# Tagged Questions

General questions about the way objects move and interact. This tag should be used when the tags for certain kinds of mechanics (newtonian-mechanics, classical-mechanics, quantum-mechanics, etc.) are too specific.

1answer
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### How large of a solar sail would be needed to travel to mars in under a year?

I'm attempting to approach this using the identity $$F/A = I/c$$ I can solve for Area easily enough $$A = F(c/I)$$ and I know the distance $d$ is $$d=1/2(at^2)$$ But I'm having difficulty trying to ...
0answers
19 views

### Ignoring rotational inertia of a ballistic pendulum

When calculating the initial velocity of a steel ball by using a ballistic pendulum, but by ignoring the rotational inertia of the pendulum rod, a systematic error is introduced. My question is will ...
1answer
62 views

### Calculating how a polygon bounces off a plane

I'd like to calculate how polygons bounce off a plane. In this picture, the square doesn't bounce straight up, but instead it bounces somewhat to the right and starts spinning. But I have no idea ...
0answers
6 views

### Finite Element, NASTRAN, how to print the differential stiffness matrix in .f06 output file [migrated]

We are working on an optimization problem in which we can approximate the eigenvalue calculation by assuming a constant eigenvector, using the formula:  ...
0answers
15 views

### Row of pivoted magnets and energy scale

This question is about a system involving a horizontal row of length L of equally spaced pivotable magnets, each with a pole at either end. These magnets will often be referred to as units. So each ...
1answer
34 views

### What lifting mechanism is likely to have the best energy recovery ratio?

Suppose I was designing an apparatus which needed to lift 250kg 5cm high, hold it there for a few seconds, and then lower the object back to the original height. Such a process would need to be ...
2answers
63 views

### Hamiltonian of Harmonic Oscillator with Spin Term

We have the usual Hamiltonian for the 1D Harmonic Oscillator: $\hat{H_{0}}=\frac{\hat{P^2}}{2m} + \frac{1}{2}m \omega \hat{X^2}$ Now a new term has been added to the Hamiltonian, \$\hat{H} = ...
1answer
27 views

### Terminal velocity and force pull [closed]

I can't figure out this problem . Buoyancy force and gravity remain constant and viscous force by is $-kv$. And these forces all balance, but data isn't given according to that, or I am not able to ...
1answer
47 views

### Floating Objects and Weight

The Situation: A ball is placed in a beaker filled with water and floats. It is also attached to the bottom of the beaker via a string. The Question: The ball is attached to the beaker, thus ...
1answer
35 views

### Finding the coffecient of restitution

A ball moving with velocity $1 \hat i \ ms^{-1}$ and collides with a friction less wall, afetr collision the velocity of ball becomes $1/2 \hat j \ ms^{-1}$. Find the coefficient of restitution ...
0answers
72 views

### How to calculate mechanical advantage of a worm gear?

How to calculate mechanical advantage of a worm gear? My textbook simply use the turn ratio as the mechanical advantage, but I'm not sure how that works. My thinking: If the worm has a radius of ...
1answer
86 views

### Confusions about rotational dynamics and centripetal force

I am a high school student. I am having confusions about the centripetal force and rotational motion . I have known that a body will be in rest or in uniform velocity if any force is not applied. But ...
1answer
59 views

### A sphere rolling down a rough wedge which lying on a smooth surface

A sphere of mass $m$ and radius $r$ rolls down from rest on an inclined (making an angle $\phi$ with the horizontal ) and rough surface of a wedge of mass $M$ which stays on a smooth horizontal floor. ...
1answer
135 views

### Mechanics question

The following is a question from a past exam paper that I'm working on, as I have an exam coming soon. I would appreciate any help. A fairground ride takes the form of a hollow, cylinder of radius ...
3answers
148 views

### Does more rain strike a vehicle while moving or while stopped (or neither)? [duplicate]

Assume there is a rainstorm, and the rain falling over the entire subject area is perfectly, uniformly distributed. Now assume there are two identical cars in this area. One is standing still, and ...
4answers
77 views

