Rolling Motion
Race: cylinder vs sphere down ramp. Builds on Moment of Inertia.
Two identical-looking cylinders sit at the top of a ramp. One is solid, the other is hollow (like a pipe). They have the same mass and radius, and are released at the same time.
Which reaches the bottom first?
The solid cylinder wins! It has less rotational inertia, so more of its energy goes into speed rather than spin.
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Watch solid vs hollow race side by side. Try the sliding comparison too — a sliding block always beats any roller!
a = g sinθ / (1 + I/mR²)
The bigger I/mR², the more energy 'wasted' on spinning, and the slower the object goes
A cue ball slides before rolling — the transition from slide to roll is key to spin shots
Heavier rims slow you down — mass near the edge increases rotational inertia
Lighter wheels improve fuel economy — less energy rotating, more energy moving
“Rolling steals energy from speed. The more mass at the edge, the more it steals.”
Ramp Racer
Race different shapes down a ramp. Compare rollers to sliders and discover the rolling hierarchy.
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Race all 5 shapes: sliding block, solid sphere, solid cylinder, hollow cylinder, hollow sphere. Can you predict the finishing order? Now add friction to the slider — what happens?
The rolling hierarchy is universal: sphere (2/5) > disk (1/2) > hollow sphere (2/3) > ring (1). A frictionless slider always wins because it converts ALL energy to speed.