Excellence Exemplar for a Fair Test
AS90727 (version 2) Science 3.1 Carry out a practical scientific investigation
with guidance
How Temperature affects the Bounce of Tennis Balls
Initial trialling:
INITIAL IDEA: Mr
told us about the extended investigation today. I
am a keen tennis player and I think that the temperature of the day may affect the
bounce of the balls I am using. So I think that I will design an experiment around that
idea.
PURPOSE: To determine if temperature affects the distance that a tennis ball
bounces.
HYPOTHESIS: If temperature is increased and all other factors remain the same,
then the ball will bounce further. I expect this because in cold conditions air contracts
and the ball will act as if it is slightly deflated.
INDEPENDENT VARIABLE:
The temperature will be measured in degrees centigrade, using a thermometer. My
range of temperatures is going to be from 6oC (see notes later)to 26oC. I will vary the
temperature by using heaters, and by the time of day that I do an experiment.
DEPENDENT VARIABLE:
The distance between the balls first and second bounce. To be measured with a tape
measure in cm.
JUSTIFICATION FOR METHOD:
I wanted to use tennis balls also because other hollow balls such as netballs loose
air more quickly than tennis balls, which would have introduced an unnecessary
error.
I trialled two ways of determining the dependent variable. Firstly I dropped the balls
from the same height and measured how high the ball bounced. Because I was
working on my own I didn’t think that I could judge the height of the bounce very
accurately. Then I decided to do the method mentioned next. I designed a ramp so
that I could accurately set the ball off from the same height each time. I thought
about how to accurately determine where the ball bounced and I used talcum powder
on the concrete floor as you could then very accurately record where the ball landed.
The ball made a crater when it bounced with a peak in the middle. This meant that I
was able to measure from the peak of the first bounce to the peak of the second
bounce. I trialled this visually at 7oC and at 20oC and found that I was getting a
significant difference between the two temperatures.
Method trialled and the reasons for the
design explained and justified.
EQUIPMENT:
 Ramp with recorded height, length and angle (the actual dimensions do not
matter just record them). Like in picture 3
 Tape measure (or long ruler of any kind)
 Thermometer
 Talcum powder
 Tennis balls x3
 Heaters
 Aluminium garage – I chose this because I could keep the garage at a constant
temperature as I did the experiment.
INITIAL METHOD:
1. Set up your ramp so it is above a smooth and level surface.
2. Sprinkle the floor with talcum powder so the coating is light.
3. Record the temperature.
4. Sweep with a broom or brush so the talcum powder is in lines.
5. Hold the tennis ball at the top of the ramp let it roll down the ramp (do not push it,
a block of wood would be a good thing to start it with).
6. Watch it bounce to get a general idea of where it landed on its first and second
bounce. Then look at the talcum powder. Look for craters and measure the
distance from the peak in the crater caused by the first bounce and the one
caused by the second bounce.
7. Record your results.
8. Repeat steps 2-7 5 times using the same tennis ball.
9. Repeat steps 2-8 using a different tennis ball.
10. Repeat steps 2-9 with 5 different temperatures. Note you don’t need a specific
temperature just to measure it precisely.
11. Process the data to determine the kinetic energy lost.
Initial method written up as
part of the trialling.
Final Report: How Temperature affects the Bounce of
Tennis Balls
BACKGROUND:
I am a keen tennis player and I practise at all times of the day. I started noticing that
the balls I used sometimes seemed to bounce higher in the middle of the day than
when I practised early in the morning. I began to wonder if temperature affected the
bounce of tennis balls. I decided to make this the topic of my extended practical
investigation.
I decided to use one brand of balls and test them over a range of temperatures. This
made my investigation a fair test.
PURPOSE: To determine if temperature affects the distance a ball will bounce.
Statement of purpose
HYPOTHESIS: If temperature is increased and all other factors remain the same,
then tennis balls will bounce further.
SCIENCE IDEAS:
I expect this because in cold conditions air contracts and the ball will act as if it is
slightly deflated. The density, pressure and temperature of a gas are related. When a
gas moves against an object, such as the wall of a tennis ball, it pushes on the
surface of the object - pressure. Gases can be expanded or compressed; they can
expand to fill a new larger volume. The mass doesn't change, but the volume
increases, so the density of the gas decreases in the new volume.
