WHEEL AND AXLE 



465 



Careful experiment 

 has shown that this 

 last statement is true 

 for all machines, and 

 so it is sometimes 

 called the law of ma- 

 chines. It can be 

 stated in another 

 way : What is gained 

 in power is lost in 

 speed and what is 

 gained in speed is 

 lost in power. Notice 

 the machines you are 

 familiar with and ob- 

 serve how this law 

 holds good. All of 

 us are using different 

 kinds of levers every 

 day. Balances, scissors, nutcrackers, wheelbarrows, for- 

 ceps, and the treadle of a sewing-machine are all ex- 

 amples of levers. 



Wheel and Axle. The windlass used 

 to lift water out of a well and the cap- 

 stan of a boat are the most familiar 

 examples of this form of 

 machine. (Figure 139.) The 

 wheel and axle is simply a 

 modification of the lever. 

 (Figure 140.) The power 

 travels through the distance 

 FIGURE 139 of the circumference of one FIGURE 140 



THE LEVER AS USED BY THE ROMANS FOR 

 WEIGHING 



These scales were dug up at Pompeii and are 

 about 2000 years old. 



