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# Copy of How a tennis balls’ temperature affects its bounce height

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## Ricer Neil

on 13 October 2014

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#### Transcript of Copy of How a tennis balls’ temperature affects its bounce height

Hypothesis:
How high a ball bounces depends on the temperature of the ball.
Background research
Firstly we must consider what a squash ball is composed of, it is simply a rubber-like core filled with gas. When a squash ball is held above a surface it holds potential energy. As the ball falls through the air this potential energy changes to kinetic energy. Energy is neither gained nor lost, only transferred from one form to another. The gas molecules inside the ball are unorganised and move around very easily allowing the molecules to expand and contract. As a tennis ball hits the ground it is pushed inwards, in turn compressing the gas molecules inside. As it returns to its normal shape the gas molecules quickly expand again acting as a spring launching the ball back into the air. If the ball is elastic in nature, the ball will quickly return to its original form and spring up from the floor. This is Newton’s third law of motion which states that for every reaction, there is an equal opposite reaction; in this case when the ball pushes on the floor, the floor pushes back causing it to rebound.
Planning Log

Hypothesis - I hypothesize that a squash ball of a higher temperature will bounce higher than a ball of a lower temperature.

Outline - The experiment I will be conducting is the investigation of whether a change in a squash balls’ temperature affects the height at which it bounces. This allows me to easily collect quantitative data from the independent variable (temp) and the dependent variable (bounce height).

Experimental controls –
• Maintaining the same height from which all balls are dropped
•By using squash balls that are exactly the same
• Heating or cooling balls for an adequate period of time to ensure their exact temperature
• Using the same surface for all squash balls

Risk assessment – Heating the squash balls with boiling water could prove to be a possible hazard. To avoid any possible injuries care will be taken while pouring the hot water and tongs will be used to extract the squash ball from the hot water.
Validity and reliability – To ensure the reliability of the experiment the tests will be repeated to find an average. To ensure validity the experiment will aim to test the hypothesis proposed and all variables will be identified and controlled.

Aim – The aim of this experiment is to test whether the temperature of a tennis ball affects its bounce height.
Hypothesis - I hypothesize that a tennis ball of a higher temperature will bounce higher than a ball of a lower temperature.

FORMAL EXPERIMENTAL RECORD
Risk assessment – A potential and dangerous risk factor in this experiment involved heating one of the tennis balls in the oven. This risk was minimised by using a fairly low heat and by monitoring the tennis ball at all times so it didn’t melt and/or cause a fire.
Method
1.Four new tennis balls were removed from their container.
2.Tennis ball A was placed in a freezer (-15oC), tennis ball B was placed in a fridge (3oC) and tennis ball C was placed on a bench at room temperature (19oC). The tennis balls were left for 4 hours to adequately cool down.
3.Oven was preheated to 100oC.
4.Tennis ball D was placed in the preheated oven for 90 minutes.
5.Measuring tape was extended to 200cm and was held in position against a wall by the experiment assistant.
6.All four balls were individually dropped from the 200cm mark; this was repeated five times for each ball.
7.Bounce heights were recorded.

Variables
Independent variable – Temperature (oC)
Dependent variable – Bounce height (cm)
Controlled variables
•The height from which the balls were dropped from.
•The type and brand of the tennis balls.
•The period of time the balls were left to cool for (tennis ball D needed only 90 minutes to adequately heat up).
•The surface on which the balls bounced.

Validity – Validity was ensured in this experiment by identifying and controlling all variables that could alter the final result. The experiment also aimed to test the original hypothesis proposed allowing for more valid results.

Reliability – In this experiment, reliability was ensured by repeating the test on each ball for a total of five times. An average was then calculated from these results allowing for a more reliable final outcome.

Results
Conclusion
My original hypothesis indicated that a ball of a higher temperature will bounce higher than a ball of a lower temperature; the results obtained prove this correct. The pattern in the line graph above clearly shows that as the temperature of the ball increases, so does the bounce height.

Reflection
At first the tennis balls weren’t cooling down as much as I’d expected, but this was solved by leaving them to cool for an extended length of time. Another issue encountered involved being able to hold the tape measure on the wall and being able to record results accurately at the same time. This was overcome by getting another person to assist so I was free to accurately record results. There were very few problems encountered while conducting my experiment and all were easily overcome. If I were to conduct this experiment again I would use liquid nitrogen to cool one of the tennis balls to emphasize the effect temperature can really have on the bounce height.

Discussion
The experimental findings acquired from conducting this experiment could be extremely useful for a tennis player. Using these results, a tennis player could adjust his playing style to suit the climate he is playing in. In a warmer climate the ball will bounce higher than in a colder climate. A tennis player could win a match in a colder climate by preparing him/herself for lower bounce heights, giving them an advantage over an opponent oblivious to this.

Bibliography
•Why tennis balls bounce, viewed 16/08/2013, http://www.livestrong.com/article/344741-why-tennis-balls-bounce/

Ball B
Ball D
Ball being dropped from a height of 200cm
Tape measure positioned against wall
Fridge/Freezer Temperature
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