Demos: 1M-03 Triple Chute
This demonstration illustrates that the motion resulting from a change in gravitational potential energy is path independent. Identical steel balls roll from the same vertical height down three ramps of different shapes. Friction is negligible and the normal force does no work on the ball. So the speed at the bottom of each ramp is the same. Because the speeds are the same, each ball has the same horizontal range and will enter the slot in the box.
Directions: Check the ramp for level before starting. Place a ball on the first ramp directly over the mark. Release the ball and note that it lands in the box after passing through the slot. Do the same for the other two ramps, making certain that the ball is over the mark before releasing it. Each ball should pass through the slot into the box.
Suggestions for presentation: Ask the students what will happen. Be a little dramatic in suggesting that each path is clearly different from the others. Tell them, however, that the mass of the balls and the relatively small amount of rolling friction prevents friction from playing a significant role.
Applications: Relate this demo outcome to other situations, all of which show that the change in potential energy is independent of path, but it is only when gravity is the only agent doing work that the SPEEDS are the same.