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Two objects with the same shape and the same mass may behave differently when they roll down a hill. How quickly an object accelerates depends partly on how its mass is distributed. A cylinder with a heavy hub accelerates more quickly than a cylinder with a heavy rim.
Place both tins at the top of the ramp. Be sure the tops are on the tins. Ask your friends to predict which tin will reach the bottom of the ramp first. Release the tins and let them roll down the ramp. The tin with the mass closer to the center will always reach the bottom first.
At the top of the ramp, both tins have identical potential energy, since both have the same mass and are at the same height. At the bottom of the ramp, each tin will have part of its original potential energy appearing as linear (or translational) kinetic energy and the rest appearing as rotational kinetic energy.
Although both tins have the same total mass, each has this mass distributed differently. It’s harder to get the tin with distributed mass (washers pushed up against the outer rim) rotating compared with the tin that has its mass concentrated at the center. The tin with its mass at the rim will use more of its original potential energy just to get rolling. Therefore, it has less energy available to appear as translational kinetic energy, resulting in a lower linear speed. So, the tin with its mass concentrated around the rim will lose the race down the ramp, and the tin with its mass concentrated at the center will win.
The use of lightweight “mag” wheels on cars is related to translational and rotational kinetic energy. Imagine that you had two cars of equal overall mass, but one had lightweight mag wheels and a heavy chassis, and the other had heavy steel wheels and a light chassis. Given the same energy input, the mag-wheel car would accelerate more rapidly, because less of the energy supplied would be needed to get the wheels rotating, and more would therefore appear as straight-line motion of the car as a whole.
It’s also interesting to experiment with rolling cans of soup down an inclined plane. Solid soups roll down the incline at a slower rate than liquid soups. The liquid does not have to rotate with the can, so the potential energy of the liquid soup can go into linear motion, not into rotation of the soup.
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Attribution: Exploratorium Teacher Institute