Science 7–10 · Year 8

Bouncing ball: how much energy survives each bounce

Physical sciences — Change, content group Energy transfers (NSW Stage 4 focus area)

Practical, model not builtLow risk

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The idea

A dropped ball returns to a fixed fraction of its drop height on each bounce, and the missing fraction has been transformed into thermal energy and sound.

What you need

balls: tennis ball, golf ball, rubber bouncy ball, table-tennis ball, 1 each
metre rules taped to a wall to 2.0 m, 2
hard floor or a steel plate, 1
phone with slow-motion video, 1 (recommended for reading rebound heights)
electronic balance, 1

How to do it

Drop the tennis ball from 1.00 m (bottom of ball at the mark) onto the hard floor and read the height of the bottom of the ball at the top of the first bounce; use slow-motion video if the eye cannot follow. Five trials, average.
Repeat from 0.50 m, 0.75 m, 1.25 m and 1.50 m.
Plot rebound height against drop height and find the gradient; this is the fraction of energy kept in each bounce.
Repeat the 1.00 m drop for the other three balls and rank them.
Let the tennis ball bounce repeatedly from 1.00 m and record the height of the first five bounces; check that each is the same fraction of the one before.
Calculate the energy lost in the first bounce for the tennis ball from m g (drop height minus rebound height).

What you should see

Rebound height is proportional to drop height for each ball, so the graph is a straight line through the origin whose gradient is the fraction of energy kept. An approved tennis ball has to rebound to between 135 cm and 147 cm when dropped from 254 cm onto a rigid surface, which is a coefficient of restitution of 0.73 to 0.76 and a height fraction of 0.53 to 0.58, so from 1.00 m it rises to about 53 to 58 cm and to about 28 to 34 cm on the second bounce. The four balls keep different fractions, which gives the ranking. For a 58 g tennis ball dropped from 1.00 m that rebounds to 55 cm, the energy transformed in the first bounce is 0.058 kg x 9.8 N/kg x 0.45 m = 0.26 J, and across the approved rebound range it is 0.24 to 0.27 J.

What changes

What you change: drop height (m), or the type of ball
What you measure: rebound height (m)
What you keep the same: same surface
same ball for the height series
ball released from rest, not thrown

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

A ball can bounce higher than it was dropped from.
The lost energy disappears.
A heavier ball always bounces lower.

Safety card

Low riskLearners carry it out

Hazards

ball bouncing into faces or equipment

Controls

clear the drop zone
no hard balls above head height

Note

No hazardous chemicals or naked flames are used. Complete the school's risk assessment for the activity before the lesson; the NSW Department of Education Science safety and compliance page points to CSIS 1.7 (Risk assessment – a pre-requisite for risk control) for how to carry it out.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science 7–10 Syllabus (2023)SC4-CHG-01 SC4-WS-04 SC4-WS-05 SC4-WS-06
Australian Curriculum v9AC9S8U05AC9S8I02AC9S8I04AC9S8I05

Sources

The pages the author read to write this activity.

All Concept Studio activities