Lesson · P.2.3

Rotation and circular motion

Work through why an object moving in a circle is constantly accelerating toward the centre, the two formulas the HESI A2 physics subtest uses for centripetal acceleration and centripetal force, and how linear speed depends on radius at a fixed rotation rate.

ObjectiveP.2.3Read4 minExam weightForces and Newton’s Laws ≈ 20% of Physics

This lesson is part of the full Study Guide

Unlock every lesson, unit, and quiz across every subject. The Physics forces and newton’s laws unit is included.

See editions and pricing →

What you will be able to do

Calculate the centripetal acceleration of an object moving at a known speed around a known radius
Calculate the centripetal force needed to hold an object on a circular path
Explain why a point farther from the centre of a rotating object moves at a higher linear speed at the same rotation rate

What the lesson concludes

Centripetal acceleration points toward the centre of the circle, not along the direction of travel: a_c = v² / r
Centripetal force is the net inward force that holds an object on a circular path: F_c = m × v² / r
Centripetal force is not a new kind of force, it is whatever real force, tension, friction, or a rotor wall, happens to point toward the centre
At a fixed rotation rate, linear speed is proportional to radius, so a point twice as far from the centre moves twice as fast
Doubling speed quadruples the centripetal force needed, since force depends on velocity squared, not velocity alone