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Race a ball, a cylinder, a hoop and a hollow ball down a ramp. Which one wins?
Rolling Race lab · Last updated: 16 October 2026
Four shapes line up at the top of a ramp: a solid ball, a solid cylinder, a hoop and a hollow ball. You predict the winner, let them go and watch the race. The result surprises most adults too.
What you'll discover
- The solid ball wins, and the hoop comes last, whatever their weights.
- Shapes with more mass near their rim are harder to spin up, so they roll more slowly.
- A rolling object shares its energy between moving forward and spinning.
The science in plain words
When something slides down a ramp without friction, all the energy it gains from going down goes into moving forward. Rolling is different. A rolling object must also spin, and spinning takes energy too. So the energy from the drop is shared between moving forward and turning round.
How much goes into spinning depends on where the mass sits. In a hoop, all the mass is out at the rim, far from the centre, which makes it hard to set spinning. A big share of its energy goes into the spin and less is left for speed down the ramp. In a solid ball, much of the mass is close to the centre, so spinning is easy and more energy is left for forward speed.
This resistance to spinning is called the moment of inertia. The order of the race is solid ball, then solid cylinder, then hollow ball, then hoop. Remarkably, size and weight do not matter: a small hoop and a large hoop tie, because both have all their mass at the rim.
Engineers use this idea when designing wheels, flywheels and even figure skaters' spins.
Where it fits
- India, NCERT: Rolling and moment of inertia go beyond the NCERT syllabus for classes 6 to 10; the lab builds on kinetic and potential energy in Class 9 Chapter 10: Work and Energy.
- United States: Grades 9 to 12
Common questions
Which rolls down a ramp fastest, a ball or a hoop?
A solid ball beats a hoop every time. The hoop has all its mass at the rim, so more of its energy goes into spinning and less into speed down the slope.
Does a heavier ball roll down a ramp faster?
No. Two solid balls of different weights roll down together, because both their pull from gravity and their resistance to spinning grow in the same proportion with mass.
What is moment of inertia?
It measures how hard it is to start or stop something spinning. It depends on how far the mass is from the centre: mass at the rim makes it large, mass near the middle makes it small.
Related labs
- Slide and Light Gates: Let a toy sled slide down a slide. How fast does it pick up speed?
- Gear Mechanisms: Big gear, small gear: which one turns faster, and why?
- Roundabout Ride: Spin the roundabout. How hard must the spring pull to keep the toy going round?
See all physics labs or every Taz science lab.
Try it yourself
The Rolling Race lab is one of the interactive 3D science labs inside Taz. Change one thing, predict what will happen, then run it and watch. Labs open after you sign in.