The structure of a tennis ball has a fabric covering and a hollow inner core of a
rubber-like substance. Inside the core is a gas which fills the entire inner core of the
ball. A tennis ball bounces because the tennis ball and the gas inside act like a
spring. As the tennis ball strikes the court the bottom of the ball is pushed in. The
tennis ball material is pliable and deforms (bends). The compressed (pressed in) ball
has less volume than the original uncompressed ball. As the ball comes off the court
the gas and tennis ball material act like a spring and the ball returns to its original
shape. As the temperature increases the molecules of the gas expand and move
around more inside the ball. As the molecules move more they strike the inner
surface of the ball and apply more pressure to it. Balls with more air pressure in them
bounce better because air, when compressed, will uncompress (spring back) with
little or no energy loss. A ball that has higher air pressure in it will not squash as
much during the collision, and so less energy will be lost. Therefore the ball will
bounce further.
Explanation of relevant science ideas –could be
written up at the beginning of the report or the end as
part of the discussion.
INDEPENDENT VARIABLE:
Temperature to be measured in degrees centigrade using a thermometer. My range
of temperatures is to be 6oC, 11 oC, 16 oC , 21 oC and 26oC.
Independent variable with valid range
DEPENDENT VARIABLE:
Distance between the balls first and second bounce, taken from the peak in the
centre of the crater in the talcum powder. To be measured with a tape measure in
centimetres.
Accurate measurement of dependent variable
EQUIPMENT:
 Ramp with recorded height, length and angle
 Tape measure (or long ruler of any kind)
 Thermometer
 Talcum powder
 3 tennis balls of the same brand
 Heaters
 Suitable cleared space (I used an aluminium garage with a concrete floor)
FINAL METHOD:
1. I set up my ramp as in picture 1 so it is above the garage floor, which was a
smooth and level concrete surface.
2. I sprinkled the floor with talcum powder so the coating was light and swept it so
that there were faint lines across it.
3. I swept the floor with a brush so the talcum powder was in line.
4. I recorded the temperature.
5. I then held the tennis ball at the top of the ramp (62.4 cm) and let it roll down the
ramp (I didn’t push it but used a block of wood to start it with).
6. I watched it bounce to get a general idea of where it landed on its first and
second bounce. Then I looked at the talcum powder. It showed peaks in the
craters (in the talcum powder) and so I measured the distance from the peak in
the crater caused by the first bounce and the one caused by the second bounce.
7. I recorded my results.
8. I swept the talcum powder after each bounce.
9. I repeated steps 2-7 5 times using the same tennis ball.
10. I repeated steps 2-8 using a different tennis ball.
11. I repeated steps 2-9 with 5 different temperatures. They were 7oC, 11 oC, 16 oC,
21 oC, and 26 oC. I was not able to get the room to 6oC, so I measured 7oC
instead.
12. I varied the temperature by using heaters for heat up the space and by getting up
early in the morning to do the low temperatures.
13. The fixed variables are listed below.
14. I processed the results by
 averaging the results for each ball and then for all 3 balls.
 graphing temperature against distance travelled.
A method describing the independent variable with a valid range, the accurate
measurement of the dependent variable and the control of most other variables.
Picture 1: Ramp for ball
Fixed variables (Potential Errors)
Temperature fluctuation during an
experiment
Barometric pressure
Tennis ball wearing out
Talcum powder on ball
Brand of talcum powder
Brand and age of tennis ball
Tennis ball
Mark on tennis ball
Even start
Talcum powder consistency
How to minimize effect of these
Not much of a problem, but at very low
temperatures your body heat can rise the
temperature in a small room. So if you
observe the temperature rising leave the
room for a short time to let it cool down.
This is a tricky one but on a clear day
(without a storm approaching) it will not
change substantially so do all tests on a
clear day within 24 hours of each other.
Use good tennis balls of same brand and
do the colder temperatures first.
Wipe the ball clean after each trial with a
dry towel.
Use same brand.
Use same brand of new balls.
Mark each tennis ball and get individual
results for each one.
Do the mark as small as possible and in
biro, not anything that is likely to change
the flight path of the ball.
Start each ball with the same object eg
block of wood at same height (62.4 cm)
Use the same brush and try to keep the
talcum powder to as thin and as even as
possible.
