180
Summary
Selected Vocabulary
uniform circular motion.........circular motion in which the magnitude of the velocity vector remains
constant
nonuniform circular motion...circular motion in which the magnitude of the velocity vector changes
radial......................................parallel to the radius of a circle; the in-out direction
tangential...............................tangent to the circle, perpendicular to the radial direction
Notation
a
r...................................................................
radial acceleration; the component of the acceleration vector along the in-
out direction
a
t....................................................................
tangential acceleration; the component of the acceleration vector tangent
to the circle
Summary
If an object is to have circular motion, a force must be exerted on it toward the center of the circle. There is
no outward force on the object; the illusion of an outward force comes from our experiences in which our point
of view was rotating, so that we were viewing things in a noninertial frame.
An object undergoing uniform circular motion has an inward acceleration vector of magnitude
|a| =
v
2
r
.
In nonuniform circular motion, the radial and tangential components of the acceleration vector are
a
r
= |v|
2
/r
a
t
= slope of the graph of |v| versus t .
Chapter 9Circular Motion