# Centripetal Force

"I like work: it fascinates me.  I can sit and look at it for hours.  I love to keep it by me: the idea of getting rid of it nearly breaks my heart”
Jerome K. Jerome – Three Men in a Boat (1889)

• We have already seen that for uniform circular motion the magnitude of the acceleration is given by v2/r

With a directed towards the center of the circle and v tangential (perpendicular to a)
• The force acting on a body of mass m moving in uniform circular motion is given by

directed towards the center of the circle
• The net force acting towards the centre of a circle, keeping the object moving in circular motion, is known as the centripetal force,

e.g.   Gravitational force keeps the Earth in orbit around the Sun.

The tension in a string keeps a rotating object from flying off
•  Be careful.  The centripetal force is NOT a force to be included on a free body diagram.  Rather, the net force towards the center of the circle should be set equal to Fc (= mv2/r = ma).
• Combining your knowledge of frictional forces with centripetal force allows us to solve problems concerning the banking of curves applicable in highway design.

“ It’s true that hard work never killed anybody, but I figure why take the chance ?”

Ronald Reagan – Interview The Guardian (1987)

Dr. C. L. Davis
Physics Department
University of Louisville
email: c.l.davis@louisville.edu