Page:Model steam turbines; how to design and build them (IA modelsteamturbin00harrrich).pdf/11

. (according to its magnitude), may be measured by the velocity generated in one second on a body free to move in any direction whatever. Unit force is that force which, acting on a free body of one pound weight, generates in it a velocity of one foot per second. In our latitude, any body free to fall acquires in doing so (neglecting the resistance of the air) a velocity of 32⋅2 feet per second in each second during the interval between its release and arrest by the earth or any other body. This fact enables us to compare the force acting on a moving body when its weight in lbs. and its initial and final velocities in feet per second are known. An example will serve to make this clear.

Assume that a body weighs say 8 lbs. ; the pull of the earth or the attraction of gravity would generate a velocity, as we have seen, of 32⋅2 feet per second after it is allowed to fall, and at the end of the second time interval another 32⋅2 feet would be added, and so on. The force acting in this case is of course 8 lbs. These successive increases in velocity are termed the acceleration due to the force of gravity, is symbolised by the letter g.

Now, suppose the body to be at rest but free to move in any direction horizontally or vertically, and that a force is suddenly applied in such a way that the velocity of the body in its direction of motion is found, after a time interval of one second, to be 40 feet per second. Since the body was at rest at the beginning, and found to have the above velocity at