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Race of rolling bodies
Intermediate
Solid sphere beats disc, which beats ring.
On an incline the solid sphere beats the disc, then the hollow sphere, then the ring. A sliding block beats all of them.
Experiment: cans of soup rolling.
Winners don't depend on mass or size.
In more detail
Rolling bodies on an incline race according to how their kinetic energy is shared. Solid spheres beat hoops, and both beat sliding blocks, since less energy goes into rotation.
Real-world uses
- Physics demonstrations race cylinders, hoops and spheres down ramps.
- Rolling speed comparisons help explain the design of toys and equipment.
- A classic demonstration races a solid sphere, a disc and a hollow ring down a ramp, and the order follows their moments of inertia.
Open the interactive lesson, with simulation and quiz →
Frequently asked questions
Why does a sliding block win?
Because all its energy goes into translation, with no rotation, so it reaches the bottom fastest.
Which rolling object is slowest?
The hoop, because its moment of inertia is largest.
Which object wins the race?
The solid sphere, which has the smallest I/mR² and so puts the largest share of its energy into translation.
Related topics in Rotational Motion
Rotational kinetic energy · Rolling without slipping · Rolling down an incline · Work and power in rotation · Angular momentum of a particle · Angular momentum of rigid body