Can You Take the Heat?

Lesson Plan - Get It!

Audio:

What is heat?

Almost everything is made up of molecules that are constantly moving. This movement gives the molecules kinetic energy. The faster the molecules move, the higher the kinetic energy and the higher the temperature.

For example, if you didn't feel warm enough, what would be an easy way to heat yourself up? Add energy - run, do jumping jacks, dance...just move!

If you put energy into a system, then that system will heat up. If you take energy away, then that system will cool.

Once heat is created, it immediately wants to spread out everywhere. In other words, heat moves until temperature reaches equilibrium (all the same).

Heat = Thermal Energy = Movement of Molecules

Have you noticed that we've been talking a lot about "heat" but have not even mentioned "cold?" There's a reason for that. Heat is a thing. We can feel it, measure it, and even see it using the right equipment. This may shock you to learn, but cold is not a thing.

Now, before you start yelling about ice cubes and popsicles and winter and how cold most definitely is a thing, let's think about it. Imagine that you're holding an ice cube. Clearly it's going to feel cold, but why?

Contrary to what you might think, the ice doesn't feel cold because "the cool" leaves the ice to go to your hand. The ice cube feels cold because the heat from your hand is leaving your skin and going into the ice cube. Your hand is warm, and the ice cube is cold; so the heat moves into the ice cube in an attempt to "even out." Therefore when you "feel cold," what you're really feeling is the absence of heat.

Earlier, we said that heat is energy. But that's only partially true. Heat is a form of energy that occurs when there's a temperature difference between two things. The energy that is moving from the warm thing to the cool thing is what we refer to as heat. This is also called heat movement or heat transfer.

There are three different ways that heat transfer can occur - radiation, conduction, and convection. Use the Heat Transfer Triple Venn Diagram, found under Downloadable Resources in the right-hand sidebar, to take notes about what you learn.

When heat moves through "empty" space, we call this radiation. Heat moves via electromagnetic waves through space from the hotter to the cooler object. The most common example is solar radiation - heat traveling outward from the sun.

The sun creates energy through the process of solar fusion. This energy is then sent out in the form of heat. After a short 8 minute and 20 second trip, the solar energy (light) reaches Earth and heats up our atmosphere. For more information on this, check out the lesson under Additional Resources in the right-hand sidebar.

Conduction occurs when heat moves through a solid substance. In the image below, the heat is moving from the flame, through the solid rod, to the person's hand. The rod will quickly feel hot.

When your feet touch the hot sand at the beach, the heat moves from the solid sand to your solid feet, causing you to feel warmer. This is conduction. If you were to walk into the cool water, the heat would move from your feet to the cool water causing you to feel cooler. This is also conduction.

Where do you see conduction occurring in the image below?

When heat transfer occurs in non-solid substances, such as liquids or gases, it is referred to as convection.

As you learned earlier, molecules are always moving. Cold molecules move more slowly, causing them to huddle up and be squished together. Since hot air molecules are faster, they spread out more than the cold air molecules. This creates more empty space between the warm molecules.

Another way to say this is that warm substances are less dense and cold ones are more dense. This difference in density allows the hot substance to rise while the cold substance sinks.

Convection can occur in any gas or liquid - even molten (melted) rock. The convection under the Earth's surface is what causes its plates to slowly move. To read more about continental drift, check out the lesson under Additional Resources in the right-hand sidebar.

Now that you understand the three types of heat transfer, proceed to the Got it? section to review what you've learned.