### Would a phone move upon vibration in a completely uniform situation?

I was sitting down yesterday and saw my phone vibrate on a side, and it moved about a centimetre per vibration. I wondered why it moves, and thought perhaps that the side it was on had a slight ...
0answers
51 views

### Scaling arguments for the Contact mechanics between two elastic spheres

I am studying a bit granular dynamics and I have seen that two spheres of radius $R$ in contact with a contact area of radius $a$ would need an applied force $F$ on this two spheres that is nonlinear ...
3answers
63 views

### Friction on roads

I have a question with which I am having trouble. A 71m radius curve is banked for a design speed of 91km/h. Given a coefficient of static friction of 0.32, what is the range of speeds in which a car ...
2answers
112 views

### Whats the anti-torque mechanism in horizontal take-off aircraft?

In most helicopters there is the anti-torque tail rotor to prevent the body from spinning in the opposite direction to the main rotor. What's the equivalent mechanism in horizontal takeoff single ...
1answer
52 views

### Hollow stone columns provide more support?

In history class in elementary school I remember learning that the Greeks would build their stone columns hollow because they thought this provided more support. Is it true that a hollow column is ...
1answer
44 views

### Measuring vibration and converting to force (N)

The test is: To have a rotating machine, bolted into a factory floor. To measure the vibration on 3 axis (output of accelerometers can be acceleration or velocity in $\mathrm{m/s}$ or ...
1answer
82 views

### Shear Flow corresponding to Eccentric Shear Force of a Closed-section Beam (Structural Analysis - Mechanics)

Been stumped with this question for way too long... its a beam with a thin-walled rectangular cross-section, and a shear force is acting at a distance from the shear center. I know my decomposition of ...
1answer
82 views

### (Re-)use of a space elevator (basic mechanics and potential energy source)

It's said that if a space elevator were made then it would be much more efficient to put objects in orbit. I've always wondered about the durability of a space elevator though. I don't mean the ...
1answer
29 views

### Mechanical shock resistance as a function of shape

I have a system where I'm dropping glass tubes filled with some sample from a certain height, along a track. I can apply a back-pressure of air to push them down faster, and in general the faster they ...
2answers
101 views

### How do you tell what forces do no work?

The total mass of the children and the toboggan is 66 kg. The force the parent exerts is 58 N (18 degrees above the horizontal). What 3 forces/ components do no work on the toboggan? I said the ...
1answer
102 views

### Intuition behind Work

I have a doubt in understanding the intuition behind the concept of work. First of all, I think this isn't duplicate, I've searched on the site, and the closest thing I've found was this post which is ...
2answers
144 views

### Universe Expansion and two tennis balls

Clear the universe of all matter except for two tennis balls. Place the two tennis balls in the same inertial frame 1 Mpc apart. Are the tennis balls getting further apart? Will the tennis balls ...
0answers
119 views

### Maximum Shear on a Beam - beam with fixed support on one end and hinge on other end

A beam $\displaystyle 3m$ long with fixed support on one end and hinge on the other end is subjected to a uniform load of $10\ kN/m$. What is the maximum shear of this beam? The solution is this one: ...
2answers
145 views

### Cantilever Beam - Maximum Shear of the Beam

A cantilever beam $3\ \text{m}$ long is subjected to a moment of $10\ \text{kNm}$ at the free end. Find the maximum shear of the beam. The answer is "There is no vertical load, shear is zero" ...
1answer
79 views

### Finding the acceleration of a cart rolling on a table

The cart is rolls frictionless on the table. It has a mass of $1 kg$. Attached to it are 2 strings, that go through two frictionless sheaves. The weights have masses as in the picture. ...
1answer
65 views

### Why is $dL = L d\epsilon$?

Let's say there's a random elastic material. It's length is $L$ and it's tensile strain $\epsilon= (L-L_0)/L_0$ Now, when one pulls on it the following is true: \$dW_{tot}=FdL =\sigma AdL=\sigma A L ...
1answer
153 views

### Drag on a spinning ball in fluid

I am a physics newbie (high school level) and I am wondering what happens when a spherical object is spinning on the spot in a bunch of gas (no gravity here, just an imaginary physics sandbox). Am I ...
1answer
65 views

