# Heat, Energy, Work, and Thermal Energy

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 system as a result of thermal contact and heat consists of random motion and the vibration of atoms, molecules, and ions.

Mini-test: HEAT, ENERGY, WORK, AND THERMAL ENERGY

Question 1: A horse pulling a car is an example of
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Question 2: Heat generally
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[divider]The following transcript is provided for your convenience.[divider]

Heat is the transfer of energy based on thermal contact, so two things have touch and energy is transferred based on temperature. Higher temperatures equal more motions, so objects and systems that are in a higher temperature are going to have more motion and more vibration in their particles where lower temperatures are going to have less motion. Heat naturally flows from hotter to colder. If you’ve 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.  It is possible to force the heat out of a colder object into a hotter object, but naturally hotter is going to flow into colder. Cold substances have motion, heat, cold substances have heat, just less than hotter substances.

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. Even though it is a cold substance sometimes whenever you feel it, it actually does still have heat in it that can be transferred.

Cold substances have heat, just less than hotter substances. They vibrate, they have motion, just less so than hotter substances.  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 hot substance, because it’s going to have less motion, it’s going to have less heat to transfer. The higher the temperature the more motion there is, the more energy there is to give away.

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 refers to energy at rest. Every substance or object is going to have a potential energy, as it starts to give off energy it becomes kinetic, but there’s still potential left in there. There is some heat source or something giving more energy to the object, it’s going to be still gaining kinetic energy, building up potential energy and giving off kinetic energy.

The energy of a specific object or substance could be changing 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 work or how much work the specific object could do.

Let’s think about a boulder going down a hill, so you have this hill and you got a boulder, well it’s got potential energy because once it starts rolling, it’s going to be giving off kinetic energy. Just sitting there it has potential, as it starts to go down its 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 it might roll back. Potential energy is just going to continue to remain there as it’s moving, it’s giving off kinetic energy. If you have someone else come in and push the boulder, then it would be receiving some more energy and have more, then it’s potential energy would g up, it’s kinetic energy would go up.

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. Energy is how much work can be done, work is the quantity of energy transferred, so they’re very closely related and they can sometimes be confusing. It’s important to work out in your mind what the difference between these two are. The quantity of the energy transferred or the amount of energy transferred 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’m 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.

I have a lot of energy into 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 my power, it’s the rate at which energy is transferred.  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 would increase.

If I started scribbling out really quickly on the board, my power would be increased. I would be having a greater quantity of 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, drink 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 is actually transferred to get a job done and power is how quickly the rate at which that energy is being transferred.

Now lets 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. 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 is being done.  If you heat an object up then it’s going to have more thermal energy.

Now that object heats itself up, then it used some work. For instance, if I’m at my normal body temperature, I’ve got a certain amount of energy available, if I go running I’m at a higher temperature. But I’ve used a lot of my energy to raise my temperature and so I actually have more available energy because work is being done. I’ve 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 have to boil water I’m doing all the action boiling the water, so the water’s thermal energy is going to increase, its going to have a higher temperature, its going to get more energy, more capacity to do work in it as it gets heated. Heat is the transfer of energy, based on temperature. Thermal energy is how much energy is available, based on some 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 needs to be transferred to get a job done. Where power is the rate at which that work is performed.