A table showing:
- how most other variables were controlled
- discussion of sources of error
RESULTS:
The results were averaged. A graph was drawn showing the averaged data which
highlighted the aberrant data for one ball at 26oC. This was removed and the
averaged data graphed
Table showing Results: temperature (oC) vs distance (cm) between 1st and 2nd
bounce.
weight (g)
ball 1
58
temperature Ball 1
.
ball 2
55.9
ball 3
56.8
Ball 2
Ball 3
7
7
7
7
7
147
142
149.5
152
145
140.5
141
140
144.5
136.5
147.5
144
150
141.5
154
11
11
11
11
11
150
144.5
152
153.5
146
143
142
137.5
147
145.5
147
149.5
145.5
145.5
150
16
16
16
16
16
149
151
154
150.5
150
145
144
143
147
145
147
152
146.5
146.5
144.5
21
21
21
21
21
151.5
153
156
148
149.5
148
150
151.5
147.5
145.5
148
151
146
147.5
153
26
26
26
26
26
139
136
146
135
146
149
152
145
150
152
150
145.5
153.5
149.5
150
Average Average Average Average
Ball 1
Ball 2
Ball 3
all balls
150.6
140.5
148.8
146.6
152.6
146.3
149.4
149.4
152.9
146.1
149.8
149.6
154.4
150.6
151.6
152.2
145.2
152.2
152.4
152.3
Sufficient, reliable data consistent with the final
method, recorded systematically with appropriate
precision. Appropriate treatment of extremes of data
Graph 1:
Disrance (cm)
Average distance balls bounced at different
temperatures
156
154
152
150
148
146
144
142
140
138
Average Ball 1
Average Ball 2
Average Ball 3
0
10
20
30
temperature in degrees Centigrade
Graph 2:
Average distance balls bounced at different
temperatures with aberant data removed
160
Average Ball 1
Average Ball 2
Average Ball 3
Linear (Average Ball 2)
Linear (Average Ball 3)
Linear (Average Ball 1)
155
150
145
140
135
0
5
10
15
20
25
temperature in degrees Centigrade
Graph 3:
30
Average distance of bounce for all balls vs
Temperature
154
Distance (cm)
153
152
Average
of all
balls
151
150
Linear
(Averag
e of all
balls)
149
148
147
146
0
5
10
15
20
25
30
Temperature in degrees Centigrade
Processing of data using graphs and/or other
techniques
INTERPRETATION:
There was a definite relationship between temperature and the distance that the ball
bounced, in that the higher the temperature the greater distance the ball bounced.
This relationship was true for all the balls that were used, except for one ball at 26oC.
I decided to eliminate this aberrant data.
Interpretation identifies trend in processed data
CONCLUSION:
My hypothesis stated that if temperature is increased and all other factors remain the
same, then tennis balls would bounce further. My processed data shows that this is
true for the 3 tennis balls that I tried. The increase in temperature expands the gases
inside the tennis ball, which move around more inside the ball. As the molecules
move more they strike the inner surface of the ball and apply more pressure to it.
Balls with more air pressure in them bounce better because air, when compressed,
will uncompress (spring back) with little or no energy loss. A ball that has higher air
pressure in it will not squash as much during the collision, and so less energy will be
lost. Therefore the ball will bounce further which is what my investigation showed.
Valid conclusion related to the purpose of the investigation.
Further explanation of the relevant science ideas
DISCUSSION:
I was satisfied that I had controlled as many fixed variables as I could. Doing the
experiment in an aluminium garage meant that I was satisfied that I kept the
temperature constant for each test. However, there are certainly some things that I
could do to improve my experiment.
 Reliability.
The data is very reliable because I controlled as many variables as I could. I used
tennis balls because they would not lose air as fast as other hollow balls.
 Validity.
This was a valid method although it differed from the methods that I had researched.
I used this method as I felt that I could get more accurate results seeing that I was
doing this investigation on my own.
 Limitations.
There were limitations to this investigation.
- At very low temperatures your body heat can raise the temperature in a small
room. So if the temperature rose I would leave the room for a short time to let it
cool down.
- A sudden decrease or increase in barometric pressure would change the
pressure in a ball. I did this experiment on the same day when the weather was
not changing.
- Measuring the length bounce meant that I did not take into account the height of
the bounce. I decided that this was still a valid experiment and that it was not
necessary to measure the bounce.
 Future Investigations.
- I would be interested to try the same experiment using different types of hollow
balls to see if this trend was true for other hollow balls
- I could have tried more of the same brand of tennis ball to see if the aberrant
data at 26oC for one ball was true for other balls at that temperature or genuine
aberrant data.
- I would like to try the method of just dropping the ball from a certain height and
measuring the height of the bounce. It would be interesting to compare the 2 sets
of data and validate my method that way.
- I did consider working out the kinetic energy lost but I decided that these results
showed a sufficient trend and proved the hypothesis.
Discussion of reliability of data, discussion of sources of error,
ideas for future investigations. Justification for final method found
in the trialling.
BIBLIOGRAPHY:
http://wings.avkids.com/Curriculums/Tennis/hotcold_summary.html
http://www.phys.virginia.edu/Education/outreach/8thgradesol/Effectoftemperature.ht
m
http://www.picotech.com/experiments/squash_ball/