HOW DO WE USE AIR? 



63 



Why Air in a Tire Will Support a Load. What can 

 be more useless than a flat tire ? And how different the 

 tire becomes after it is pumped up. Let us see what 

 holds the tire out after more air is forced into it. You 



laboratory pump 



bicycle pump 



Explain the movement in the valves A and B during the upstroke and the down- 

 stroke of the piston. What serves as an inlet valve in the bicycle pump ? 



remember that all matter consists of molecules in motion. 

 Study diagram 1. Here the dots represent molecules of 

 air, which are constantly moving. They bump into each 

 other and against the wall of the inner tube. As each 

 molecule hits the tube 

 it gives a push. As 

 a stream of the mole- 

 cules are pumped into 

 the tube, they are 

 squeezed in close to- 



gether and in conse- Explain what happens in a flat 

 quence more and more the tire stay up? 



why does 



