The GED Science test is important to prepare for. Watch the GED Science video below to see what’s on the test.
GED Science [Video Transcript]
Man: The basic tenants of cell theory are that all living things are made up of cells and that cells are the basic units of life. However, cell theory dives deeper than that. Cell theory has evolved over time and is subject to interpretation. So early cell theory was comprised of four statements, the first being all organisms are made up of cells. And so when I say organisms, that means all living things. Basically everything that lives is made up of cells. The second part of cell theory was that new cells are formed from pre-existing cells. Part three, all cells are similar, and finally, cells are the most basic units of life. So in other words, everything is made up of cells. Cells are the basic building blocks of organisms, of life.
Now some other concepts related to classic and modern cell theory includes statements such as cells provide the basic units of functionality and structure in living things. Cells are both distinct, standalone units and basic building blocks. Energy flow occurs within cells. Cells contain genetic information in the form of DNA, and all cells consist of mostly the same chemicals.
Woman: Gene mutations. Gene mutations have several different types. So one would be a missense mutations, which is where one segment of DNA is substituted for another segment of DNA which tells the gene to make a certain amino acid. And if it’s a missense mutation, then it’s telling it to make the wrong amino acid. It did code for an amino acid but the wrong one, and so this could mess up the chain. You could also have a nonsense mutation where again, a segment of DNA is substituted for the wrong segment of DNA and it doesn’t code for anything. It doesn’t code for an amino acid at all and so the chain ends there, and so it cuts that gene short and could affect the gene function.
You also have insertions which is where a segment of DNA or a base pair is inserted where it doesn’t belong and it alters the arrangement of base pairs and it could cause the chain to end early but it’s definitely going to change what the chain does and the function of that gene, that segment of DNA is going to be changed. You have deletions as well, where base pairs are just deleted and then most likely, the chain is not going to function anymore and that genetic function is going to fail.
So there are different types of genetic mutations. You can have substitutions or you just have this point substitution, this one area where a segment is changed. You can have insertions and you can have deletions. And sometimes this leads to just that one small incident and sometimes it leads to replication where there are lots and lots of mutations instead of just the one mutation.
Some causes for gene mutation are environmental causes, such as chemicals that you either ingest or that touch your body, radiation and ultraviolet lights, such as from the sun. If you have too much or sometimes just any amount of some of these things, especially chemicals, any amount of certain chemicals, and then too much radiation or ultraviolet light can make your cells mutate and it isn’t something that happens always and it isn’t something that you can say, this will specifically happen. But these are environmental causes linked to gene mutation. Biological causes would be errors made during mitosis and meiosis. And these would be something that certain mutations that might occur in a child whenever the two parents are creating the child. So when that child is forming and mitosis and meiosis are going on, any kind of hereditary mutations are going to be created in that offspring at that time. So you can have environmental causes and biological causes for these gene mutations.
And then results of the mutations. The original course of that DNA sequence is altered. So now something else is going to happen. There could be no effect. It could just end, it could not have any effect at all at that DNA chain ends and that function isn’t carried out. Maybe it wasn’t something very important and so there is no effect on the organism. It could alter the product of a gene. So the gene’s product could come out differently than it was supposed to or it could prevent the gene from functioning properly or completely. So maybe the gene’s product doesn’t get shipped out at all or it doesn’t, it ships out something that it’s not supposed to ship out or ships out part of something.
And the results can be neutral. For instance, a gene mutation in your eye color. You can have brown eyes, blue eyes, green eyes, and the mutation doesn’t harm you or benefit you generally. It’s just going to be a difference and so it will be a neutral mutation. You can have harmful mutations, such as that causes Down syndrome. You have got an extra chromosome there and that mutation causes physical and mental problems. And then you can have beneficial mutations, such as that causes sickle cell disease. And in area where sickle cell disease developed, people that had the sickle cell disease were able to fight off malaria better and so it was a survival benefit to have that mutation. So gene mutations can be caused lots of different ways and there are a lot of different types of mutations. And while most of them have little benefit or harm to us, there are some that can harm or benefit us, but genetic mutation is something that’s necessary because it’s what keeps people and or other organisms evolving and becoming more and more advanced organisms.
