Energy and its Transfer
Heat, light, and sound are all forms of energy. One way that energy can be transferred is by moving atoms or molecules touching other atoms/molecules. Heat and sound can be transferred in this way. Heat will move from warmer objects to colder ones until both come to equilibrium with each other and the environment. Heat can move by conduction and convection.
Adding heat will transition substances from solids to liquids to gases. Any substance can take all three forms, although the conditions to do so are often not found in nature. The conditions (temperature and pressure) may not be able to be achieved on Earth. (Ice/water/water vapor) is a notable exception in which we often observe in all three states. Water’s boiling point changes with air pressure. The lower the air pressure, the lower the temperature that water boils at. This video clip (5:22-6:58 and 9:10 -13:44) discusses air pressure and water’s boiling point.
Conduction can happen in liquids, solids, and gasses. It requires moving atoms or molecules of one substance to come in contact with other atoms or molecules. The moving atoms/molecules move those that they come into contact with. For liquids and solids you could show what happens when a moving ball comes into contact with a group of other balls. For solids, I jumped and then touched one student’s shoulder and then had them start jumping. As soon as someone starts jumping they need to touch another person’s shoulder.
In this experiment I had the kids touch two spoons. They will feel the same, but it will be cold or warm depending on how cold their hands are. Then I had the kids put one hand on the ice and one in warm water for a bit and then feel the spoons and see that they felt different. Then I had them put one wooden spoon and one metal spoon in the warm water or the ice. When they pulled them out they could see that the wooden spoons didn’t feel very different compared to the metal ones. This was meant to illustrate that heat is transferred much quicker in some substances.
This is a way that heat is transferred in liquids and gasses. It still requires matter to touch other matter to transfer heat. Matter near the heat source heats up and becomes less dense. The less dense matter rises. As this matter rises it will start to cool down. Cooler matter then comes near the heat source. This matter heats up, and it rises. This sets up a circular pattern (convection). Here is a video clip (9:15 -11:50) that demonstrates convection.
Sound energy is also transferred by moving matter touching other moving matter. A sound can be made from an explosion or an item being hit, which starts it vibrating. This movement of the solid pushes other matter it comes into contact with. The difference is that this movement is in a wave pattern. I demonstrated this for solids by having the kids do the same as above, but instead of jumping we did a rowing motion like you would do on a crew team. You all lean forward together and back together. In air and water, the air or water is pushed so there are alternating areas of compression and areas of less dense air or water. Sound must travel through matter. It will not be transmitted in a vacuum. Sound will move differently through different materials. It travels the fastest through solids and the slowest through gasses. I showed the kids two videos about sound. One illustrates what happens to sound traveling through helium and a gas heavier than air (24:22-28:48). The second one demonstrates that you can break glass with sound waves (29:00-31:40). At the end of this class I talked about how the human ear works. The compression waves in the air push on the ear drum. The eardrum is connected to bones that strike the cochlea which is filled with fluid. The movement of the fluid moves the tiny hairs inside of the ear which sends a signal to your brain.
Heat Can Also be Transferred by Radiation
If you stick a metal object into a campfire it will heat up by conduction. The fire heats the air above it by conduction. This air rises and new cooler air comes in below (convection). However, you are warm if you sit by the side of the fire. That is because the fire is radiating heat. All hot objects radiate heat. Radiation can travel through a vacuum. This is how the heat from the sun is transferred to Earth. This will be the subject of the next class.
You can find classroom activities for heat sources here.