V2

V1

y2

y(t) y1

FIGURE 16.1 Position-time function for an object moving on a straight path.

16.2 Measurement of Linear Velocity

The problem of velocity measurement is somewhat different from that of measurement of other quantities in that there is not a large number of transducer types and transducer manufacturers from which to choose for a given problem. Frequently, the problem is such that the person must use his/her knowledge of measurement of other quantities and ingenuity to develop a velocity measurement method suitable for the problem at hand. Velocity is often obtained by differentiation of displacement or integration of acceleration. As background information for this, the necessary equations are given below.

Figure 16.1 shows a graph that represents the position of an object as a function of time as it moves along a straight, vertical path (y direction). The quantity to be measured could be an average velocity, and its magnitude would then be defined as follows:

for the time interval t1 to t2. As the time interval becomes small, the average speed becomes the instantaneous speed Vy, and the definition becomes:

© 1999 by CRC Press LLC