Binomial nomenclature. Binomial nomenclature is a formal system of naming species of living things. So it helps keep all the different species of living things organized. It’s a formal system that is used throughout the world. Each species is given a two part name based on Latin grammatical form that the words can come from other languages. Lots of them have Greek roots as well. Now the first part of the name is the genus to which the species belongs. And the second part is the species within the genus. For example, humans belong to the genus homo and the species sapiens. So we would be known as Homo sapiens. Note, how it is written as well. The whole name is written in italics.
Now, this is in normal text. If you were to have the binomial nomenclature, the formal scientific name of a species in an italicized sentence or an italicized paragraph, then you would put just this part, just the scientific name in Roman typeface to set it off from the rest of the sentence or paragraph. But in normal text, you would italicize the whole scientific name. The genus and species. And it’s written in italics with this first part, or the genus, capitalized and the second part, the species, in lowercase. And so you can see an example for any genus and species, the genus will be capitalized, the species will be lower case and the whole thing will be in italics unless there is a situation where the sentence or paragraph is already in italics and you have to set it off from the rest of the sentence or paragraph. And this binomial nomenclature, this two part naming system was thought out by Carl Linnaeus, who was a Swedish naturalist, and he formally introduced this system in 1753 and it picked up and it’s been around ever since.
Think about how many different animals and plants there are. It would be really hard to keep track of all of them throughout the whole world if there wasn’t some kind of formal naming system. And since they are based on Latin grammatical form and a lot of them have Latin roots or Greek roots, their names are going to be the same throughout the world because Latin is a dead language. It’s not going to be evolving or changing and so it’s always going to be the same. So if you have a common name for a certain creature or plant in your back yard, and someone else has a different common name for it a couple of states over, and someone else has a different name for it in another country, it will be really hard to know that you were all talking about the same plant or animal. But with this two part naming system, using binomial nomenclature, they are all going to have the same scientific name and you will be able to say, oh, I have that plant in my yard. Oh, you have got that over in that country? That’s neat. I didn’t know it was there too.
And so all over the world scientists can communicate with each other and let them know which species they found because they all are using the same formal system of naming. There is also [inaudible 00:10:58] some confusion with creatures that have the same common name. For instance a swift can be a lizard, a bird, or a fox. But if you look at the scientific name, the binomial nomenclature, the genus and species of those creatures, you will see a difference. The fox and the bird and the lizard, even though they can all be called a swift as a common name, are not going to have the same genus or species. So it’s going to be very different when you are looking at the scientific name from looking at the common name. So binomial nomenclature is this two part naming system that helps keep everyone organized and on the same page.
Man: The functions of plant and animal cells vary greatly and the functions of different cells within a single organism can also be vastly different. So we are going to take a look at plant and animal cells and the similarities and differences between them. And so first, let’s take a look at the similarities. Plant and animal cells are both eukaryotic. So they are both eukaryotic as opposed to being prokaryotic, and since them are eukaryotic, they both have a nucleus. And then a third important similarity is their reproduction process. Both plant and animal cells reproduce by duplicating genetic material, separating it and then dividing it in half. There are also some other similarities related to parts of the cells. They both have cell membranes, cytoplasm, microtubules as part of their cytoskeleton, vacuoles, and then many other structures are the same.
They both have differences with each other. And so we have plant cells and animal cells and so one huge difference is that plant cells have a cell wall. Animal cells have no cell wall. And so plant cells have a cell wall made of cellulose that can handle high levels of pressure within the cell which can occur when liquid enters a plant cell. Now, plant cells have chloroplast. And this chloroplast comes in handy in a process known as photosynthesis. So plant cells have chloroplasts that are used during the process of photosynthesis which is the conversion of sunlight into food. Chloroplasts in plants that perform photosynthesis absorb sunlight and they convert that into energy. Now, animal cells use something known as mitochondria and so the mitochondria produce energy from food in animal cells.
