ENERGY 23 



2. The air in the tires of bicycles left standing in the sun soon show 

 increased pressure. Why? 



3. Dough contains bubbles of carbon dioxide gas. How does the heat 

 of the oven cause the bread to rise in baking? 



4. Which is warmer, the water at the top of a water-fall or that below ? 

 Why? 



6. At the temperature of absolute zero there is no heat in a substance. 

 How would this affect the motion of the molecules? 



6. When the hand is held in the sunlight coming through a window- 

 pane, it feels warmer than the pane does. Why (28)? 



7. Why is the air cold at some distance from the earth when the heat 

 energy from the sun passes through it? - 



8. How does hammering a piece of metal affect its temperature? 



9. How does it affect the speed of its molecules? 



10. What was the source of energy which caused the changes noted 

 in the foregoing experiments? 



11. Which do you infer would warm more quickly in the sunlight, a 

 board, or the air near it? 



12. Pick out the instances of kinetic and potential energy in the fol- 

 lowing list : a coal fire, driving a nail, a rock on a mountain side, a stick 

 of dynamite, coasting down hill, a loaded gun. 



