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Circular motion dynamics
Intermediate
Net inward force provides centripetal acceleration.
F = mv²/rFor circular motion, the net force toward the centre is mv²/r. Identify which actual force(s) supply it (tension, friction, normal force or gravity) and set their inward sum equal to mv²/r.
A 0.5 kg stone on a 1 m string at 4 m/s: T = 0.5·16/1 = 8 N.
Centripetal force isn't a new force; it's the name for the net inward one.
In more detail
An object moving in a circle needs a net force directed towards the centre, F = mv²/r. This force is supplied by real forces such as tension, gravity or friction.
Real-world uses
- Satellites stay in orbit because gravity provides the centripetal force.
- A spinning ball on a string is kept in its circle by tension.
- A ball on a string whirled in a circle is held in its path by the tension, which supplies the inward force.
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Frequently asked questions
Is centripetal force a separate force?
No. It is the name for the net inward force, which is provided by other forces.
What happens if the force is too small?
The object moves outward, away from the centre of the circle.
What provides the centripetal force on a car at a bend?
Friction between the tyres and the road, which pushes the car towards the centre of the curve.
Related topics in Newton's Laws & Forces
Variable mass systems · Rocket propulsion · Conservation of momentum · Banking of roads · Vehicle on flat circular turn · Conical pendulum