CENTER OF MASS

DEMO
Materials: Meter stick, C-clamp

Procedure
Hold the meter stick horizontally between two fingers. Slowly slide your hands together. For a real challenge, close your eyes when sliding your hands together. Your hands will always meet under the center of mass.

Attach a c-clamp at one end of the meter stick. Redo the demonstration. Your fingers will still meet under the center of mass.

CENTER OF MASS OF A ROLLER COASTER TRAIN

The center of mass of a train would be in the center of the train. This is assuming all the riders are of the same mass. The feeling a track is designed for is engineered around the center of mass of a train. A rider gets a different feeling if she is to ride some distance away from the center of mass.

OVER THE HILLS
A hill is designed for a specific velocity. The design velocity is chosen such that the rider located at the train's center of mass will, at most, feel weightless. The hill's shape determines the design velocity. This shape also dictates a specific velocity at each part of the hill.

This can be demonstrated by using the HotWheels™ train. (Click here to go to the construction of the HotWheels™ train.) Set up a box with a track running horizontally over the top. Slowly roll the train over the hill. As the front of the train begins to pass over the hill it will not speed up until the middle, center of mass of the train, travels over the hill.