Download 1 circular motion

Circular Motion
Q: What makes you dizzy on a rollercoaster ride?
Uniform Circular Motion
Uniform circular motion is motion along a circular
path in which there is no change in speed, only a
change in direction.
Fc
v
Velocity v tangent
to path.
Centripetal force Fc
toward center.
Q: What is the direction
of acceleration?
ac is directed toward center.
Uniform Circular Motion
1. Is there an outward force acting on the ball?
No, the so called centrifugal force does not exist.
2. How does the ball move if the string breaks?
v
Ball moves along the tangent
to path, NOT outward as
might be expected.
When centripetal force Fc is
removed, ball continues in
straight line.
Centripetal force Fc is needed to change direction.
A Car on an Exit
You are sitting on the seat next to
the outside door. What is the
direction of the resultant force on
you as you turn? Is it away from
center or toward center of the turn?
• Car going around a
curve.
Fc
Force ON you is toward the center.
A Car on an Exit (continued)
Reaction
Fc
F’
The centripetal
force is exerted
BY the door ON
you. (Centrally)
There is an outward force, but it does not act ON
you. It is the reaction force exerted BY you ON
the door. It affects only the door.
“Gravitron” at the Fair
Disappearing
platform at fair.
r
Fc
What exerts the centripetal force in this
example and on what does it act?
The centripetal force is exerted BY the wall ON
the man. It is the normal force. A reaction
force is exerted by the man on the wall, but
that does not determine the motion of the
man. It acts on the wall.
Spin Cycle on a Washer
How is the water removed
from clothes during the spin
cycle of a washer?
Does the centripetal force throw
water off the clothes?
NO. Actually, it is the LACK of a force that
allows the water to leave the clothes through
holes in the circular wall of the rotating washer.