While discussing the Fundamental quantities, we talked about Time with Second as its S.I. Unit. Now how can we measure time? This is a simple question but it get’s trickier as you climb in your understanding of Physics.

Of course you know you can use your watch or clock to measure time. You can also use your pulse rate or heart beat to count or measure time. But have you heard of a Pendulum?

How to measure time with a Simple Pendulum:

Pendulums are in common usage. Some have crucial uses, such as in clocks; some are for fun, such as a child’s swing; and some are just there, such as the sinker on a fishing line. For small displacements, a pendulum is a simple harmonic oscillator. A simple pendulum is defined to have an object that has a small mass, also known as the pendulum bob, which is suspended from a light wire or string, such as shown in Figure 16.14. Exploring the simple pendulum a bit further, we can discover the conditions under which it performs simple harmonic motion, and we can derive an interesting expression for its period.

We begin by defining the displacement to be the arc length s . We see from Figure 16.14 that the net force on the bob is tangent to the arc and equals −mg sin θ . (The weight mg has components mg cos θ along the string and mg sin θ tangent to the arc.) Tension in the string exactly cancels the component mg cos θ parallel to the string. This leaves a net restoring force back toward the equilibrium position at θ = 0 .

Watch the video below to learn how you can measure time with a simple pendulum