Heat energy is constantly being transferred from one substance to another. Heat energy always moves from the hotter material to the colder material. When you hold an ice cube, it might feel like the coldness is creeping up your hand, but it’s actually the other way around—the heat of your body transfers to the ice cube, which results in the ice cube obtaining a higher temperature and eventually melting.
Conduction is the most efficient form of heat transfer. In conduction, molecules of the warmer substance are moving faster than the molecules of the cooler substance. When the faster moving molecules collide with the slower moving molecules of the cooler substance, some of energy of the warmer substance is passed on. The cooler molecules that were directly collided with are moving faster, and when they collide with the surrounding cool molecules, they start moving faster too. Conduction is kind of like the game “telephone,” where the message is passed on by every individual in the circle.
The speed of conduction depends on how different the temperatures of the two objects are, how far apart they are, and what type of materials are conducting the heat. For instance, metal is a far better conductor than Styrofoam. That’s why metal is used for cooking and Styrofoam is used for the disposable coffee cups.
- Refrigerated butter or margarine
- Long metal spoon
- Pony beads
- Large glass Jar
- Hot tap water
- Using tiny bits of cold butter, secure the three beads to the spoon handle. Make a hypothesis as to which bead will fall off the spoon first.
- Have a grown-up fill the jar with enough hot water so that just the bowl of the spoon is submerged.
- Place the spoon in the water, set the timer, and watch.
You are likely to see bead A drop off first, then bead B, and then bead C. The time it takes to do this depends on how warm your water is, and the type of butter and spoon you used.
Remember that conduction involves direct collisions between the molecules. For your particular heat transfer experiment, the source of the heat energy is the warm water. The molecules of the warm water first collide with the metal molecules in the bowl of the spoon. The molecules in the bowl of the spoon are moving faster, and they are closest to the molecules in the lowest part of the handle, so that is the next place the heat energy is transferred. The first of part of handle to get the conducted heat energy is under bead A, so the butter under that bead softened, and the bead fell off. The heat energy continued travelling along the spoon, reaching the butter under bead B next and bead C.