Another difference is that plant cells have a regular shape. In other words, they pretty much always have the same shape, while animal cells have many shapes. There are many possible shapes that an animal cell could have. And there is also a difference in size. Plant cells are larger than animal cells generally. And then finally, plant cells have cell plates and so two cells are separated by cell plates, while animal cells pinch in half. So what that means is that plant cells build a cell plate between two new cells, while animal cells make a cleavage furrow and pinch in half. So that’s not all the differences between these two types of cells but these are many of the main differences and these are many of the main similarities.
Woman: Potential and kinetic energy. Potential energy is the amount of energy an object has stored due to its position or orientation. So potential energy is how much energy an object has when it’s sitting still. It’s just stored. It is not in motion. It’s how much energy an object could have if it moved, its potential energy. And gravity, most commonly effects potential energy. There are other factors, such as mass, that can affect potential energy, but the force of gravity on an object is going to affect it the most. So if an object is up higher, it’s going to have more potential energy than an object that is down lower because the lower object is going to have a smaller amount of space to fall. The higher object is going to have a further away to fall. And so it’s going to have more potential energy.
The formula for finding potential energy, PE stands for potential energy, equals mgh. m stands for mass, g stands for acceleration of gravity. So the force that gravity is going to have on that object, and h stands for height. So you will multiply the mass of the object times the acceleration of gravity, times the height from which it is from the ground. And that is going to give you your potential energy. So you can see that the acceleration of gravity and the height, the distance an object is from the ground, are both big parts in this formula for finding potential energy. So gravity is very important to the potential energy in an object.
So potential energy is how much energy an object has stored while it’s sitting still. Kinetic energy is the energy of an object in motion. So when an object is actually moving, that is whenever you are seeing kinetic energy, and kinetic energy, KE, can be found with this formula: mv squared divided by two, where m equals the mass and v equal velocity. So mass times the velocity squared divided by two will give you the kinetic energy of an object. So this one doesn’t have as much to do with gravity because once it’s in motion, the kinetic energy has more to do with the velocity and the mass of the object.
So let’s look at this. So we have got this little situation setup. You have built this out of wood or Legos or something and you have got a ball and you are going roll it down here. So when your ball is here, you have potential energy. It’s sitting still. Once it goes over the edge, and you have it here, you have kinetic energy because this ball is in motion. If it moves down some more and sits still for a minute, you are going to have potential energy as it’s sitting still because it could still go down some more. And if it does, then you have kinetic energy again because this ball is rolling. It’s in motion. And then if it lands here, you have got potential energy again, because can still drop off this ledge. So potential energy is energy that’s stored when an object is still. Kinetic energy is the energy of motion. It’s while something is actually moving. So potential is still and stored, kinetic is moving, in motion.
Man: A neutral atom consists of an extremely dense nucleus. And so we see this nucleus right here is going to be composed of one or more positively charged protons. So I am just going to draw a circle right here and put a P in the middle. So that’s going to stand for proton. So this middle circle here represents the nucleus. It’s going to be really dense. So it’s made up of these positively charged protons. And then inside this nucleus there is also going to be a varying number of uncharged neutrons. And that exist in every atom except for hydrogen 1. So I am going to go ahead and draw some more circles and then I am going to put an N in there for neutron. And notice they are connected to the protons. Now, there is going to be a cloud of one or more negatively charged electrons outside of the nucleus. And so the number of electrons is going to be equal to the number of protons. So I am going to draw some circles with an E in them to represent electrons. So we have three protons in there. So it’s going to be three electrons.
Now say there is four protons and there is going to be four electrons out here. Now there is a bond between the protons and neutrons. They are bound together by a strong nuclear force. And so this force is stronger than the repulsive force between the positively charged protons. So all these protons are positively charged. So I’m going to put a plus symbol. And so positive charges are like charges, want to repel away from each other. But the bond between the neutrons and the protons is stronger than the repulsive force between the protons. And neutrons, by the way, have no charge. They are not positive or negative. They are uncharged. Now the negatively charged electrons, which are out here, so these are negatively charged, so I am going to put negative symbols. So these negatively charged electrons are attracted to the positively charged protons by the electromagnetic force. And so all these electrons are attracted to the protons that are inside.
