tutor.eduforge
✦ Class 9 · Science
Motion
Imagine you need to get to a cricket match on time. You have two options: a bus or an auto. Which one will get you there faster, and how can we figure that o…
What this lesson covers
Step by step, in this order.
- 1Introduce the problem: getting to a cricket match on time, bus vs. auto. We need to measure their 'motion' to decide.
- 2Introduce Distance (how much ground was covered) and Displacement (the straight line from start to finish, with a direction). Example: the bus route is distance, a drone flying straight to the stadium is displacement.
- 3Confirm: Distance and displacement are equal only for motion in one straight line without turning back. Displacement can be zero (a lift going up and coming back to the same floor), but distance can never be zero for a moving object.
- 4TRY IT activity: Walk a rectangle in the playground. What's your total distance walked? What's your displacement?
- 5Introduce Speed (distance / time) and Velocity (displacement / time, with direction). Both have the SI unit m/s. Example: a scooter's metre shows speed, but a map app gives velocity to reach a destination.
- 6Worked numerical: A bus goes 60 km in 1.5 h, then 30 km in 30 min. Find its average speed. (Convert 30 min to 0.5 h. Total distance = 90 km. Total time = 2 h. Average speed = 45 km/h). Explain that for non-uniform motion, this is NOT the average of the individual speeds.
- 7Define Uniform motion (equal distances in equal intervals of time, like a train on a clear track) and Non-uniform motion (unequal distances in equal intervals, like an autorickshaw in traffic).
- 8Introduce Acceleration (change in velocity / time taken). Its SI unit is m/s². It's positive when speeding up, and negative (retardation) when slowing down. Example: a cricket ball speeds up after being thrown, then slows down as it rises.
- 9Worked numerical: A car goes from 18 km/h to 54 km/h in 5 s. Find its acceleration. (Convert speeds to m/s: 18 km/h = 5 m/s, 54 km/h = 15 m/s. a = (15-5)/5 = 2 m/s²).
- 10Introduce Distance-time graph: a straight line means uniform speed (its slope IS the speed). A horizontal line means the object is at rest. A curve means the speed is changing. Activity: plot distance against time from a friend walking at a steady pace.
How it looks
A real board, not a video.
This board is from a different Science lesson — yours will look like this. She writes and draws while she explains, and stops to check you followed.
Doubts this lesson clears up
- Why is displacement important if distance tells me how far I've gone?
- Can something have speed but zero velocity?
- How can something be accelerating if its speed isn't changing?
- Why do we need three equations for motion? Can't one do it?
- What's the difference between retardation and negative acceleration?
- Does gravity always make things accelerate at 9.8 m/s²?
Class 9 Science
More lessons like this
Give your child a better way to learn Maths & Science.
Interactive. NCERT-aligned. Any time, anywhere.