The unit of ν is thus s – . After the discoverer of radio waves, Heinrich Rudolph Hertz ( – ), a special name has been given to the unit of frequency. It is called hertz (abbreviated as Hz). Thus, hertz = Hz = oscillation per second = s – ( .
) Note, that the frequency, ν , is not necessarily an integer. u Example . On an average, a human heart is found to beat times in a minute. Calculate its frequency and period.
Answer The beat frequency of heart = /( min) = /( s) = . s – = . Hz The time period T = /( . s – ) = .
s ⊳ . . Displacement In section . , we defined displacement of a particle as the change in its position vector.
In this chapter, we use the term displacement in a more general sense. It refers to change with time of any physical property under consideration. For example, in case of rectilinear motion of a steel ball on a surface, the distance from the starting point as a function of time is its position displacement. The choice of origin is a matter of convenience.
Consider a block attached to a spring, the other end of the spring is fixed to a rigid wall [see Fig. . (a)]. Generally, it is convenient to measure displacement of the body from its equilibrium position.
For an oscillating simple pendulum, the angle from the vertical as a function of time may be regarded as a displacement variable [see Fig. . (b)]. The term displacement is not always to be referred Fig.
. (a) A block attached to a spring, the other end of which is fixed to a rigid wall. The block moves on a frictionless surface. The motion of the block can be described in terms of its distance or displacement x from the equilibrium position.
Fig. . (b) An oscillating simple pendulum; its motion can be described in terms of angular displacement θ from the vertical. in the context of position only.
There can be many other kinds of displacement variables. The voltage across a