Energy activity — EP4: Bouncing balls

What are we learning in this activity?

Do an experiment
Write a lab report

In this practical you will be investigating the energy efficiency of a bouncing ball.

You will use this lab report template and this video of bouncing balls.

Background information

When a perfectly efficient ball is dropped:

Its gravitational potential energy is converted to kinetic energy as it falls.
All of its kinetic energy stays in the ball as it bounces.
The kinetic energy is converted back to gravitational potential energy as it rises.
It returns to the same height it was dropped from.

Real balls do not behave like this. Some energy is lost in the bounce, so they don’t bounce back as high as before. Eventually they stop bouncing.

The gravitational potential energy of an object can be calculated using this formula:

E = mgh

m is the mass of the object

g is the acceleration due to gravity, 9.8 m/s²

h is the height above the ground

When we calculate the efficiency of a ball bounce, the m and g terms cancel out and we are left with the formula

Efficiency = h (after) ÷ h (before) x 100%

The prac

In the video, different balls are dropped from 1 metre above the ground. There is a ruler to measure the height of the ball.

Your job is to:

Measure the height of the ball before and after each bounce
Calculate the energy efficiency of the bounce

Measure and calculate this for 3 bounces for each ball.

Note

This video was created with a fairly wide-angle lens. I dropped the balls from exactly 1m, but they appear to be above the ruler and bounce below the ruler. Don’t worry about this. Just:

Use a pencil to mark how far below the ruler the ball bounces. Then measure that distance against the ruler on the screen, and add it to all the heights.
Use a pencil to mark how far above the ruler the ball is. Then measure that distance against the ruler on the screen, and add it to the height before the first bounce.

Tech tip

You can step a YouTube video one frame at a time by pausing it. Then

press . (think >) to go forward
press , (think >) to go backward

Complete the lab report

Grading

I grade

Hand in a lab report.

E grade

Complete the “E grade” sections of the lab report.

D grade

Complete the “E grade” and “D grade” sections of the lab report.

C grade

Complete the “E grade”, “D grade” and “C grade” sections of the lab report.

B grade

Complete the “E grade”, “D grade”, “C grade” and “B grade” sections of the lab report.

A grade

Complete the “E grade”, “D grade”, “C grade”, “B grade” and “A grade” sections of the lab report.