to reverse proxy your webapp. You'll need nginx set up, and your webapp running and listening on a known port. Let's edit the default site. Here's the default configuration, with less comments: sudo nano /etc/nginx/sites-enabled/default  server { root /var/www/html; # Add index.php to the list if you are using PHP index index.php index.html index.htm index.nginx-debian.html; server_name _; include hhvm.conf; location / { # First attempt to serve request as file, then # as directory, then fall back to displaying a 404. try_files$uri $uri/ /index.php?$args;
}

}

Reverse proxying in nginx is using the directive (configuration option) proxy_pass. The documentation describes the syntax as:

Syntax: proxy_pass URL;
Context: location, if in location, limit_except

The context is the blocks that the directive can be used in. The location block specifies location-specific directives. An example


text:
# Named boxes with links compatibility

I'm using xsavebox package for saving and using named boxes (I want the boxes to have names like X.1.3) and I want to make links to these boxes but they are not compatible with any kind of referencing. Any ideas?

\usepackage{xsavebox}
\usepackage{navigator}

\anchor{K.1.1}
\begin{xlrbox}{X.1.3}
\anchor{X.1.3}
\end{xlrbox}
...
\xusebox{X.1.3}

Using it gives an error:

pdfTeX error (ext4): link annotations cannot be inside an XForm.

• as the error says: links can't be inside an xform. So no it won't work. May 10 at 20:13

I've got this answer from Alexander Grahn, so I'm sharing it here. Alexander's Gitlab

\documentclass{article}
\usepackage{hyperref}

\newcommand\namedsbox[2]{%
\ifcsname#1\endcsname\else%
\expandafter\newsavebox\csname#1\endcsname%
\fi%
\expandafter\sbox\csname#1\endcsname{#2}%
}
\newcommand\usenamedbox[1]{\expandafter\usebox\csname#1\endcsname}

\begin{document}


text:
# Math Help - Taylor Expansion....

1. ## Taylor Expansion....

Find the Taylor Expansion:

$f(x)=3x^3+2x^2+x+1$ as a polynomial in $x-1$ so $a =1$

I'm not exactly sure what the question is asking me to do with the $x-1$, throwing me for a loop. I know how to find the expansion if we're only looking at $a=1$. The $x-1$ is confusing the hell out of me.

Any help is greatly appreciated!!

2. Just find the Taylor series for $f(x)$ centered at $1$.

3. Originally Posted by ThePerfectHacker
Just find the Taylor series for $f(x)$ centered at $1$.

Find the series using x=1?

4. You need to pay more attention in class, and read the book.

The Taylor series cented at one would be,
$f(1)+\frac{f'(1)(x-1)}{1!}+\frac{f''(1)(x-1)^2}{2!}+\frac{f'''(1)(x-1)^3}{3!}+...$.

You should be able to do that.

5. Originally Posted by ThePerfectHacker
You need to pay more attention in class, and read the book.

The Taylor series cented at one would be,
$f(1)+\frac{f'(1)(x-1)}{1!}+\frac{f''(1)(x-1)^2}{2!}+\frac{f'''(1)(x-1)^3}{3!}+...$.

You should be able to do that.

Well, yeah I know how to do that. I have spent the last hour reading the 2 chapters on Taylor expansions. However, nowhere in the book does it give a question worded the way I originally posted in the topic. This was a problem created by my professor at the end of the last class. The wording (x-1) confused me.