# Bouncing Basketballs: How Much Energy Does Dribbling Take?

 Difficulty Time Required Very Short (≤ 1 day) Prerequisites None Material Availability Readily available. See the Materials and Equipment list for details. Cost Very Low (under \$20) Safety No issues

## Abstract

Playing basketball can be hard work. Players not only constantly run around the court, but just dribbling the basketball takes a lot of effort, too. Why is that? It has to do with how the basketball bounces. When the ball hits the court, its bounce actually loses momentum by transferring some of its energy into a different form. This means that to keep the ball bouncing, players must continually put more energy into the ball. In this sports science project, you will determine how high a basketball bounces on different surfaces relative to the height from which it was dropped. Which surface enables the basketball to bounce the highest, meaning which requires the least amount of energy from a player to keep on dribbling the ball? Grab a basketball and try this science project idea to find out!

## Objective

Determine how different surfaces affect how high a basketball bounces relative to the height it was dropped from.

## Credits

Teisha Rowland, PhD, Science Buddies

### MLA Style

Science Buddies Staff. "Bouncing Basketballs: How Much Energy Does Dribbling Take?" Science Buddies. Science Buddies, 17 Dec. 2014. Web. 25 June 2017 <https://www.sciencebuddies.org/science-fair-projects/project_ideas/Sports_p037.shtml?from=Blog>

### APA Style

Science Buddies Staff. (2014, December 17). Bouncing Basketballs: How Much Energy Does Dribbling Take?. Retrieved June 25, 2017 from https://www.sciencebuddies.org/science-fair-projects/project_ideas/Sports_p037.shtml?from=Blog

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Last edit date: 2014-12-17

## Introduction

Bounce, bounce, swish! Playing a game of basketball is hard work, and one part of that workout comes from just dribbling the ball. In Figure 1 below, you can see Kobe Bryant, playing on the U.S. men's Olympic team, dribbling a ball. Why does it take effort to dribble the ball? When a basketball hits the ground (and as it flies through the air), it actually transforms some of its energy to another form. If players do not put enough energy back into the ball, they will not be able to dribble it effectively.

Figure 1. When a player dribbles a basketball, as Kobe Bryant does here on the 2012 U.S. men's Olympic team, the ball actually transfers some of its energy on each bounce (Airman 1st Class Daniel Hughes, 2012).

When a basketball bounces, it has two different types of energy: kinetic energy and potential energy. Kinetic energy is the energy an object has due to motion. Any object that is moving has kinetic energy. A fast-moving basketball has more kinetic energy than a slow-moving basketball. And a basketball that is not moving at all has no kinetic energy. Potential energy is the energy stored in an object due to its height above the ground. (A basketball resting on the floor has no potential energy.) For example, when you hold a basketball at waist level, it has some potential energy. If you hold it higher, such as up over your head, it has even more potential energy. If you drop the basketball, the force of gravity pulls it down, and as the ball falls, its potential energy is converted to kinetic energy. As the ball approaches the ground, its potential energy decreases. But the ball also speeds up, so its kinetic energy increases.

So what do kinetic energy and potential energy have to do with how a basketball bounces on the court? As mentioned earlier, when the basketball hits the court's floor, it appear to "lose" some energy—what really happens is that some kinetic energy gets converted into energy in the form of sound, heat, and briefly changing the shape of the ball (flattening it slightly). Some of the energy is also absorbed by the court's surface. When a collision occurs where kinetic energy is lost, it is called an inelastic collision. (On the other hand, an elastic collision is when kinetic energy is conserved—it is the same before and after the collision.) When a basketball bounces (without being pushed down), it does not go all the way back up to its original height, as shown in Figure 2 below. This is because the basketball had an inelastic collision with the ground. After a few bounces, it stops bouncing completely. The energy has left the ball!

Figure 2. A bouncing ball has both kinetic and potential energy. As it bounces, it loses kinetic energy, so each bounce is not as high as the one before it. (Michael Maggs and Richard Bartz, 2007)

One factor that can affect the basketball's inelastic collision with the ground is the type of surface the ball collides with. The surface affects just how much kinetic energy is "lost," or transformed (technically the law of conservation of energy states that energy cannot be lost, but it can change form) and this determines how much energy a player has to put back into the ball to keep it bouncing. In inelastic collisions, different surfaces absorb different amounts of energy. How do you think a hard surface, like concrete, absorbs energy compared to a soft surface, like carpet? In this sports science project, you will determine how high a basketball bounces on different surfaces relative to the height from which it is dropped. Which surface will absorb the least amount of energy and allow the basketball to bounce the highest? Grab a basketball and get ready to find out!

