Shoot the Hoop

Said the acrobat on the trampoline, "I'm feeling very elastic,"
Said the ball to the hoop, "I was aimed to make this basket."

Items You May Need:
measuring tape or ruler
protractor
tape
graph paper
a friend

Challenge: Measuring the angle of the Trampoline

Hint: Place the protractor on long tube and hold it there. Lower your head to the level of the Trampoline, then sight across its bouncing surface to read the angle.

Here's What To Do:

Build the following framework.

You will be able to change the angle of the trampoline by sliding the cross-beam connectors in the tubes back and forth or up and down.

You're done building! Now look at the framework and predict all the possible paths the ball might take. If the ball goes wild, will it break anything? Now is a good time to move the framework to a safe place.

Ask a friend to place a ball in the Ball Drop. When you're both ready, have him or her release it. Where did the ball land? If the ball hits a short tube, you may want to remove it from the framework.

  Height A Height B Height C Height D Height E Height F
Angle Hit

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The object of this activity is to make a basket with the ball drop clipped to 5 or 6 different heights. Start with Height "A" as high as you can get on the framework. Then slide the adjustable supports and ball drop down 3 or 4 inches for each height. Measure from the trampoline to the ball drop and record each height on the Shoot the Hoop Data Table. The trampoline will stay where you have mounted it. However, you can increase your chances of hitting the basket by changing the angle of the trampoline. For example, if Height "A" is 24 inches above the trampoline you might start by setting the angle at 30° above horizontal. Record your hits and misses on the Shoot the Hoop Data table. Then change the angle by 5° and try again. Repeat this process for each height. When you get to the lower heights you may have to move the catch basket closer to the trampoline.

When you have collected data for 5 heights, graph the successful baskets using graph paper. This will help you see the patterns better. You can use the graph to help you predict what will happen when you release the ball from the 2 remaining heights.

The height from which the ball drops determines the ball's speed when it reaches the Trampoline Ball Bouncer. Without enough speed, the angle of the Trampoline Ball Bouncers does not matter - the ball will always fall short. But as you probably discovered, the angle of the Trampoline Ball Bouncer is the key to making baskets.

If the only force applied to the ball after it left the Trampoline Ball Bouncer were a reaction force, then it would be easy to aim the ball. You could just find an angle and shoot the ball straight to the basket. That would work on board the Space Shuttle. (But you would be missing the force that pulls the ball from the Ball Drop to the Trampoline Ball Basin - gravity!) It would also work if you used a beam of light instead of a ball and a mirror instead of a Trampoline Ball Bouncer. Light travels in a straight line unless there is something to change its direction (such as a mirror) or "bend" it (such as a lens). But you're not working with a beam of light, and you're not in space.

Here on the surface of the Earth, gravity is working on the ball before, during, and after it bounces on the Trampoline Ball Bouncer. What happens? In the instant that the ball is in contact with the trampoline, gravity and the reaction force of the trampoline on the ball combine to form a net force. The result of that net force is the path the ball begins to take through the air. When the ball leaves the trampoline, the ball's inertia and the pull of gravity determine its final path. That path looks like an arc, a beautiful, game-winning arc right into the basket.

Build With It!

You can use what you learned from Shoot the Hoop in your own projects. Knowing how the height of the Ball Drop and the angle of the Trampoline Ball Bouncer affect the path of the ball can help you position these stunt pieces in the framework.

Easy Variations:


Add the Elevator. You'll have to add some track. Try aligning the track directly beneath the hole in the Catch Basket. You could also try mounting the catch basket at different levels, above or below the trampoline.

Stage I

Build the setup. Play with the heights and angle of the trampoline. How many baskets can you get in a row?

Stage II

Take a sheet of paper and write down instructions for how to set up the game to always get the ball in the basket. Give it to a friend and without helping let them set up and try it. Did they get a basket on the first try? What instructions were missing from your sheet of paper?

Stage III

From the plot of angle versus height of basket, what would you expect to be required in order to get a basket from twice the height of your current setup?