Why Does a Ball Stop Rolling? A Friction Experiment for Grade 3

Roll a ball across the floor and it eventually stops. Ask children why, and many say, “It ran out of energy” or “It got tired.” The correct answer, that something is pushing back, is a surprise to many, and it’s the heart of Grade 3 forces.

The experiment

Question: Does the surface change how far a ball rolls?

You need: a tennis ball (or another small rubber ball), a ramp (a stiff binder or thick cardboard, about 30 cm long), a stack of books, a carpet sample or rug, a bath towel, a tape measure and masking tape.

Method:

Prop the ramp on the same stack of books every time.
Release the ball at the same mark on the ramp, without pushing.
Let it roll onto a hard floor. Measure how far it travels from the foot of the ramp.
Repeat on carpet and on the towel.
Do three trials on each surface and record them in a table.

What stays the same: the ball, the ramp, the release point and the person measuring. What changes: the surface.

What happens

The ball rolls farthest on the hard floor, less far on carpet, and least on the towel. The ranking is nearly always the same, and the numbers prove it.

The science: friction

When a ball rolls, the surface rubs against it. That rubbing force is friction, and it acts against the direction of motion. Rough, soft surfaces like carpet and towel create more friction than smooth hard floor, so they stop the ball sooner.

If you could remove all friction (and air resistance), a rolling ball would keep rolling at the same speed. That’s what an object does unless a force acts on it, an idea formalised by Isaac Newton as inertia. So the real question is not “why does the ball keep moving?” but “what is stopping it?”

Common mix-ups

“It ran out of push.” Motion doesn’t get used up. A force slows it.
“Friction is always bad.” Without friction you couldn’t walk, grip a pencil or stop a bike.
“Heavier balls roll farther.” Test it. It’s a good follow-up experiment.

Extension ideas

Predict the order for four new surfaces (foil, sandpaper, a yoga mat, a book cover) and test.
Try a different ball (a golf ball or marble) on the same surfaces.
Graph the average distance for each surface.
Ask: where is friction helpful? Where is it a problem?

Our lesson Why does a ball stop rolling? has teams run these tests and explain the result. It’s the first lesson in Pushes, Pulls and Magnets, which continues with magnets and a paper-clip gadget challenge. Sign up for three lessons free.