Centripetal Force Calculator
Work out the centripetal force and acceleration for anything moving in a circle, from a car on a bend to a centrifuge, using F = m v² ÷ r. Enter the speed directly or as RPM, or solve the equation for the speed, radius or mass.
How to use the Centripetal Force Calculator
- Choose what to solve for: force, speed, radius or mass.
- Enter the mass and the radius of the circular path, with their units.
- Enter the speed as a linear speed or as revolutions per minute (RPM) or rad/s.
- Read the force and acceleration, including the g-force.
- Check the table to see how the force grows with the square of the speed.
Centripetal force formulas
| Quantity | With linear speed v | With angular velocity ω |
|---|---|---|
| Centripetal force | F = m v² ÷ r | F = m ω² r |
| Centripetal acceleration | a = v² ÷ r | a = ω² r |
| Speed from force | v = √(F r ÷ m) | ω = √(F ÷ (m r)) |
| Radius from force | r = m v² ÷ F | r = F ÷ (m ω²) |
| Conversions | v = ω r | ω = 2π × RPM ÷ 60 |
Example: a 1,200 kg car on a 50 m radius bend at 50 km/h (13.889 m/s) needs F = 1,200 × 13.889² ÷ 50 ≈ 4,630 N of sideways grip, an acceleration of about 3.86 m/s² (0.39 g).
Where the force comes from
- Car on a flat bend: friction between the tyres and road. With friction coefficient μ the maximum speed is v = √(μ g r).
- Ball on a string: tension in the string.
- Satellite or Moon: gravity, so m v² ÷ r = G M m ÷ r² (see the gravitational force calculator).
- Centrifuge or washing machine drum: the wall of the drum pushes the contents inward. The relative centrifugal force (RCF) is a ÷ g.
The centripetal force does no work on the object, because it is always perpendicular to the motion: it changes the direction of the velocity, not the speed.
Frequently asked questions
What is the centripetal force formula?
Centripetal force is F = m v² ÷ r, where m is the mass, v the speed and r the radius of the circle. Using angular velocity ω (rad/s) it is F = m ω² r. The force always points towards the centre of the circle.
How do I calculate centripetal acceleration?
Centripetal acceleration is a = v² ÷ r = ω² r. Dividing by 9.80665 m/s² gives it in g. A car taking a 50 m radius bend at 50 km/h (13.89 m/s) has a = 13.89² ÷ 50 ≈ 3.86 m/s², about 0.39 g.
How do I convert RPM to speed?
First convert RPM to angular velocity: ω = RPM × 2π ÷ 60 rad/s. Then the linear speed at radius r is v = ω × r. For example 1,000 RPM at a radius of 0.1 m is ω ≈ 104.72 rad/s and v ≈ 10.47 m/s.
What is the difference between centripetal and centrifugal force?
Centripetal force is the real inward force (from friction, tension, gravity or a normal force) that keeps an object on a curved path. Centrifugal force is the apparent outward push felt in the rotating frame of reference. They have the same size, m v² ÷ r.
What happens to the force if the speed doubles?
The force quadruples, because it depends on the speed squared. Halving the radius at the same speed doubles the force. That is why tight corners at high speed need so much grip.
How is a centrifuge's RCF related to RPM?
Relative centrifugal force is the centripetal acceleration in g: RCF = ω² r ÷ g. With r in centimetres this is the familiar RCF ≈ 1.118 × 10⁻⁵ × r × RPM². Enter the rotor radius and RPM here and read the acceleration in g.