Bouncing ball energy lab
01 // Question
How do the tested ball samples differ in mean first-rebound height?
A testable question names one thing you change (ball type) and one thing you measure (bounce height).
02 // Variables
Independent
Type of ball- Tennis ball
- Basketball
- Ping pong ball
- Rubber bouncy ball
Dependent
First-rebound height- Three heights in cm per ball
- Mean height and range
- Mean height as a percent of the 100 cm drop
03 // Hypothesis
IF different ball samples are dropped from the same fixed height, THEN their mean first-rebound heights will differ, BECAUSE their construction and interaction with the floor can change how motion energy transfers during impact.
04 // Procedure
1. Set a safe, fixed height
Mark 100 cm above the floor at the ball's lower edge, at a height students can reach while standing. Put the vertical scale beside the path in the same plane as the motion.
2. Release each ball from rest
Align the ball's lower edge with the 100 cm mark and open your fingers without pushing, spinning, or throwing it. Use the same dry, level hard floor.
3. Read the first-rebound peak
From a side view perpendicular to the scale, record the ball's lower edge at its first-rebound peak, using that same edge as the release-height reference. Slow-motion video can help.
4. Keep three raw trials
Record three first-bounce heights in centimeters for each ball, reading the same lower edge each time. Repeat a sideways or unclear drop and note why it was repeated.
5. Summarize without overclaiming
Find mean height and range (highest minus lowest). Calculate mean height ÷ 100 cm × 100%; this is a height fraction, not percent of kinetic energy.
Materials // Prepare the bench
- Several ball types
- meter stick or tape measure
- masking tape
- hard level floor
- phone camera or stopwatch
- clear drop zone
05 // Data table
| Ball type | Trial 1 (cm) | Trial 2 (cm) | Trial 3 (cm) | Mean height (cm) |
|---|---|---|---|---|
| Tennis ball | ____ | ____ | ____ | ____ |
| Basketball | ____ | ____ | ____ | ____ |
| Ping pong ball | ____ | ____ | ____ | ____ |
| Rubber bouncy ball | ____ | ____ | ____ | ____ |
Illustrative summary for a 100 cm drop (not target results)
| Ball sample | Mean rebound (cm) | Range (cm) | Mean height as % of drop |
|---|---|---|---|
| Tennis ball | 55.3 | 3 | 55.3% |
| Basketball | 60.0 | 2 | 60.0% |
| Ping-pong ball | 70.0 | 4 | 70.0% |
| Rubber bouncy ball | 86.7 | 3 | 86.7% |
Formula Mean height returned (%) = (mean of 3 first-rebound heights ÷ 100 cm drop height) × 100
06 // What to expect
The ranking depends on the exact ball, its pressure and condition, the floor, and the measurement. Do not treat a rubber ball or any other category as guaranteed to rebound highest; compare the samples you actually tested.
A rebound-height ratio is not the fraction of kinetic energy returned. Impact transfers energy to sound, warming, deformation of the ball and floor, and other motion. This activity uses height as a simple comparison, not a direct energy measurement.
The illustrative table shows one possible set of readings only. Three drops of one ball are repeated measurements of that sample, not three different balls; results do not establish a ranking for every ball of that type.
07 // Lab notes
- Use a release height that students can reach while standing on the floor. Do not climb on a chair or stool to set the drop.
- Keep the same dry, level hard floor, camera angle and first-peak rule. A vertical scale placed in a different plane from the ball can create a parallax error.
- Read the first rebound only. Later peaks follow extra impacts and cannot be compared as if they were the first bounce.
- Optional separate investigation: use one ball and compare first-rebound heights from several reachable release heights. Keep the ball, floor and release method fixed, repeat each height, and graph mean rebound height against drop height; do not mix these readings into the ball-type comparison.
08 // Remember
A lower rebound shows that energy transferred during impact. Energy changes form; the height ratio is not an energy percentage.
09 // Measure a bounce from a defined height
Mark a release height and a vertical scale on the wall behind the landing zone. Hold the ball at the same point each time and release without pushing or spinning it. Record the first rebound height, or use video to review the peak frame. If several ball types are compared, use balls with similar size when possible and test them on the same floor surface.
The ball type is the independent variable; rebound height, contact time, or number of bounces may be the response. Keep release height, surface, temperature, and measurement method constant. Repeat each ball several times. A soft carpet and a hard tile surface produce very different results, so record the test surface rather than attributing every change to the ball.
10 // Relate rebound to energy transfer
A falling ball's gravitational potential energy becomes motion energy, then the ball and floor deform at impact. Some energy is returned to the ball for the rebound; some transfers to sound, heat, and permanent or temporary deformation. Rebound height is a useful comparison measure, but it is not a direct measurement of one single energy-loss pathway. The material, internal pressure, temperature, and surface all affect the result.
Calculate the rebound ratio by dividing rebound height by release height. A ratio closer to one indicates a higher rebound under that trial's conditions, but it does not mean the ball is perfectly elastic. Plot rebound height or ratio for each ball type and show individual trials. If the pattern is inconsistent, check the release point, camera angle, scale alignment, and whether the ball struck the same part of the floor.
11 // Use slow-motion video and keep the drop zone clear
Slow-motion video can help identify the ball's highest point, but place the camera perpendicular to the scale to limit parallax. Keep the phone outside the impact area and secure it on a stand. Students should stand back while balls are dropped and should retrieve them only after the test is complete. Do not drop heavy or hard objects from heights above the approved classroom limit.
