Circular Motion: Chapter 5
Quick notes
5-1
5-2
5-3
1. Uniform motion is when an object moves in a circle with a radius of r at
constant speed.
2. The magnitude of the velocity remains constant while the direction of the
velocity constantly changes meaning the object is accelerating.
3. Radial acceleration is when acceleration is directed toward the center of a
circle and has the magnitude of: ar = v2/r
4. The velocity and acceleration vectors constantly change but are always
perpendicular to one another around the circle.
1. Net force must be acting upon an object to keep it in centripetal motion.
2. The direction of this force is towards the center of the circle.
3. Centripetal force describes the direction of the net force needed to keep the
object on its circular path and must be applied by other object (a string,
gravity, or a normal or electrical force.
4. There is no such thing as centrifugal force (outward center fleeing force).
There is no outward force on the object. The object only reacts to the inward
pull by the force used (the inward pull of the string on the ball)
5. For this reason the ball would fly off tangentially and not straight out.
1. A car going around a curve is undergoing circular motion, even though it is
only part of a circle (an arc).
2. Under normal circumstances, the friction between the tires and the road is
static friction. If the car skids because the road is wet or slippery, the friction
becomes kinetic.
3. The banking of curves (like what you see on a racetrack) can reduce the
chance of skidding. The normal force exerted by a banked road, acting
perpendicular to the road (not to mg), will have a component toward the
center of the circle, thus reducing the reliance on friction.
4. For a given banking angle, there will be one speed for which no friction at all
is required. This is called the “design speed.”
5. Friction is not needed because the horizontal component of the normal force
is exactly equal to the force required for centripetal acceleration,
FN sin  = mv2/r