of the body will be represented in magnitude and in direction by the arrow R. That is to say, after the large turning force has acted for a short time the body will be found spinning about R as an axis, and the number of revolutions per second will be represented by the length of R. The geometrical relationship between the arrows S', S", and R is completely represented in the triangle OMN of Fig. 2, which triangle is shown by itself in Fig. 3.
A turning force is usually called a torque, thus the turning or
|Fig. 2.||Fig. 3.|
twisting force which is exerted upon a screw driver is a torque. A torque may be completely represented by an arrow drawn parallel to the axis of the torque, pointing in the direction in which a right-handed screw would travel if turned by the torque, and having a length which represents the magnitude or value Fl of the torque to scale. Thus the arrow T in Fig. 4 represents the torque due to the two forces FF.
The effect of an unbalanced torque upon a body is to produce a spin-velocity about the same axis as the torque, the amount produced
- This proposition is entirely correct if by spin we understand that spin momentum is meant; the spin-velocity of a body is sometimes greatly complicated by its lack of symmetry, and these complications are ignored in the present discussion.