|Background Bouncy balls like the one in the animation transfer mechanical energy when they bounce on a surface. To do so, the bouncy ball makes use of potential energy, kinetic energy, and its own elastic properties. As a bouncy ball is lifted, work is being done because a force is needed to elevate it (remember: W = Fd). As work is done a transfer of energy takes place. In the case of lifting a bouncy ball, the ball gains potential energy due to its height above the ground. As the ball falls, the potential energy it has is converted into kinetic energy (the energy of motion). When the ball strikes the ground, it bounces.|
As the ball bounces, some of its kinetic energy is transferred to the surroundings as evidenced by the ball not bouncing back to its original drop height. In this experiment you will test the relationship between the drop height of the bouncy ball and the amount of energy transferred to the surroundings. You will accomplish this by measuring the height of the ball after the first bounce and comparing the potential energy at the drop height to the potential energy at the first bounce.
|Note: The “Pre-Lab Discussion” video on the Project 3 page includes a demonstration of the experiment and data you may use in your lab report.|
SCIENTIFIC INVESTIGATION QUESTION
Construct a hypothesis that answers the following experimental question:
Does increasing the drop height of a bouncy ball affect the amount of energy transferred to surroundings after bouncing?
Note: When the ball doesn’t bounce up as high, energy has been transferred to its surroundings.
An experiment must contain a hypothesis. A hypothesis has two components:
- provides an explanation or an answer to a question that can be tested.
- includes a prediction that describes how the explanation or answer will be tested.
- is based on the experimental question.
- is best written in an “If…then…” format.
If you need to review how to form a hypothesis, view Enrichment: Forming a Hypothesis.
Recall that a controlled experiment (such as this one) involves independent and dependent variables. An independent variable is the variable that is purposely changed or manipulated. The dependent variable is the responding variable that is observed and measured because it changes in response to the independent variable. When the data is graphed, the independent variable is placed on the x -axis, and the dependent variable is placed on the y-axis.
Controlled experiments also involve controlled variables. These factors are kept the same throughout an experiment because they might cause a change in the dependent variable, but they are not being studied in the experiment.
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The materials presented below are recommended to complete this experiment. If you follow a different method to conduct this experiment, modify the materials list accordingly.
- 1 bouncy ball or golf ball
- a scale or balance
- a tape measure or meter stick
- tape (masking tape works best)
- marker or pen
- On a wall adjacent to the surface you will bounce the ball, measure 100 cm (1 meter) up from the surface and mark it with tape or pencil.
- Mark 10 cm, 20 cm, 30 cm, 40 cm, etc. all the way up to 100 cm. This will help you measure the bounce height accurately.
- If you don’t have a metric ruler, use an English ruler or tape measure and convert to centimeters using this Length Conversion Calculator
Follow the steps to complete the investigation. Use the lab handout to record the results of your investigation. You may need a lab partner to assist you with the procedure below:
- Use the scale to measure the mass of all of the bouncy ball. Record the mass in kilograms (kg) in Data Table 1 on the lab report. Convert English units (ounces, pounds) to kilograms using this Weight Conversion Calculator.
- Hold the ball at the 25cm mark and simply let go, do not throw the ball down.
- Allow the ball to bounce once and record the approximate height it reaches in Data Table 1 on the lab report. (This is “bounce height”, see image below.)
- Repeat steps 2 and 3 for a total of 3 trials for the first ball.
- Repeat steps 2 – 4 until you have collected data for the following drop heights
- 25 cm
- 50 cm
- 75 cm
- 100 cm
- 125 cm
- Calculate the average height of the bounce in centimeters.
- Calculate the height of the bounce in meters by dividing centimeters by 100.
| Results: Data Table 2: Calculations CALCULATING GRAVITATIONAL POTENTIAL ENERGY Calculate Gravitational PE (J) at Drop Height|
= mass (kg ) x acceleration/gravity (9.8 m/s2 x height (1 m)Calculate Gravitational PE (J) at Bounce Height
= mass (kg ) x acceleration/gravity (9.8 m/s2 x height (m)Calculate the difference between Gravitational PE (J) at Drop Height and Bounce Height.
= Gravitational PE (J) at Drop Height —
Gravitational PE (J) at Bounce Height
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