Q1.
I once watched a part of marathon on a straight road stretch. I noticed that some people seemed to be running at the same speed during that distance while some people would speed up or slow down. How were their motion different?
Answer
The two groups of runners were in two different kinds of linear motion.
| The runners who kept the same speed | The runners who sped up and slowed down |
|---|---|
| Uniform linear motion — moving along a straight line with a constant speed | Non-uniform linear motion — moving along a straight line with a speed that keeps changing |
| Cover equal distances in equal intervals of time (say 200 m in every minute) | Cover unequal distances in equal intervals of time (250 m in one minute, 150 m in the next) |
| Their speed at any moment equals their average speed | Their speed at a moment may be more or less than their average speed |
Both groups were running along the same straight road, so both motions are linear. What separates them is only whether the speed stays constant.
Why 'linear' and 'uniform' are two separate ideas: 'linear' describes the path — a straight line. 'Uniform' describes the speed — unchanging. A car going round a circular track at a steady 40 km/h has an unchanging speed but not a straight path, so it is not uniform linear motion.