In a baseball game you may have seen a pitcher throwing a curve ball. Have you ever wondered why he does that? In this experiment we will demonstrate how a baseball pitcher throws a curve ball.
Things Required:
Golf ball, or any ball of comparable size and weight
String, 3 ft. (90 cm)
Masking tape
Yardstick (meter stick)
Directions:
Attach the string to the ball with a strip of tape. Tape the free end of the string to the top edge of a table. The ball must be able to swing freely from the table. Lie the yardstick on the floor directly under the ball and pointing in the direction that the ball will be swung.
Twist the string about 50 times in a counter-clockwise direction. Pull the ball and the twisted string back and release it. Allow the ball to swing back and forth. Use the yardstick on the floor to help you observe the direction of the swing.
This Is What Happens:
The ball spins in a clockwise direction as it moves forward. After a few swings, its forward motion curves to the right.
Science Behind It:
The ball is moving in two directions, around on its own axis and forward. These two directions of motion cause air to flow around the ball in two different directions. As the ball spins clockwise, air is carried with the spinning ball in a clockwise direction. Air pushes in the opposite direction when the ball moves forward. Look at the diagram of the top view of the moving ball. Notice that the arrows are pointing in the same direction on one side of the ball. This indicates that the air is moving in the same direction, which causes an increase in the speed of the air on this side. The air currents are moving in opposite directions on the other side and push against one another, forcing the air to move more slowly on that side. Fast-moving air applies less sideways pressure, so the ball has less pressure on the side with the fast-moving air and more pressure on the side with the slow-moving air. The ball curves to the side with less air pressure. To throw a curve ball, a pitcher must spin the ball as he throws it forward. If he spins it clockwise, it will curve to the right, but if he spins it counter-clockwise the ball will curve to the left.
