2. THERMAL EXPANSION Friday, February 24, 2012

3. Thermal Expansion Particles move more when they get hot. When the particles move more, they spread out. When the particles spread out, the matter they are part of expands. BIG IDEA: When things get hotter, they get bigger (in most cases).

4. Thermal Expansion The cracks that we see in the streets and sidewalks are caused by the thermal expansion and contraction created by our hot summers and cold winters.

5. Thermal Expansion Bridges, roads, and sidewalks are built with ‘joints’ so they don’t crack when the temperature changes.

6. What does all this have to do with the balloons? Now that you have a basic understanding of thermal expansion, write a hypothesis that explains what you saw in the balloon demonstration. When the bottle is placed in the cold water, the air inside the bottle cools and contracts (gets smaller and takes up less room), causing outside air to be drawn in, pulling the balloon in and inflating it inside the bottle.

7. Bring it Back to DENSITY!!! So if an object expands when it gets hotter, will it become more or less dense? LESS DENSE

8. Hey Wait! Ms. Grom wants to see if you’ve got this! Use your understanding of thermal expansion to explain how a hot air balloon works.