Now remember earlier I said there has to be the same number of protons as there is electrons. The reason for that is because this is a neutral atom, meaning it has no charge. And so, the four positive charges that we have here cancel out the four negative charges we have. Let’s say we had four positive charges and we had seven negative charges. Overall this atom would have an overall negative charge. But that’s not the case. Because there is the same amount of positive and negative charges, the atom as a whole is neutral. Now the number of protons determines the identity of the chemical element, while the number of electrons in the outermost shell determines the ways in which the atom interacts chemically with other atoms or molecules. So this is a shell right here outside the nucleus. Sometimes, there are other shells. In this case, there is just one. And so the number of electrons in this outermost shell determines the ways in which the atom interacts chemically with other atoms or molecules.
Ionic bonds tend to form under two certain criteria. And the first is ionic bonds tend to form between metals and non-metals. So if you have two elements and one is a metal and one is a non-metal, an ionic bond is likely to form. Now the second criteria is that ionic bonds tend to form between elements with a large difference in electronegativity. So the larger the difference in electronegativity, the better the chance ionic bonds are going to form, and so if elements meet both of these criteria, there is a very good chance, they are very likely to form ionic bonds. Now keep in mind that elements with the highest electronegativity values are in the upper right hand corner of the periodic table of elements, while those with the lowest are in the lower left hand corner. So you have elements with low electronegativity down here and elements with high electronegativity up here.
And so just by knowing those two facts right there, if you see an element on the periodic table, if you just imagine this board is the periodic table, and it’s about right here, you just know by where it’s geographically situated on the board that there is a really good chance that it has a higher electronegativity because it’s near the top right hand corner of the periodic table.
Now, I have some pairs of elements here and I want to examine these elements to see if they meet these criteria and determine whether or not they are likely to form ionic bonds. So first we have nitrogen and oxygen. Now nitrogen is a non-metal. Then oxygen is obviously a non-metal. So they are not likely to form ionic bonds because it’s not between a metal and a non-metal. We have two non-metals here. Then we have potassium and fluorine, and potassium is an alkali metal. And fluorine is a non-metal. So we have met the first criteria. We have a reaction here between a metal and a non-metal. So we are doing good so far, and then there is a high electronegativity difference here. And it’s actually 3.2, which is pretty high. So they are likely to form an ionic bonds, specifically potassium chloride.
Now here we have barium and sulfur and barium is a metal and then sulfur is a non-metal. So here we have a metal, a non-metal, we are doing good so far. So they are likely to form ionic bonds, specifically barium sulfite, and then in addition to that, their electronegativity difference is moderately large, at about 1.6. Now finally, we have cesium and tin. And cesium is an alkali metal and I am sure you can guess that tin is a metal. So here we have two metals interacting with each other. So it’s not between a metal and a non-metal. So cesium and tin are not likely to form ionic bonds. So notice here the main factor here was that we had two non-metals and two metals here. But when we have a metal and a non-metal, they are likely to form ionic bonds, and especially if they have a high electronegativity difference. So hopefully through this short session, you have a better understanding of ionic bonds.
Nuclear reactions and chemical reactions have many differences, and they have one main similarity. So I am going to compare and contrast nuclear and chemical reactions. So starting off, nuclear reactions involve the nucleus of an atom. Basically a nuclear reaction is made up of a composition of a nucleus changing and so the numbers of protons and/or neutrons changes in a nuclear reaction. Now the electrons are unaffected. So while the nucleus of atoms going through a nuclear reaction are changing, the electrons orbiting the nucleus remain the same. The numbers of electrons orbiting the nucleus remain the same. And then finally, nuclear reactions can form different elements. So now we come to chemical reactions. Now as nuclear reactions involve the nucleus, chemical reactions involve electrons. Particularly, valence electrons. In chemical reactions, the atoms give, take, and share valence electrons. Now the nucleus and the rest of the atoms is unaffected. But in particular, the nucleus is unaffected.
