SCIENCE CONCEPT: A moving object may collide, perhaps with another object on the move or with an obstacle. As it comes to a stop, the moving object loses its kinetic energy. This energy has to go somewhere. Energy often goes to the other object which may start moving or change the energy it receives into heat. STUDENT OBJECTIVE: The student will explore Newton's Second Law of Motion in relationship to a bouncing ball. OVERVIEW: In Newton's Second Law of Motion the force is defined. When a force acts on an object, the object accelerates in the direction in which the force is acting. A force acting on a stationery object starts it moving. A force acting on a moving object will speed it up, slow it down, or change the direction in which it is moving. In this activity, students will experiment with a ball and see what happens when they bounce the ball on cement and up against a wall. PREPARATION TIME: 5 minutes. LESSON TIME: 25 minutes. TEACHER PREP: Gather balls for the experiment and make sure that you have a safe cement area, along with a wall where the children can bounce the balls. WORDS TO KNOW: collide kinetic energy transfer bounce elastic force accelerates absorb

TEACHER TEXT:
A moving object often collides with another that is free to move, like the balls in a game of pool. As one ball strikes another, it sets the other ball rolling. The first ball transfers kinetic energy to the second ball, which starts to move. It may transfer all its energy, so that the first ball comes to a stop. The second ball then moves off at the same speed as the first ball. If the first ball transfers only part of its energy, both balls continue to move at a slower speed. Kinetic energy is the energy of movement. Everything that moves has kinetic energy because it is moving. When it is moving the amount of kinetic energy depends on the amount of matter and speed of the moving object.

A collision often results in a bounce. In this case, one or both of the objects is elastic, like a rubber ball. An elastic object changes shape when a force acts on it, but regains its shape when the force stops. The ball changes shape as it strikes the ground. Then it regains its shape, which causes it to push against the ground and bounce so that it also regains its kinetic energy.

Not all collisions result in movement. Soft surfaces can absorb motion so that anything striking the surface stops. The objects in the collision absorb the kinetic energy of the moving object. The energy changes into sound (the noise of the collision) and into heat.

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