A simple pendulum is the simplest device that can be used to measure time based on periodic motion. It is an arrangement of a heavy mass suspended from a string which completes one to and fro motion in exactly the same time. The heavy mass is called bob of the pendulum.

Time period is a term which is used for a periodic motion. It is the interval of time after which the motion is repeated. For example, the oscillatory motion of a simple pendulum is periodic. Hence, the time taken by it in completing one oscillation is called its time period.

The distance travelled by a body in unit time is called speed. The SI unit of speed is metre per second ( m / s ). Speedometer is used to show the speed of the vehicle. It shows the speed of the vehicle in km h .