What is heat energy?

EnergyEnergy 101Thermodynamics

Before we talk about heat energy, we should take a step back and think about temperature. Let’s consider that an object’s

Did you know? The faster the molecules of an object move around and bang into each other, the higher its temperature.temperature is actually a measurement of the average amount of kinetic energy its molecules have.

Remember that kinetic energy is the energy of motion, the faster something moves, the more kinetic energy it has.

“Heat energy”, or simply “heat”, is the transfer of energy from an object with a higher temperature to one with a lower temperature. This is a spontaneous process, which means that heat energy will always naturally move from a hot object to a cooler one.

Did you know? The transfer of heat from hot to cold objects happens spontaneously.

Heat can move in the other direction, from cold to hot, like in a refrigerator, but this is not spontaneous. A refrigerator keeps things cool by forcing heat out of the inside of the fridge. However, if the fridge was turned off, heat would flow into the fridge, heating up the food you are trying to keep cool. Heat energy is really all about the transfer of a certain type of energy that is associated with the motion of molecules. While the transfer of energy from hot to cold happens spontaneously, there are different ways by which heat energy can move between objects.

Did you know? Heat energy can transfer from a hot to cold object in three ways: conduction, convection and radiation.

Conduction

Have you ever heard of “firewalking”, where people walk barefoot on red hot coals? This is an interesting example of the transfer of heat. Although the coals can be extremely hot, at over 1000 degrees celsius, heat is not able to flow quickly enough to the feet of the firewalker to cause a burn. The coals turn out to be poor conductors of heat, meaning that heat transfer is a much slower process for coals than it is for a good conductor of heat, like a metal. If the firewalker decided to stop and consider this as they were walking across the coals, they would end up with a very nasty burn.

Did you know? Conduction requires objects (in this case feet and coals) to be in contact with one another in order for heat to transfer.

Convection

Heat energy transfers by convection when gas or liquid moves from one place to another because of a temperature difference. One example of this process happens when you heat a pot of water on a stove, the hot water on the bottom of the pot will rise to the top and the cooler water on top will sink to the bottom, until the cooler water heats up and the process continues, creating fluid circulation.

Radiation is different than the other two types of heat energy transfer because it does not require a solid, liquid, or gas to transfer the energy. This is how energy from the sun reaches the earth. The electromagnetic radiation from the sun, which you can think of as light rays, travels through space and some of its heat energy gets absorbed by the earth, warming it up. Without radiation transferring heat from the sun to the earth, life as we know it would not exist.

What is temperature? (HyperPhysics) Heat (HyperPhysics) Watch and Learn: Physics Professor Walks on Fire (LiveScience) Michael Shermer Firewalking Across Hot Coals (YouTube)

Michael Rogers

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• Have you ever burned yourself by touching the handle of a metal pot or pan? How could you have prevented this?
• Have you ever noticed that metal objects often feel colder than the surrounding air temperature? Describe a situation where you noticed this.
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