An extension can compare the same ball on two surfaces or compare temperature effects for a ball with measurable internal pressure, but not both at once. Repeat trials and explain why the result applies to the tested ball and surface. Use a consistent way to define the rebound peak, because a small difference in frame selection can change the measured height.
12 // Compare rebound consistently and explain energy transfer
A ball’s rebound height is usually lower than its release height because some mechanical energy is transferred to sound, heat, deformation, and motion of the floor and air. The fraction of height returned can be used as a simple comparison, but it is not a full measurement of energy unless the setup and assumptions are stated. Different balls also have different shapes, internal pressures, and surface materials, so identify the exact samples tested.
Release each ball without pushing it from a marked height over the same hard surface. Film from the side with a scale in the same plane as the ball, then read the ball's lower edge at the first-bounce peak, using that same edge as the release-height reference. Repeat trials and report the range. Avoid catching or pressing a bouncing ball near someone’s face, and do not compare results from different floors as if only ball type changed.
13 // Questions people ask
Does a rubber ball always bounce higher than a tennis ball?
No. The outcome depends on the exact ball and its pressure or condition, along with the floor and measurement method. Test and report the samples used instead of assuming a universal ranking.
Does a 60% rebound-height ratio mean 60% of the ball's kinetic energy returned?
No. It means the mean rebound height was 60% of the release height. Kinetic energy depends on mass and speed, so height ratio alone is not an energy percentage.
Why use the same part of the ball for release and rebound measurements?
Reading the lower edge at release and at the first-rebound peak keeps the reference point consistent. A side view perpendicular to the scale and a scale in the same plane reduce parallax.
What should I report besides the mean?
Keep all three raw heights and report their range (highest minus lowest) as well as the mean. The range shows how spread out those three readings were.
14 // Keep going
Can you explain the investigation?
Bouncing ball energy lab · Student Data Sheet
Question: How do the tested ball samples differ in mean first-rebound height?
Hypothesis: If different ball samples are dropped from the same fixed height, then their mean first-rebound heights will differ, because their construction and interaction with the floor can change how motion energy transfers during impact.
Materials
- Several ball types
- meter stick or tape measure
- masking tape
- hard level floor
- phone camera or stopwatch
- clear drop zone
Safety before starting
- Use small, intact balls on a clear, level floor and a release height reachable while standing. Keep faces, feet, pets and breakable objects away; drop, do not throw. Retrieve only after balls stop.
- Wipe up any water or debris before testing so nobody slips while retrieving a ball.
Lab notes
- Use a release height that students can reach while standing on the floor. Do not climb on a chair or stool to set the drop.
- Keep the same dry, level hard floor, camera angle and first-peak rule. A vertical scale placed in a different plane from the ball can create a parallax error.
- Read the first rebound only. Later peaks follow extra impacts and cannot be compared as if they were the first bounce.
- Optional separate investigation: use one ball and compare first-rebound heights from several reachable release heights. Keep the ball, floor and release method fixed, repeat each height, and graph mean rebound height against drop height; do not mix these readings into the ball-type comparison.
Variables
Independent: Type of ball · Dependent: First-rebound height
Keep constant: same 100 cm release height · same hard, flat floor · release from rest, not a throw · same peak-reading rule and camera/scale position
Procedure
- Set a safe, fixed height: Mark 100 cm above the floor at the ball's lower edge, at a height students can reach while standing. Put the vertical scale beside the path in the same plane as the motion.
- Release each ball from rest: Align the ball's lower edge with the 100 cm mark and open your fingers without pushing, spinning, or throwing it. Use the same dry, level hard floor.
- Read the first-rebound peak: From a side view perpendicular to the scale, record the ball's lower edge at its first-rebound peak, using that same edge as the release-height reference. Slow-motion video can help.
- Keep three raw trials: Record three first-bounce heights in centimeters for each ball, reading the same lower edge each time. Repeat a sideways or unclear drop and note why it was repeated.
- Summarize without overclaiming: Find mean height and range (highest minus lowest). Calculate mean height ÷ 100 cm × 100%; this is a height fraction, not percent of kinetic energy.
Record your observations
| Ball type | Trial 1 (cm) | Trial 2 (cm) | Trial 3 (cm) | Mean height (cm) |
|---|---|---|---|---|
Illustrative summary for a 100 cm drop (not target results)
| Ball sample | Mean rebound (cm) | Range (cm) | Mean height as % of drop |
|---|---|---|---|
Formula: Mean height returned (%) = (mean of 3 first-rebound heights ÷ 100 cm drop height) × 100
Answer key and expected pattern
The ranking depends on the exact ball, its pressure and condition, the floor, and the measurement. Do not treat a rubber ball or any other category as guaranteed to rebound highest; compare the samples you actually tested.
A rebound-height ratio is not the fraction of kinetic energy returned. Impact transfers energy to sound, warming, deformation of the ball and floor, and other motion. This activity uses height as a simple comparison, not a direct energy measurement.
The illustrative table shows one possible set of readings only. Three drops of one ball are repeated measurements of that sample, not three different balls; results do not establish a ranking for every ball of that type.
Remember: A lower rebound shows that energy transferred during impact. Energy changes form; the height ratio is not an energy percentage.