Circular Motion

 Look at Fig 9.1 pg 122  Why do the occupants of this carnival ride not fall out when it is tipped almost vertical?

 Axis- the straight line around which rotation takes place.  Rotation-when an object turns about an internal axis (located within the body of the object) Also called spin.  Revolution- when an object turns about an external axis. Also referred as revolve about its axis

 Axis- the straight line around which rotation takes place.  Rotation-when an object turns about an internal axis (located within the body of the object) Also called spin.  Revolution- when an object turns about an external axis. Also referred as revolve about its axis

 Does a tossed football rotate or revolve?  Does a ball whirled overhead at the end of a string rotate or revolve?

 Linear speed- distance moved per unit of time (remember Ch.2)  Tangential speed- the speed of something moving on a circular path.  For circular motion, we can use the above terms interchangeably.  Rotational speed- number of rotations per unit of time. (sometimes called angular speed)  All parts of the RIGID merry-go- round rotate about their axis in the same amount of time, thus all parts have the same rate of rotation.

Have you heard of RPM’s??

 Linear speed is the distance per unit of time while rotational speed if the number of rotations per unit of time.  Linear speed varies with the distance from the axis of rotation.  Therefore…if in a circle linear speed is interchangeable with tangential speed we can say the following…

 Centripetal force-any force that causes an object to follow a circular path.  Means ‘center-seeking’  This is not a new force; it is ANY force that is directed at a right angle to the path of a moving object and tends to produce a circular motion.

 Examples of centripetal force  Gravitational force directed toward the center of the Earth holds the moon in an almost circular orbit  Electrons revolving around the nucleus of an atom.  A Centrifuge…what is a washing machine?

Simulated Gravity True Gravitational force is always an interaction between one mass and another. The gravity we feel is due to the interaction of our mass and the mass of Earth. Gravity is simulated by centrifugal force. In a rotating reference frame the centrifugal force has no agent such as mass……there is no interaction therefore it cannot be a TRUE force. Centrifugal force is an effect of rotation. That’s why it is referred as fictitious.