Page:Model steam turbines; how to design and build them (IA modelsteamturbin00harrrich).pdf/13

Rh It is necessary here to distinguish carefully between mere velocity or speed, and acceleration or increase in velocity.

Supposing a body travels 100 feet in five second, its average velocity is evidently $100/5$=20 feet per second, or


 * V=$s/t$ .  .  .  .  .  .  (3)

where V is the average velocity in feet per second, s is the distance covered, and t the time taken in traversing s.

If the body started from rest under the action of a constant force of such magnitude that its velocity increased at the rate of 20 feet per second in each second, its successive velocities at the end of the 1st, 2nd, 3rd, 4th, and 5th seconds would be 20, 40, 60, 80, and 100 feet per second. Since its initial velocity was zero, and the velocity at the end of five seconds 100, the average velocity is given by

$0+100/2$ = 50 feet.

From (3) we see that the distance travelled is equal to velocity × time, and as V is obtained by dividing the final velocity by 2, the distance traversed by a body not moving at a constant velocity as in (3), but at a uniformly increasing one, is equal to Final velocity at any instant × time 2 or from which