### Atomic physics through classical resonance?

I have a rather general question regarding the theory of Quantum Mechanics. To preface this question, consider a violin string. When a violinist exposes the string to a bow, this is exposing the ...
2answers
69 views

### What fraction of peak horsepower do typical 4 door passenger vehicles use?

I was surprised when I looked at the power rating of the engine used on a Humvee. It's only ~190 horsepower, which is exceeded by many sedan engines. So an obvious question is why doesn't my Camry SE ...
1answer
63 views

### Lego Blender and gear ratios

I bought the Lego Kit LEGO Crazy Contraptions. It allows the learner to build a blender. My son, the engineer, said something to our grandson, his son, about a gear ratio. Can someone translate?
4answers
203 views

### Pseudo force in rotating frames

A bug of mass $m$ crawls out along a radial scratch of a phonographic disc rotating at $\omega$ angular velocity. It travels with constant velocity $v$ with respect to the disc. What are the forces ...
2answers
115 views

### distance of electron from proton

An electron is projected, with an initial speed of $1.10 \times 10^5 \text{m/s}$, directly towards a proton that is essentially at rest. If the electron is initially a great distance from the ...
0answers
17 views

### Allowed Quantum States- Filkelstein and Rubinstein constraints

So basically i'm doing a report on Finkelstein and Rubinstein constraints. I have a system where the allowed quantum states satisfy ...
2answers
176 views

### Why is the Lagrangian quadratic in $\dot{q}$? [duplicate]

My teacher said we only consider Lagrangians which are quadratic in $\dot{q}$, and we don't take other Lagrangians. I couldn't understand why. Can anyone please explain this?
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89 views

### Internal moment in the hull of a pressure vessel

This question is related to the course structural analysis. As part of our exam grade every student has been given different multiple homework assignments which we have to solve. One of the problems ...
0answers
59 views

### Limitations on the choice of axis of rotation regarding rolling wheels

Consider a situation where a wheel is rolling without friction on a level surface. Call the center of the wheel $C$, the point where the wheel contacts the ground $G$, and some arbitrary other point ...
4answers
317 views

### Difference between torque and moment

What is the difference between torque and moment? I would like to see mathematical definitions for both quantities. I also do not prefer definitions like "It is the tendancy..../It is a measure of ...
2answers
73 views

### How can I understand work conceptually?

I'm in a mechanical physics class, and I'm having a hard time understanding what the quantity of work represents. How can I understand it conceptually?
0answers
59 views

### Fluid flow in a hollow spring(helix)

Liquid flowing in a long hollow spring(helix). Any effects on the flow rate etc when the spring is stretched or compressed? When the stretching or compressing of spring is done at brisk speeds the ...
2answers
144 views

### Is there any case in physics where the equations of motion depend on high time derivatives of the position?

For example if the force on a particle is of the form $\mathbf F = \mathbf F(\mathbf r, \dot{\mathbf r}, \ddot{\mathbf r}, \dddot{\mathbf r})$, then the equation of motion would be a third order ...
1answer
94 views

### How much (usable) potential energy is stored in a compound bow?

I have done a bit of reading about the energy stored in bows, but I haven't seen anywhere a description of how much energy actually is stored. Clearly there are many factors, bow design being ...
2answers
140 views

### Total Mechanical Advantage

How do you find the net Mechanical Advantage (MA) of two joint machines. Do you add or multiply the individual MA? Suppose I have two sets of wheel and axle connected by a fixed pulley. Each of the ...
1answer
49 views

### In which direction is the acceleration directed in a non uniform circular motion?

Acceleration is directed towards the center of the circle in a uniform circular motion. Is it same for the non-uniform circular motion?
2answers
222 views

### Translation Invariance without Momentum Conservation?

Instead of the actual gravitational force, in which the two masses enter symmetrically, consider something like $$\vec F_{ab} = G\frac{m_a m_b^2}{|\vec r_a - \vec r_b|^2}\hat r_{ab}$$ where \$\vec ...
0answers
47 views

### Fading transition and rotation of and object in 2D

I'm looking for sources about I guess dynamics subject. The model I'd like to solve is reduced to a question of: How does a force applied on a certain point of an object results in both fading ...
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