## Terms and Concepts

• Energy
• Kinetic energy
• Potential energy
• Gravity
• Inelastic collision

### Questions

• In a typical game of basketball, when does the ball have more kinetic energy than potential energy and vice versa?
• Why does a basketball eventually stop bouncing if you just let it go and do not dribble it?
• What examples of inelastic collisions have you seen? How is the energy transformed?
• What surface will absorb more energy, a soft or hard one? Why?

## Bibliography

To find out more about kinetic energy, check out this webpage:

This webpage has additional information on elastic and inelastic collisions:

This article discusses some of the physics of dribbling a basketball:

For help creating graphs, try this website:

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## Materials and Equipment

• Different surfaces to bounce a basketball on (at least 3). They should be steady, fixed surfaces. Some examples include carpet, concrete, grass, linoleum, and a basketball court. The surface needs to be flat and next to a wall or other large surface perpendicular to it. Pick at least one hard surface and one soft surface.
• Tape measure, metric
• Painter's tape. This is available at hardware stores or online through sellers such as Amazon.com.
• Video camera. A video camera on a cell phone should work fine.
• Optional: Note cards, index cards, sheets of paper, or something else to write trial numbers on (10).
• Volunteer to videotape the experiments, or a tripod. If you use a tripod, you will need a surface nearby, such as a chair, to set the tripod and camera on. GorillaPods are an example of inexpensive, small types of tripods available through Amazon.com.
• Access to a computer or large screen to watch your recorded videos on
• Lab notebook

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## Experimental Procedure

### Videotaping the Basketball Bounces

1. Prepare the wall, or other vertical panel, next to the first surface you want to test so that you can measure the height of the basketball's bounce.
1. On the wall next to the surface, use a tape measure and the blue painter's tape to mark every 20 centimeters (cm), starting from the floor and going up to 100 cm. You should end up with five tape marks, as shown in Figure 3.
2. Note: You can make the tape marks longer than the ones in Figure 3, so they will be easier to see in the video recording. Remember to put the top edge of the tape at the every 20 cm mark.

Figure 3. On a wall or other panel next to the surface you want to test, place strips of painter's tape every 20 cm, starting from the floor and going up to 100 cm. The test surface shown here is linoleum, and the tape was placed on a refrigerator.

1. Set up the video camera so that all of the marked measurements and the floor are in view. It is best to record the bounce as straight on, or as evenly framed in the viewfinder, as possible. You can either have a volunteer run the camera for you, or set the camera up on a tripod.
1. Tip: If you use a mini tripod, you need a raised surface nearby, such as a chair, to set the tripod and camera on.
2. Test the basketball on the surface:
1. Either ask your volunteer to start the video camera or, if you do not have a volunteer, begin recording with the video camera on its tripod.
2. If you are using note cards to visually keep track of your trials, show a note card with the trial number written on it in front of the camera briefly, before you do the experiment. Alternatively, you can just say the trial number so you can hear it later on the recording. (The first trial you do will be Trial 1.)
3. Hold the basketball so that the bottom of it is lined up with the top edge of the highest tape mark you made, as shown in Figure 4. Also hold the ball close to the wall, not more than about 5 cm away.
1. Make sure your body is not blocking the camera's view of the basketball and the tape-marked wall.
2. Tip: If you have a volunteer helping you, ask them to check if the bottom of the basketball looks lined up with the top edge of the tape mark when looking through the camera.
4. Drop the basketball. (Do not push it down.)
5. Let the basketball bounce back up and then hit the ground a second time before you catch it in your hands and stop recording it.

Figure 4. To record the basketball's bounce, hold it so that the bottom of the ball is lined up with the top tape mark, at 100 cm, before dropping the ball.

1. Repeat step 3 at least nine more times with the surface you just tested, for a total of at least ten trials of this surface.
1. If, in any of the trials, it looks as if the ball did not bounce straight back up, but went slightly to the side, then do an additional trial.
2. Repeat steps 1 to 4 with the other surfaces you wanted to test.
1. You need to test at least three surfaces total, including at least one hard and one soft surface. The surfaces you test should all be flat.
2. For consistent results, try to hold the basketball for each trial the same distance from the wall and also position the camera at the same approximate height (keeping the camera and tripod placed on the same chair and then moving the chair to the new surface is a good way to do this).
3. Note: If you are testing a surface that is at a very different temperature (such as concrete outside on a cold day), you will want to do your trials quickly so that the ball does not change temperature. A change in the ball's temperature can affect how it bounces. You could try doing one trial at a time and bringing the basketball inside in between the trials to let it warm back up.

### Analyzing Your Results

1. Once you have finished testing the surfaces, make a data table in your lab notebook similar to Table 1. You will record your data in this data table. Table 1 has already been partly filled in as an example — fill in the exact surfaces you tested in your own data table. For each surface, describe how hard it is in the "Hardness" column. See examples in Table 1.
 Surface Hardness Drop Height (cm) Bounce Height (cm) Height Difference (cm) Average Height Difference (cm) Trial 1 Carpet Soft Trial 2 Trial 3 etc. Trial 1 Wood Hard Trial 2 Trial 3 etc. Trial 1 Concrete Very Hard Trial 2 Trial 3 etc.

