1. Journal 3/14/16 What do you think causes cracks in the sidewalk and road? Objective Tonight’s Homework To learn how heat causes objects to expand p 383: review 3, WDYL 3 p 382: review 8

2. Heat Expansion and Insulation Look at a sidewalk. You’ll notice the concrete has been divided into blocks. Why?

3. Heat Expansion and Insulation Look at a sidewalk. You’ll notice the concrete has been divided into blocks. Why? If you compare summer to winter, the answer becomes obvious. The gap or groove between blocks is much smaller in summer than in winter.

4. Heat Expansion and Insulation You’ll see this same effect in other objects as well. Does anyone have a house door that has trouble closing in the middle of summer? Or a ring that doesn’t fit as well in summer? All these things are examples of what we call heat expansion. So our next question follows naturally: Why do things physically expand bigger in heat?

5. Heat Expansion and Insulation Everything is made of atoms. As we increase the temperature of an object, the atoms it is made of move faster and push apart more.

6. Heat Expansion and Insulation Let’s jump back to conduction, convection, and radiation. We said that some materials transfer heat better than others. Metals are excellent conductors. Wool, wood, brick, and glass are poor conductors – insulators.

7. Heat Expansion and Insulation If you touch a piece of metal that’s been sitting in a room for a while, the metal will still feel colder than the room around it. Why? Because as soon as you touch the metal, heat starts flowing from your hand into the metal, cooling your hand.

8. Heat Expansion and Insulation Insulators come in many forms (especially for homes), but all of them are designed to stop heat from flowing out of a house in winter and to stop heat from flowing into a house in summer. Coats and blankets are also insulators, designed to trap heat from your body and keep it next to your skin. They don’t keep the cold out, they keep the heat in!

9. Insulation Lab Tomorrow we’re going to do a simple lab. Mr. C. is going to take a beaker and put a few marshmallows in the bottom. He’s then going to take this beaker and put it about 6 inches above a hot plate that will be turned on. Your job (with a partner) is to come up with some kind of insulation or conduction that will keep the marshmallows from melting. You have the rest of the class to brainstorm how you’ll do this. You need to bring materials (probably disposable) from home to class tomorrow. If you don’t bring stuff, you automatically get a zero! Hot plate

10. Exit Question Most computers have something inside them called a “heat sink” which is designed to quickly get heat away from the computer and out into the outside air. What material do you think most heat sinks are made from? Wood Metal Glass Ceramic (similar to brick. Sort of) Nylon (a synthetic fabric) Magic