Investigating Science 11–12 · Year 11

Energy transfer in a bounce: tennis ball rebound against the ITF standard

Module 4: Theories and Laws

Practical, model not builtLow risk

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The idea

Energy is conserved but not kept as motion: a bouncing ball returns only part of its gravitational energy, and a regulation tennis ball must lose between about 42 and 47 per cent of it in each bounce.

What you need

three tennis balls (new and worn), balance to 0.1 g
metre rules taped to a wall up to 2.6 m, a concrete floor or heavy smooth paving slab
phone with slow-motion video, a stable step
a carpet square and a grass patch for comparison

How to do it

Hold each ball with its bottom at 254 cm above the concrete and release it from rest; film the bounce.
Read the rebound height to the bottom of the ball from the video; repeat five times per ball.
Calculate the fraction of energy retained, h_rebound/h_drop, and the coefficient of restitution e = √(h_rebound/h_drop).
Compare each ball with the ITF standard.
Repeat on carpet and grass.
Account for the energy that is not returned as motion.

What you should see

ITF Rules of Tennis Appendix I requires Type 2 (medium) balls to rebound 135 to 147 cm, and the ITF rebound test (technical booklet, method TB 04/01) drops the ball from 254 cm, measured to the bottom of the ball, onto a smooth, rigid block, so a conforming ball keeps 53.1 to 57.9 % of its gravitational energy and has e = 0.729 to 0.761. For a 57.7 g ball (mass range 56.0 to 59.4 g) the 1.44 J at release falls to 0.76 to 0.83 J at the top of the rebound, so 0.61 to 0.67 J per bounce is transferred to internal energy and sound. Worn balls rebound lower, and carpet and grass return less still.

What changes

What you change: ball (new or worn) and surface
What you measure: rebound height
What you keep the same: drop height 254 cm to the bottom of the ball
release from rest
same temperature
five drops per ball

Common misconceptions

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

Energy is lost, meaning it disappears.
A good ball bounces back to the height it was dropped from.
The bounce depends only on the ball, not the surface.

Safety card

Low riskLearners carry it out

Hazards

working at height on a step

Controls

use a stable step with a spotter

Note

No hazardous chemicals or heat sources: record the activity in the school's RiskAssess risk assessment, following the NSW Department of Education Science safety and compliance page; the Chemical Safety in Schools package is not triggered.

Curriculum references

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

Investigating Science Stage 6 Syllabus (2017), NESA; currentINS11-11 INS11/12-5 INS11/12-6 INS11/12-7
Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

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