Does a cold ball bounce lower than a warm one?
- 🧍 Drop from standing: never climb
- 💧 Water
My hypothesis
If I change how warm the ball is, then how high the ball bounces will ______, because ______.
You fill in the blanks. Think about what happens to the rubber, and to the air inside the ball, when they get cold. A guess is a good because: the test finds out.
Change, measure, keep the same
CHANGE
how warm the ball is: Cold (from the fridge), Room, Warm (from warm water)
MEASURE
how high the ball bounces, in cm
KEEP THE SAME
- the same ball
- dropping it from the same 100 cm mark
- three drops in under a minute after the ball comes out
- the same floor
Scientists call the thing you change the independent variable and the thing you measure the dependent variable. The things you keep the same are the controls: if one of them changed too, you wouldn't know which change made the difference. Try each of the 3 levels 3 times.
What you need
- A tennis ball or a playground ball: 1
- Plastic bags: a zip bag that fits the ball
- A big bowl
- Warm water
- A thermometer (digital, or the red-liquid kind)
- A tape measure, or a long ruler
- Masking tape, to mark lines
- A stopwatch or a kitchen timer
Steps
- Tape the tape measure up a wall, with 0 at the floor, and mark 100 cm with masking tape.
- Read the thermometer in the room and write the temperature down.
- Hold the ball with its bottom at the mark and let go. Stand on the floor: never climb.
- A helper crouches by the tape and watches how high the ball's bottom gets on its first bounce.
- Write the height down, then drop the ball two more times, quickly.
- Seal the ball in a zip bag and leave it in the fridge, next to the thermometer, for 15 minutes.
- Read the thermometer, then take the ball out of its bag and drop it at once from the mark.
- Drop it twice more in under a minute, and write all three heights down.
- Run the tap until the water feels warm like a bath, never hot, and fill a bowl.
- Check the water with the thermometer and write the temperature down.
- Seal the ball in a zip bag and float it in the bowl for 15 minutes, turning it once.
- Take the ball out of its bag and drop it three times in under a minute, writing each height down.
- Find the mean for each temperature and draw a line graph.
Every step is one you can do yourself, with a grown-up nearby. Write each number down straight away, in the table below, so nothing is lost.
Your results table
Name ______________________ Fair day ____________
Question: Does a cold ball bounce lower than a warm one?
I changed: Ball temperature I measured: how high the ball bounces (cm)
| Ball temperature | Try 1 (cm) | Try 2 (cm) | Try 3 (cm) | Mean |
|---|---|---|---|---|
| Cold (from the fridge) | ||||
| Room | ||||
| Warm (from warm water) |
MY GRAPH (a line graph: ball temperature along the bottom, cm up the side)
What I noticed: ______________________________________________
From 4th grade, add the tries for each level and divide by how many there were: that's the mean, and it goes in the last column. Then draw a line graph, because the thing you change is a number that goes up.
Name ______________________ Fair day ____________
Question: Does a cold ball bounce lower than a warm one?
If I change how warm the ball is, then how high the ball bounces will ________________, because _____________________________________________
| I CHANGE | I MEASURE | I KEEP THE SAME |
|---|---|---|
| Ball temperature: Cold (from the fridge), Room, Warm (from warm water) | how high the ball bounces (cm) |
|
What I think will happen, in my own words:
Name ______________________ Fair day ____________
Question: Does a cold ball bounce lower than a warm one?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Does a cold ball bounce lower than a warm one?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Does a cold ball bounce lower than a warm one?
| Date | What I did | What I saw | What I think |
|---|---|---|---|
Name ______________________ Fair day ____________
Question: Does a cold ball bounce lower than a warm one?
My hypothesis was ☐ right ☐ partly right ☐ not right.
I know because my numbers show:
What surprised me, or what might have gone wrong (7th and up):
Next time I would test:
Idea: Change a second thing: test a second kind of ball at the same three temperatures, and graph each ball's bounce height divided by its drop height.
Why it works
A ball bounces because it squashes against the floor and then springs back. Cold rubber is stiffer and less springy, and the air inside a cold ball pushes back less, so more of the ball's energy is lost and it usually bounces lower. A warmer ball is usually bouncier.
Going further (7th and up): Change a second thing: test a second kind of ball at the same three temperatures, and graph each ball's bounce height divided by its drop height.
Board layout
- ❓ Question (10 × 8 in): Does a cold ball bounce lower than a warm one?
- 💭 Hypothesis (10 × 9 in): If I change how warm the ball is, then how high the ball bounces will ______, because ______.
- 🧺 Materials (10 × 12 in): 8 things: see your list.
- 🪜 Steps (22 × 9 in): 13 steps, three tries at each level.
- 📊 Results (22 × 16 in): Your table (Ball temperature down the side, tries across) and your line graph.
- ✅ Conclusion (10 × 14 in): My hypothesis was right / partly right / not right. I know because…
Materials to list: A tennis ball or a playground ball; Plastic bags; A big bowl; Warm water; A thermometer (digital, or the red-liquid kind); A tape measure, or a long ruler; Masking tape, to mark lines; A stopwatch or a kitchen timer.
Bring photos or drawings of your test. Nothing wet, hot, powered or alive on the table.
This project at your grade
| 4th–6th grade | Tries: three at each level. The table: units in the header and a mean column. The graph: a bar graph, or a line for a number that grows. The conclusion: right, partly or not, and the numbers that show it. |
|---|---|
| 7th grade and up | Tries: three or more at each level. The table: a mean for every level of both tests. The graph: a graph with two lines or two sets of bars. The conclusion: the numbers, what might have gone wrong, and a next question. Second variable: test a second kind of ball at the same three temperatures, and graph each ball's bounce height divided by its drop height. |
Every grade this project fits works out a mean. See every project for 4th grade, or print a blank results table.
What a judge will ask
- What did you change, and what did you measure? I changed how warm the ball is and measured how high the ball bounces, in cm.
- What did you keep the same, and why does that matter? I kept the same ball and dropping it from the same 100 cm mark the same, so the only difference was how warm the ball is.
- How many times did you test it? 3 times at each of my 3 levels.
- If you did it again, what would you change or test next? I'd test a second kind of ball at the same three temperatures, and graph each ball's bounce height divided by its drop height.
Make it yours
Keep this project on this device and Peabody counts down to your fair day, with a plan for each day. Nothing is sent anywhere.
Try next
👨👩👧 For grown-ups and teachers: how much to help, the safety rules, and running a school fair. Science fair v0.16.1 · Checked .