Table 1. In your lab notebook, make a data table like this one to record your results.

1. Now watch your videos closely and fill in the "Drop Height (cm)" and "Bounce Height (cm)" columns in your data table with your results. Watch your videos on a computer or other large screen so you can make detailed observations. Because the actual drop heights and bounce heights will vary slightly from trial to trial, you need to determine them by examining the video carefully.
1. Watch the videos for each trial using slow motion and/or pause the recording right before the basketball is dropped, and then when it is at the highest point in its first bounce.
1. Right before dropping the ball, it is at its drop height.
2. When the ball is at its highest point in its first bounce, it is at its bounce height.
2. Do your best to use the tape marks on the wall to help you estimate the drop height and the bounce height.
3. Always measure the drop height and the bounce height from the bottom of the basketball.
4. The drop height should be close to 100 cm, but you should review the videos to see if it was actually a little above or below 100 cm. For example, in one trial it might have been at about 105 cm, whereas in another trial it could have been closer to 95 cm.
5. Do not count any trials where it looks as if the basketball did not bounce straight up, but instead went off to the side.
2. Calculate the height difference for each trial and note it in your data table. To calculate the height difference, subtract the bounce height from the drop height.
1. For example, if your drop height was 105 cm and your bounce height was 60 cm, your height difference would be 45 cm (since 105 cm - 60 cm = 45 cm).
3. Calculate the average height difference for each surface and record this in your data table. Do this by calculating the average height difference for all of the trials for a given surface.
1. For example, if your height difference for ten trials with a surface were 60 cm, 63 cm, 65 cm, 64 cm, 61 cm, 60 cm, 60 cm, 65 cm, 63 cm, and 62 cm, your average height difference for that surface would be 62 cm (the sum of these numbers divided by ten, since there were ten trials).
4. Make a bar graph of the average height difference for each surface.
1. Put the name of the surface on the horizontal axis (x-axis) and the average height difference (in cm) on the vertical axis (y-axis).
2. You can make the graph by hand or use a website like Create a Graph to make a graph on the computer and print it.
5. Look at your data and your graph and analyze your results.
1. How high did the basketball bounce relative to its drop height when dropped on the different surfaces? Which surface enabled the ball to retain the greatest height relative to the drop height, and bounce the highest? Which surface caused the ball to lose the most height?
2. Based on your results, which surface do you think absorbed the least amount of energy from the basketball, enabling the ball to bounce the highest?
3. Can you use your results to help explain why a basketball court has the surface that it does?

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## Variations

• Try this science project again, but instead of investigating different surfaces, try bouncing a basketball at different temperatures. You could try storing a basketball in a refrigerator or freezer, and then bouncing it. Compare its bounce height to a basketball that was stored at room temperature. How do the bounce heights compare when the basketball is at different temperatures? Tip: Be sure to do the experiments quickly after removing the basketball from the refrigerator or freezer, because the basketball will quickly warm up again.
• You know that a basketball loses kinetic energy by transferring it to other forms when the ball bounces, but just how many bounces can a basketball make before losing all of its kinetic energy and stopping bouncing? And how does this change if you alter some factors, such as the surface the basketball bounces on or the drop height? Design an experiment to investigate how many bounces a basketball can make and how various factors affect that number. You will also want to measure how high each consecutive bounce is. You could then make a graph of bounce height versus bounce number. Give it a try!
• How do different balls bounce compared with each other? You can try this science project again, but just pick one surface to test and try a variety of different types of balls, such as bouncy balls, soccer balls, tennis balls, and others.
• How does a punctured basketball (or soccer ball) bounce compared to one that is not punctured? Try this science project again, but pick one surface to test and first try a ball that is not punctured, then puncture the ball and try it again.
• When the basketball hits the ground, energy is transferred to the floor, converted in the form of heat and sound. Design an experiment to investigate one (or more) of the other ways that kinetic energy can be lost by changing to another form of energy, such as by measuring how loudly the ball hits the ground, or how much the ball heats up. Does the surface the ball is bounced on affect how the energy is lost?
• There are equations you can use to actually calculate potential energy and kinetic energy. You can use Equation 1 below to calculate the potential energy of the basketball when you drop it. You could try measuring the bounce height of the basketball when it is dropped from different heights (but always on the same surface) and calculate how much potential energy it has each time it is dropped. How does its potential energy change when you change its drop height? How does this affect its bounce height? How much energy is transformed on each bounce?

Equation 1:

• PE = potential energy (in joules [J])
• m = mass of the basketball (in kilograms [kg])
• g = acceleration due to gravity, which is 9.81 meters per second squared (m/s²)
• h = height (in meters)

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