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Spin the roundabout. How hard must the spring pull to keep the toy going round?
Roundabout Ride lab · Last updated: 16 October 2026
A toy sits on a spinning roundabout, held by a spring to the centre. You spin it faster and watch the spring stretch. The question: how hard must the spring pull to keep the toy going round?
What you'll discover
- Anything moving in a circle needs a pull towards the centre.
- Spinning twice as fast needs four times the pull.
- Without that pull, the toy would fly off in a straight line, not outwards.
The science in plain words
Left alone, a moving object travels in a straight line at a steady speed. That is Newton's first law. To make something go round in a circle, you must keep pulling it sideways, towards the centre. This inward pull is called the centripetal force, which means centre-seeking.
On the roundabout the spring supplies this pull. The faster the roundabout spins, the harder the spring must pull, so it stretches more. The pull needed grows with the square of the speed: double the speed and you need four times the force. A heavier toy also needs more pull, and so does a tighter circle at the same speed.
Many people believe something pushes the toy outwards. In fact, if the spring broke, the toy would sail off along the edge of its circle in a straight line, at a tangent. The outward feeling you get on a fast ride is just your body trying to keep going straight while the seat turns you.
Circular motion is everywhere. Gravity provides the centre-seeking pull that keeps the Moon in orbit, and friction from the road keeps a car on a curve.
Where it fits
- India, NCERT: Class 9 science, Chapter 7: Motion
- United States: Grades 9 to 12
- Next Generation Science Standards: HS-PS2-1
Common questions
What is centripetal force in simple words?
It is any pull towards the centre that keeps something moving in a circle. A string on a swung ball, gravity on the Moon and grip on a car's tyres on a bend are all examples.
Why do you feel pushed outwards on a fast ride?
Your body wants to keep going in a straight line. As the ride turns, the seat pushes you inwards to change your direction, and that feels like being thrown outwards.
What happens if the string breaks when you swing a ball?
The ball flies off in a straight line along the direction it was moving at that instant, touching the edge of the circle, rather than straight outwards from the centre.
Related labs
- Orbital Mechanics: Newton's cannonball: how fast must you fire it sideways so it never lands?
- Rolling Race: Race a ball, a cylinder, a hoop and a hollow ball down a ramp. Which one wins?
- Solar System: A desk orrery run by real gravity: why does Mars take longer than Earth to go round?
See all physics labs or every Taz science lab.
Try it yourself
The Roundabout Ride 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.