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Uniform and Non-uniform Motion

Class 7 Science · Chapter 8: Measurement of Time and Motion · NCERT Curiosity section 8.4

Learn

Neel watches a train on a straight track between two stations. It starts slowly, speeds up, runs steadily for a while, then slows and stops. Motion along a straight line is linear motion. While running at a constant speed, the train is in uniform linear motion; while speeding up or slowing down, it is in non-uniform linear motion.

Here are two trains, noted every 10 minutes. Train P: 0, 20, 40, 60, 80 km; it covers 20 km in every 10 minutes: uniform. Train Q: 0, 20, 35, 60, 80 km; it covers 20, 15, 25, 20 km: unequal distances in equal times, so non-uniform. Truly uniform motion over long distances is rare, which is why we use average speed.

Explore: uniform or non-uniform?

  1. Sort each motion.

Remember

  • Uniform linear motion: equal distances in equal times along a straight line.
  • Non-uniform motion: unequal distances in equal times; most real motion is non-uniform.

Quick check

A car covers 60 km in the first hour, 70 km in the second and 50 km in the third. Its average speed is …

  1. 60 km/h
  2. 70 km/h
  3. 180 km/h
  4. 50 km/h
Answer

60 km/h. Total 180 km ÷ 3 h = 60 km/h; the motion is non-uniform.

Think about it

Why is the motion of a car in city traffic non-uniform even on a straight road?

One answer

It keeps slowing down and speeding up for signals, crossings and other vehicles, so it covers unequal distances in equal times.

Practice

Practise with fresh questions at three levels (easy, medium, hard), some answered hands-on, with hints and worked answers. Get 4 of your last 5 right to finish the topic.