The centripetal force is the force that acts on an object to keep it moving in a circular path. The magnitude of the centripetal force for an object with mass m moving on a circular path (with radius r) at a constant tangential velocity v is given by F_{c}=mv^{2}/rthe equation where centripetal force is equal to mass times velocity squared, divided by radius of the circular path..

**Figure 1:** Schematic of circular movement of an object with mass m

It can be useful to write the centripetal force in terms of angular velocity ωwith a symbol of lowercase omega, which is equal to velocity multiplied by the radius of the path, so that F_{c}=mrω^{2}centripetal force is equal to mass times radius times angular velocity squared. The orbital period is given by T= 2π/ωperiod being equal to 2 times pi divided by angular velocity, so the centripetal force can be expressed as F_{c}=mr(2π/T)^{2}centripetal force equal to mass times radius times 2 pi divided by orbital period squared.

The centripetal acceleration (following Newton's second law of motion) is given by v^{2}/r velocity squared divided by the radius and radially directed towards the center of the circular path.

As follows from F_{c}=mr(2π/T)^{2}the equation for centripetal force being equal to the mass times radius times 2 pi divided by orbital period squared, the centripetal acceleration of e.g. a satellite can be calculated when the radius and the period T are given. Knowing the distance of the moon from the earth and the time it takes the moon for one round-trip, Newton calculated the centripetal acceleration of the moon from which he deduced the inverse square law of gravitation.