PROPERTIES OF MATTER 



43 



FIGURE 14 



In the experiment with the air compressor we found that 

 the space occupied by the air could be reduced only to a 

 limited extent. Greater force might have compressed the air 

 into smaller space, but no amount 

 of force could reduce the air to a 

 point where it did not occupy at 

 least some space. When we pump 

 up a bicycle tire, we see again that 

 air demands room for itself. These 

 examples illustrate the truth that 

 all matter occupies room or space. This property of matter 

 we call extension. 



Experiment 10. Place a coin on a smooth card extending 

 slightly beyond the edge of a table. (Figure 15.) Suddenly snap 

 the card horizontally. Does the coin move? 



When the card was snapped from under the coin, the coin 

 moved very slightly, if at all. The force of the finger was 



applied only to the card, and 

 the card was so smooth that it 

 did not convey any appreciable 

 motion to the coin. If the coin 

 had been glued to the card, both 

 coin and card would have moved. 

 This illustrates the truth that a body at rest does not 

 begin to move unless some force acts upon it. 



Experiment 11. Revolve around the hand a small weight at- 

 tached to a strong rubber band. Suddenly let go the band. Does 

 the weight keep on moving in the circular path in which it was 

 revolving? 



When we let go the band, the weight started off in a 

 straight line. (Figure 16.) It did not continue in a straight 



FIGURE 15 