And I want to drive home that point because up here I talked about how nuclear reactions involve a nucleus, whereas with chemical reactions, the nucleus is unaffected, instead the focus is on electrons. But with nuclear reactions the electrons are unaffected. So we have basically opposite types of reactions going on here or the ways the reactions take place are opposite. And then chemical reactions cannot form new elements or cannot form elements. But chemical reactions can form compounds. In fact, basically the product of the reaction is compounds. So those are the differences between nuclear and chemical reactions. The main similarity is how they occur. Both nuclear reactions and chemical reactions can occur spontaneously or they can occur with the addition of energy. So as you can see, we have many differences here. But they both come about in the same way, either spontaneously or with the addition of energy.
Mechanical advantage is the term used to describe how simple machines make accomplishing work easier. Now a certain amount of work is required to move an object. And the amount of work cannot be reduced. So how then does mechanical advantage reduce the amount of work you have to do when it says right here the amount of work cannot be reduced? Well mechanical advantage makes work easier by changing the way work is performed. So say for instance that you need to move an object to a given vertical height, and so a certain amount of work is required to move that object to that vertical height. Now by getting to that given height at an angle, the effort required is reduced, but the distance that must be traveled to reach the given height is increased. And so although the effort required is reduced, the length of time you have to be pushing or holding that object is increased. And so overall the amount of work stays the same. But overall, it’s easier to accomplish that work.
So a great example of this is walking up a hill. So say, we have a hill right here. If someone wants to get to the top of this hill but they are down here, they can take a direct route to the top. So it’s going to be very steep but they don’t to walk very far. But someone else could take a longer route, a meandering route, and go like this. And so as they progress up the hill, they are getting to walk up the hill at an angle. So they are only increasing an elevation slowly, much slower than the person over here who took the direct route. So it requires a lot less effort to walk here because they are not having to gain as much elevation as quickly. But the difference here is that you see how much farther they had to walk than this person because they had to go back and forth. And so even though it was easier to walk up, it took them longer. So the same amount of work is required for both of these. However, mechanical advantage is used right here by the person walking up this hill. It makes it easier overall for that person to walk up the hill.
And so there is basically six different types of simple machines that use the concept of mechanical advantage, and those are the inclined plane, the lever, the wheel and axle, the pulley, the wedge, and the screw. And so those six simple machines use mechanical advantage and those simple machines can be combined together to gain even more mechanical advantage.
Woman: Heat, energy, work, and thermal energy, these are all physics terms and it’s important to know the differences between each of these terms. Heat is the transfer of energy from a body or a system as a result of thermal contact. And heat consists of random motion and the vibration of atoms, molecules, and ions. So heat is the transfer of energy based on thermal contact. So two things have to touch and energy is transferred based on temperature. Higher temperatures equal more motion, so objects or substances, systems that are heated to a higher temperature are going to have more motion, more vibration in their particles, where lower temperatures are going to have less motion. Heat naturally flows from hotter to colder. If you have got something that is a hot substance and you mix it with a cold substance, the heat is naturally going to flow to the cold until they balance out.
But heat can be forced to move from colder substances to hotter substances using a heat pump and/or in special laboratory settings. So it is possible to force the heat out of a colder object into a hotter object but naturally, hotter is going to flow to a colder. Cold substances have motion heat. Cold substances have heat, just less than hotter substances. So for instance, if you have an ice cube and a glass of water, your glass of water could be cold water. It feels cold to you. But it still has heat in it. If you put that ice cube in the glass of water, the heat from the cold water is going to transfer to the ice cube and start to melt it. So even though it’s a cold substance sometimes, whenever you feel it, it actually does have heat in it that can be transferred. So cold substances have heat, just less than hotter substances. They vibrate, they have motion, just less so than hotter substances. So the cold water is going to be vibrating, just less than hot water would. The ice cube is going to be vibrating, just less so than the molecules in the cold water.
