Chapter 9

Circular Motion

• Axis – Central point around which rotation occurs

(axis)

(fulcrum)

• Rotation – occurs when an object turns about an internal axis (earth rotates on its axis, a skater rotates on his/her axis)

• Revolution – occurs when an object turns about an external axis (a satellite in orbit revolves around the earth)

• Linear speed = distance / time

• The linear speed is greater on the outer edge of a rotating object than it is closer to the axis.

• Tangential speed – the direction of motion is always tangent to the circle. For circular motion, linear speed and tangential speed are used interchangeably

• Rotational Speed (angular speed) – is the number of roations per unit of time

Example: revolutions per minute (rpm) of a motor

• Centripetal force - “center-seeking” force that causes an object to follow a circular path

• Centrifugal force - “center-fleeing” force that tends to push objects away from a center of rotation

• Both Centripetal force and centrifugal force depend on the mass, tangential speed, and radius of curvature

The amount of centripetal force that acts on an object revolving around an axis of rotation can be expressed with the following equation:

Fc = mv2

r

• For centripetal and centrifugal force, the magnitudes of each are equivalent.

(read pages 126-132)

Fcentripetal Fcentrifugal