| The focus of this chapter is on uniform
circular motion, objects moving in a circle constant speed (number of revolutions
per time does not change). However, the velocity is always changing because the
object is always changing direction as it travels. since the velocity is always
changing, that means the object is accelerating (even though its speed is constant).
This special type of acceleration is centripetal or radial acceleration, and is
defined as: ac = v2/r
the centripetal acceleration vector always
points to the center of the circular path; the velocity points in the direction of
movement (tangent to the circular path. The result is that the acceleration and
velocity vectors are perpendicular to each other:
Circular motion also demonstrates that
acceleration does not always have to be in the same direction or in the same plane as
velocity.
Recall Newton's 2nd law applies to circular
motion, it says that if a body of mass m is accelerating, it must be experiencing a net
force given by F = ma. Which direction does the net force act? Net force
produces an acceleration in the direction of the net force; therefore, the force acts
toward the center of the circular path.
Fc = mac = mv2/r
This is the net force required to
centripetally accelerate an object in a circular path with a radius of r.
Then why, when you release an object swung in
a circular path, does it fly outward? It takes a net force (the resultant of all
forces) acting inward that keeps the object spinning in a circle; if you let go, the net
force is no longer inward, so the object flies outward. |
