Centripetal Force Demonstration Kit

Quick Answer: The Centripetal Force Demonstration Kit is a physics practical set for investigating the inward force needed to keep a mass moving in a circle. With a centripetal force kit, learners examine how that force changes with the rotating mass, its speed and the radius of the path, and compare their results with F = mv²/r.

Why Circular Motion Needs an Inward Force

An object moving in a circle is always changing direction, so it is accelerating even at a steady speed. That acceleration points to the centre of the circle, and a force in the same direction is needed to produce it. The force is called centripetal, meaning centre-seeking, and in practice it is supplied by something real, such as the tension in a string, friction on car tyres or gravity acting on a satellite.

A common school version uses a small mass, often a rubber bung, whirled on a cord that runs through a smooth hand-held tube, with slotted weights hanging from the lower end to set the tension. A marker on the cord keeps the radius constant, and timing twenty revolutions gives the period and hence the speed. Other kits use a motor-driven rotating arm. The design of this kit is not described in its title, so the parts supplied should be confirmed before ordering.

Whichever design is used, the relationships are the same: doubling the mass doubles the force needed, doubling the speed needs four times the force, and a smaller radius at the same speed needs a larger force. Those patterns explain banked race tracks, spin dryers and the orbits of moons.

Specifications

Applications

• Verifying that centripetal force is proportional to the square of speed
• Plotting force against the inverse of radius at constant speed
• Explaining satellite orbits, banked roads and fairground rides
• Correcting the common belief that circular motion pushes objects outward

Care & Handling

• Check the cord, knots and any rotating mass for wear before each lesson, and replace frayed cord at once.
• Clear a wide circle around the student operating the kit and have observers wear eye protection.
• Keep rotation speeds moderate; good results come from steady timing, not high speeds.
• Store the cord untangled and keep small masses in their container so none are lost.

Why Choose LabEquip

Physics teachers at senior secondary and college level buy this kit for the circular motion topic, where a hands-on measurement makes v²/r far more convincing than a derivation alone. LabEquip supplies it through the STEM kits range, and the Loop-the-Loop Physics Model shows the same force at work on a rolling ball. Send questions through the contact page.

Frequently Asked Questions

Is centrifugal force real?

Seen from the ground, there is no outward force on the rotating object; there is only the inward centripetal force. The outward push a passenger feels on a turning bus is their own inertia, the body trying to continue in a straight line. Centrifugal force appears only as an apparent force when working in a rotating frame.

What happens if the cord breaks or is released?

The object stops accelerating towards the centre and moves off in a straight line along the tangent to the circle at that instant. It does not fly directly outward. This is a simple, memorable way to show that the cord was supplying the centripetal force.

How does speed affect the force needed?

The force is proportional to the square of the speed. Doubling the speed at the same radius needs four times the force, and tripling it needs nine times. This is why sharp bends are far more dangerous at high speed.

How is speed measured in this experiment?

Time a number of complete revolutions, often twenty, and divide to get the period. The speed is the circumference of the circle, two pi times the radius, divided by the period. Timing many turns reduces the effect of reaction time on the result.

Why must the radius be kept constant?

The force also depends on radius, so if the radius drifts during a trial, two variables change together and the results cannot be compared. A marker on the cord or a fixed arm length keeps the radius steady while speed or mass is varied.

What safety precautions are needed?

Use a clear area, keep observers outside the circle of rotation and wear eye protection. Check that the rotating mass is firmly attached, never swing it near the face, and stop at once if the cord starts to fray.

Last Updated: September 2026