Colder substances have less energy to transfer than hot substances. So if you have a colder substance and a hotter substance, usually that colder substance is going to have less energy to transfer than the hotter substance because it’s going to have less motion, it’s going to have less heat to transfer. So the higher the temperature, the more motion there is, the more energy there is to give away. So now, let’s talk about energy. Energy is the capacity to do work, or a measure of how much work can be done by a substance, object, or system. Kinetic energy refers to energy in motion. Potential energy refers to energy at rest. So every substance or object is going to have a potential energy. As it starts to give off that energy, it becomes kinetic but there is still potential left in there, and if there is some heat source or something giving more energy to the object, it’s going to still be gaining kinetic energy, building up potential energy and giving off kinetic energy.
So the energy of a specific object or substance could be changing at a lot of the time. It doesn’t just stay stable. It doesn’t stay at one specific measurement of how much capacity it has to do work, how much work this specific object could do. So let’s think about a bolder going down a hill. So if you have this hill and you’ve got a boulder, well it’s got potential energy because once it starts rolling, it’s going to be giving off kinetic energy. So it’s just sitting there, it has potential. As it starts to go down, it’s still going to have potential energy because it hasn’t reached the bottom. And then once it does reach the bottom, it might start rolling up the next hill and then it might roll back. So potential energy is going to continue to remain there. As it’s moving, it’s giving off kinetic energy. If you had someone else come in and push the boulder, then it would be receiving some more energy and have more than…its potential energy would go up, its kinetic energy would go up. So energy is how much work can be done by a substance, object, or system but it is always changing. So it’s hard to nail down that exact capacity because different environmental factors, different physical factors are all going to weigh in on this capacity, this amount of work that could be done.
Now, let’s look at work. So energy is how much work can be done. Work is the quantity of energy transferred. So they are very closely related and they can sometimes be confusing, so it’s important to try to work out in your mind what the difference between these two is. So if the quantity of energy transferred or the amount of energy that must be transferred to overcome a force. For instance, lifting an object in the air, just lifting this marker requires work. Gravity is the force that must be overcome. Gravity wants this marker to lay flat on the ground. The fact that I am picking it up requires some amount of work. It requires me to transfer some of my energy to this marker and lift it up.
So work is how much energy was transferred to get this into the air. And work is measured in joules, which is abbreviated with a capital J. The rate at which work is performed is known as power. And this is basically the rate at which energy is transferred. So I have a lot of energy in my body. I have a lot of capacity to do work. When I lift this marker, I am working. I am using a certain amount of work to get this marker in the air. So the quantity that I transfer would be measured in joules and the rate at which I work is the power at which is my power. It’s the rate at which energy is transferred. So I am transferring energy slowly when I do this and when I just come up and write. But if I started raising it really quickly, my power will be increased. If I started scribbling out really quickly on the board, my power would be increased. I would be having a greater quantity energy transferred and I would be using more of my overall capacity. I would be depleting my energy. Now if I went and ate some food, drank something, then I would be increasing my capacity to do work again. So that’s where energy, the capacity to do work, can be fluid. Work is the amount that’s actually transferred to get a job done and power, is how quickly, the rate at which that energy is being transferred.
Now, let’s look at thermal energy, which has more to do with heat which we talked about before. Thermal energy is the energy present in a system due to temperature. So energy and work and power can all be influenced by temperature. The total kinetic and potential energy available due to temperature is your thermal energy. So heat is the transfer of energy as a result of thermal contact. Thermal energy is how much energy is available due to temperature. So heat is when energy is transferred due to temperature. Thermal energy is how much is available due to temperature. So it’s similar to energy, where it’s how much can be done by this object? How much is there? Thermal energy says how much is there due to temperature? And higher temperatures equal more available energy as long as no work has been done. If you heat an object up, then it’s going to have more thermal energy.
Now if that object heats itself up, then it’s used some work. For instance, if I am at my normal body temperature, I have got a certain amount of energy available. If I go running, I am at a higher temperature but I have used a lot of my energy to raise my temperature and so I don’t actually have more available energy because work has been done. I have worked my body. I’ve expended energy. Some of my energy is gone now and so raising my temperature didn’t actually give me more energy. But if I were to boil water, I am doing all the action boiling the water, so the water’s energy, thermal energy, is going to increase. It’s going to have a higher temperature. It’s going to get more energy, more capacity to do work in it as it gets heated. So heat is the transfer of energy based on temperature, thermal energy is how much energy is available based on temperature. Energy is actually the capacity to do work, how much work can be done with what that object has, and work is how much energy is transferred or how much energy needs to be transferred to get a job done, where power is the rate at which that work is performed.
