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# Toys and Gravity: How Does Gravity Affect Playing Paddle Ball?

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Source:
Author: Janice VanCleave

### Problem

How does gravity affect playing paddle ball?

### Procedure

1. Hold the paddle in one hand and the ball in the other hand.
2. Pull the ball straight out from the paddle as far as your outstretched arms or the elastic will allow.
3. Release the ball.
4. Observe the path of the returning ball.
5. Again pull the ball straight out from the paddle as far as your outstretched arms or the elastic will allow. Raise the ball up about 1 foot (30 cm) from its horizontal position.
6. Release the ball and observe its path.
7. Continue to change the position of the ball until its returning path directs it to the center of the paddle.

### Results

The returning ball misses the paddle when it is stretched straight out from the paddle. Holding the ball at a height higher than the top of the paddle results in the ball striking the center of the paddle.

### Why?

The string pulls the ball toward the paddle, but gravity pulls the ball toward the center of the Earth, which is straight down. These two forces cause the ball to continue to fall and at the same time move toward the paddle. The result is that the ball moves in a curved path that arches downward. When pulled straight out, the ball's curved path brings it lower than the paddle's handle. The raised ball still moves in a curved path that arches downward, but the new path ends in the center of the paddle.

### Let's Explore

How far does the ball drop before reaching the paddle? The diagram illustrates a method for determining this distance. The paddle is partially covered with black paper and the ball dipped in flour. The ball is pulled straight out from the paddle and released. A white spot on the black paper marks the point of the returning ball. Science Fair Hint: The paddle and paper can be attached to the project display and used to demonstrate the effect of gravity on the toy.

### Show Time!

1. Does gravity make a SlinkyTMslink? Place the toy on the top step of "stairs" made by stacking books, and give it a slight push forward. Observe the movement and direction of the Slinky. Can it be made to climb up the steps? (NOTE: A metal Slinky will give the best results.) Photographs and a written description of the results can be displayed.
2. Does the height of the steps affect the movement of the Slinky? Build steps of different heights with books. Test the Slinky's movement at different heights. Display the record of each height used and the resulting movement of the toy.
3. Collect and display toys that need gravity to work. A short explanation about how each toy works with the help of gravity should accompany each toy.

### Check it Out!

How would toys that depend on gravity behave in space? NASA has tested the behavior of these toys in space: paddle ball, Slinky, yo-yo, ball and jacks, flip toy, wind-up car, paper airplane. Predict and record how you think the toys might behave in space. Remember that in orbiting spacecraft, the pull of gravity is so weak that objects are virtually weightless. Then, find out how these toys actually behaved in space, and compare this data with your predictions. Your teacher can secure a videotape from NASA showing the actual testing of these toys during a space mission.