# Surface Science: Where Does a Basketball Bounce Best?

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## Summary

Key Concepts
Energy, gravity, collisions, sports
Credits
Teisha Rowland, PhD, Science Buddies

## Introduction

Playing basketball can be hard work. Players not only constantly run around the court, but just dribbling the basketball takes effort too. Have you ever wondered why that is? 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 activity, you will explore how high a basketball bounces on different surfaces compared to the height from which it was dropped. Which surface lets the basketball bounce the highest? Grab a basketball and try this activity to find out!

This activity is not recommended for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.

## Background

Playing a game of basketball is hard work, and one part of that workout comes from just dribbling the ball. Why is this? 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.

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. Potential energy is the energy stored in an object due to its height above the ground. For example, when you hold a basketball at waist level, it has some 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. When a basketball hits a court’s floor, 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.

## Materials

• At least two different surfaces to bounce a basketball on, with at least one hard surface and one soft surface. For example, you could use 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.
• Tape measure or yardstick
• Painter’s tape or masking tape
• A helper
• Video camera and access to a computer or a large screen to watch your recorded videos on (optional)

## Preparation

1. Prepare the wall, or other vertical surface, next to the surfaces you want to test so that you can estimate the height of the basketball’s bounce. To do this, use a tape measure or yardstick along with the painter’s tape or masking tape to mark every eight inches, starting from the floor and going up to 40 inches high on the wall. You should end up with five tape marks on each wall.
2. If you are using a video camera, ask your volunteer to set it up so that all of the marked measurements and the floor are in view. When you’re ready to test the basketball on a surface, ask your volunteer to start the video camera.
3. If you are not using a video camera, ask your volunteer to get ready to watch when you drop the basketball to see roughly how high it bounces after it first hits the ground.

## Instructions

1. Hold the basketball so that the bottom of it is lined up with the top edge of the highest tape mark you made.
2. Drop the ball. (Do not push it down.)
3. Let the basketball bounce back up and then hit the ground a second time before you catch it in your hands (and stop recording if you were doing so). How high does your volunteer say the basketball bounced after hitting the ground the first time?
4. Repeat this a few more times, dropping the basketball on the same surface, to give you a good idea of just how high the basketball bounces when being dropped on this surface.
5. Repeat this entire process with the other surface(s) you want to test. How high does the basketball bounce on another surface compared to the first one you tested? Why do you think this is?
6. Tip: 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 testing quickly so that the ball does not change temperature. A change in the ball’s temperature can affect how it bounces.
7. If you videotaped the basketball bounces, watch your videos to try to more closely estimate the basketball’s bounce height on the different surfaces.

Extra: Try to quantify your results from this activity. To do this, you’ll want to videotape your bounce trials and closely watch the videos on a large screen to determine the exact height of the basketball before being dropped, and the highest point in its first bounce. You could even graph your results. Exactly how high does the basketball bounce on the different surfaces?

Extra: You could try this activity 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?

Extra: 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, then try it out!

## Observations and Results

Did the basketball bounce much higher on the harder surface compared to the softer one?

One factor that can affect the basketball’s collision with the ground is the type of surface the ball collides with. When a basketball bounces on a surface, some of its energy is absorbed by the surface. How much energy gets absorbed determines how much energy a player has to put back into the ball to keep it bouncing. A hard surface, like concrete, absorbs less energy compared to a soft surface, like carpet. The more energy that gets absorbed by the surface, the less energy remains in the ball for it to bounce. This is why you should have seen that when the basketball was bounced on a relatively hard surface it bounced higher (it lost less energy) compared to when it was bounced on a softer surface (where it lost more energy). For example, depending on the exact basketball and surfaces, you may have seen the ball bounce about 15 inches high on carpet and about 25 inches high on concrete.