Mass, weight, volume, density, and specific gravity. These are all important terms that you will find in physics and it’s important that you know the difference between each one. First, we have mass. Mass is the measure of the amount of substance in an object. So how many atoms or molecules of that one substance are in a specific object. That’s what your mass is, where weight is the measure of the gravitational pull of Earth on an object. So let’s look at our example over here. We have this rectangular prism and it measures eight centimeters long, three centimeters wide, five centimeters high. So its mass, I am just going to tell you, is 10 grams. Its weight is one pound. And in the United States, we measure weight in pounds. Other countries have different units of weight. But pretty much all of the scientific community is going to use grams and the metric system as units for mass.
So 10 grams tells us that we have got 10 grams of a substance in this box. The weight says that we have one pound of gravitational pull of Earth on that box. Now this is the gravitational pull of Earth, which means that on different planets or different entities in our solar system, the weight would be different. For instance on the moon, there is less of a gravitational pull. So your weight would be lower on the moon. On other planets that are further away or closer to the sun, you are going to have a different gravitational pull. So you are going to weigh more or less on different planets because the pull would be different. But whenever you see a weight listed, it’s going to be the gravitational pull of Earth on an object because that’s where you are most likely to find these things. Let’s move onto volume. Volume is a measure of the amount of space occupied. And there are many formulas to determine volume. It’s going to depend on what shape your object is how you are going to determine its volume. For instance the volume of a cube is the length of one side cubed, or S cubed, side cubed.
And the volume of a rectangular prism is length times width times height, or l times w times h. And in fact, that is the same formula you could use for a cube. One side times one side times one side. Just in a cube, it wouldn’t matter which side you picked, because they are all the same length. In a rectangular prism, it’s important to make sure, you take the length of a side times the length of the prism times the width of the prism times the height of the prism. You can’t just pick any three sides. The volume of an irregular shape can be determined by how much water it displaces. Let’s say you have a rock and you want to know what the volume of this rock is. How much space does it take up? Well, most of the time, a rock is not going to make a perfect sphere. So you can’t use that formula. It’s not going to make a perfect rectangular prism or cube unless it’s formed that way and ground down to be a specific size. Most of the time, you are going to find an irregularly shaped rock. So let’s look at how water displacement can help us with volume.
If you fill a beaker with some water, let’s say, we start with 20 milliliters of water, then we drop our rock into the same beaker and now our water reads 47.5 milliliters. Well, you didn’t add any more water. What you’ve added was the rock. So the difference between the new volume and the old volume is going to be the volume of your irregular object. So our rock that we dropped into the water, we can take our new volume, subtract our old volume and it’s going to tell us the volume of our rock, our irregular object. So the new volume was 47.5 milliliters. The old volume is 20 milliliters. And so we take our new volume of 47.5 minus the old of 20 and get 27.5 milliliters. So that will tell you the volume of this rock.
And there are different units of volume as well. It is not always given in the same units that width and height and length would be given in. But it can be given in more of a liquid measure since we did measure it this way. Now a milliliter is also the same as a centimeter cubed. So you could at the same time translate that to 27.5 centimeters cube. But since we did it with water displacement, I am going to leave it milliliters.
Now let’s come back to our example and find our volume. So our volume is going to be length times width times height. So let’s take this eight centimeters long times three centimeters wide times five centimeters tall. All right. Eight times 3 is 24 and then we have to multiply times 5. Five times four is 20. Five times 2 is 10, plus two is 12, and so we get 120 centimeters cubed. So whenever we multiply the centimeters out, it turned into centimeters squared and then centimeters cubed. So your answer for volume is going to be given in cubic units, so this is a 120 cubic centimeters or centimeters cubed, that is our volume of this object.
