Centripetal Force

• Force, acceleration and velocity are vectors, so they have a direction too.
• When the moon travels around the earth, it's velocity vector is always perpendicular to the earth. (If gravity stopped it would just shoot off along that vector).
• When an object is traveling at a constant velocity (v) around a circle with radius r, the vector changes direction (but not magnitude).
• The force that keeps it on this circle is is called centripetal force.
• F = mvv/r
• The direction is always toward the centre of the circle.