Bouncing Ball Example
Physics: AQA A Level, topic 4.1.9
Motion of a Bouncing Ball
To illustrate the concepts of motion in a straight line, let's consider a ball bouncing up and down. The ball starts at rest at 10 metres.
Displacement-time graph
- The ball starts (at time t = 0) at a height of 10 metres.
- The ball falls towards the ground.
- After the ball has hit the ground, it bounces back up.
- The same process repeats with the ball starting from a little lower each time.
Velocity-time graph
- To begin with (at t = 0), the ball is at rest (v = 0).
- The ball is then released and falls towards the ground.
- By convention, upwards is usually positive, so falling towards the ground means a negative velocity.
- The longer the ball falls, the quicker it gets.
- The ball hits the ground and instantaneously its velocity is reversed, it is now travelling upwards.
Velocity-time graph 2
- The further the ball travels upwards, the slower it gets - its velocity decreases but stays positive.
- When the velocity decreases to zero, the ball is at the top of its bounce, instantaneously at rest.
- The ball then falls and its velocity becomes increasingly negative.
- The cycle is repeated for every bounce.
Acceleration-time graph
- The acceleration of the ball is always the same: the acceleration due to gravity.
- The acceleration due to gravity is -9.81 m/s2.
- It is negative because it is pulling the ball downwards.
Test yourself on Bouncing Ball Example
If a ball is bouncing, what is the velocity of the ball at the very top of each bounce?
When an object is travelling upwards, what happens to the magnitude of its velocity?