Now, let’s move onto density. Density is a measure of the amount of mass per unit volume. So then we want to know how much substance is there per the space that it makes up. So some things are going to be more dense. Their particles are going to be smashed more closely together in a smaller unit of volume, whereas some are going to be more spaced out and they are going to be in a bigger unit of volume. So density is going to tell us how much mass there is per volume, per space that an object is taking up.
So the formula for density is mass divided by volume, or d equals m divided by c. And it is given in terms of mass per cubic unit, such as grams per cubic centimeter. Grams per cubic centimeter. So let’s find the density of our object over here. So we have our mass, which is 10 grams, and we have our volume, which is a 120 cubic centimeters. So now we just have to reduce, and what we are going to end up with is being able to cross out these zeros and we are going to have 112 gram per cubic centimeter and we can turn that into a decimal because that’s usually how we like to see things. So I am going to do the division up here. So, we’ve got 8 times 12 is 96. We’ve got 4 left over, 12 goes into 43 times. So we get 36 and this is going to keep on repeating. So we are going to put another zero and come down. We are going to get 40 again. So that’s 0.083 and it’s going to repeat. So we are just going to go to three units. So our density would equal 0.083 grams per cubic centimeter. Okay. So our object has a density of 0.083 grams per cubic centimeter. That was based on its mass of 10 grams for a volume of a 120 cubic centimeters.
Next, let’s move onto specific gravity. Specific gravity is a measure of the ratio of a substance’s density compared to the density of water. So the specific gravity of a substance would be the density of the substance divided by the density of water. Now, the density of water at room temperature is 1.000 grams per cubic centimeter. If you divide anything by one, it’s going to be itself. So as long as you’re at room temperature, the specific gravity of an object is basically going to be its density. But as water gets cooler or hotter, its specific gravity is going to change a little bit. And so specific gravity can change based on air pressure, based on temperature, based on any other physical elements that are going on in the area where you are trying to determine specific gravity. So water isn’t always going to be one gram per centimeter cubed. But at room temperature it will be, and so as long as everything is at room temperature, regular pressure, then you are going to have your specific gravity be basically the same as your density of the substance.
Now, if your specific gravity is greater than that of water, so it’s greater than one gram per centimeter cubed, then your substance is going to sink. It’s denser than water. It’s going to sink below the water. If your specific gravity is less than water, then your substance will float. It has a specific gravity that’s less than water. It is less dense than the water. So it’s going to float. For instance, if you put most metal, if you put a penny in water, it’s going to sink because it has a higher specific gravity than water. But if you have a piece of wood, it’s usually going to float because it’s going to have a lower specific gravity than water. If the specific gravity of a substance is one or right at one, then it will be buoyant. So it will kind of bob around the top of the water. It won’t float right above it, it won’t sink to the bottom. It will bob right around the top.
So let’s look at the specific gravity of our box over here. So we’ve got our density of the substance, which is 0.083 grams per cubic centimeter. And we have water, which is 1.000 grams per cubic centimeter. So your specific gravity would just be 0.083 grams per centimeter cubed because at room temperature water is going to be one and dividing by one is going to get you the same thing. So would this one, our box here, would it sink or float? Is the specific gravity less than that of water or greater than that of water? It’s less than that of water. Less than specific gravity of water. So when it’s less than that of water, it’s going to float.
So let’s review all of these terms to make sure we understand the difference. The mass of our box was how much substance was in there. We had 10 grams of a substance in this shape. It weighed one pound. That was how much gravitational pull Earth had on the object. Its volume was based on its actual size, how much space it occupied, and it came out to 120 centimeters cubed and we got that by multiplying length by width by height. Its density was mass divided by volume. So our mass of 10 grams divided by volume of a 120 centimeters, and we rounded that to 0.083 grams per centimeter cubed because we were going to keep repeating forever with that 3.
And then the specific gravity was just 0.083 grams per cubic centimeter as well because at room temperature water is one gram per centimeter cubed as well and the density isn’t going to change very much, and the specific gravity is just going to be the same as the density. Since our object’s specific gravity was less than that of water, we know that it will float.