Measurement of Time and Motion

Overview

This chapter explains how we measure time and describe motion. We learn about different types of motion and how to calculate speed.

Key concepts

• Motion is a change in the position of an object with time.
• Types include linear, circular and oscillatory motion.
• Speed tells how fast an object moves.
• Time is measured with clocks; long ago people used sundials.
• A uniform motion covers equal distances in equal times.

Important terms / formulae

• Speed = distance / time.
• Unit of speed: metre per second (m/s) or km/h.
• Uniform motion: equal distance in equal time intervals.
• Oscillatory motion: to-and-fro motion, like a pendulum.

Solved example or key process

A car travels 120 km in 2 hours. Speed = distance / time = 120 / 2 = 60 km/h. So the car moves at sixty kilometres every hour. If it kept the same speed, in 3 hours it would cover 180 km.

Important questions

1. Write the formula for speed and its unit.
2. What is the difference between uniform and non-uniform motion?
3. Give one example of oscillatory motion.
4. A boy runs 100 m in 20 s. Find his speed.

Quick revision

Motion is change in position with time. Speed equals distance divided by time, measured in m/s or km/h. Motion can be uniform or non-uniform, and may be linear, circular or oscillatory.