FORCE AND MOVING BODIES 177 



7. When a car in which we are riding stops suddenly, we are thrown 

 forward. Why? 



8. In what direction are we thrown when a car starts suddenly ? Why ? 



9. In carrying a glass full of water, why is it likely to spill if we stop 

 suddenly? 



10. Lay a small card over the mouth of a drinking glass and put a coin 

 on the card. Drive the card away horizontally by a smart snap of the 

 finger and explain the action of the coin. 



11. Place a penny on a cloth-covered table and invert over it a drink- 

 ing glass propped up by three larger coins. By scratching on the cloth 

 near the penny, it may be made to creep out from under the glass. 

 Explain. 



12. Why is one likely to be thrown down when jumping from a rapidly 

 moving vehicle? 



13. Why, in jumping from a small boat, does the boat move away as 

 we jump? 



14. How is it possible to drive a nail by striking it with a hammer? 



15. When one cracks an egg by striking it against a hard object, is it 

 action or reaction that breaks the shell? 



16. Mud which will stick to a slowly revolving wheel will be thrown 

 off when the wheel moves faster. Why? 



17. Grindstones, emery wheels, and the like are sometimes turned so 

 fast that they break. Why? 



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