Chapter 9 Circular Motion

Axis: The straight line about which rotation takes place

Rotation: Spin, when an object turns about an internal axis

Revolution: when an object turns about an external axis

• Linear Speed: change in distance/time

• Tangential Speed (v): the speed of an object moving in a circular path is always tangent to the circle.

Rotational Speed or angular speed():

• number of rotation/ time

• Tangential speed is directly proportional to the rotational speed and the radial distance from the axis of rotation (r).

– What does this mean????

Tangential Velocity = (radius)(rotational Speed)

• As an equation: v = r

Important Equation for a Circle

• Circumference = 2r

• Knowing this, you can solve for– the distance a circular object will move in one

rotation– The number of revolutions a circular object will

travel in a set distance

• Frequency (f): Number of times an event occurs in a given unit of time– Units: s-1 or Hertz– Example: 80 beats/60 sec

• Period (T): The time it takes to complete 1 cycle– Example: 0.75 sec between beats

f = 1/T and T = 1/f

V = 2r/T

• Linear Speed for a given point on a circular path is given by Circumference divided by the period.

V = 2r/T

• Linear Speed for a given point on a circular path is given by Circumference divided by the period.

Example: Identify the linear speed of an object that is 0.1 m from the center of its spin and makes 1 rotation per second.

V = 2r/T

• Linear Speed for a given point on a circular path is given by Circumference divided by the period.

Example: Identify the linear speed of an object that is 0.1 m from the center of its spin and 1 rotation takes 1.5 sec.

V = 2(0.1 m ) / 1.5 sec = 0.42 m/s

Centripetal Force:

• Any force that causes an object to travel in a circular path.

• The force is directed at a right angle to the path of movement.

Centrifugal Force:

The outward “force” of circular motion

Simulated Gravity

Where F = 9.8 m/s2

You are able to solve for the radius (r) and/or velocity (v) needed for a particular mass to experience the force of gravity!

Ch9. part 2, then finish the lab from Ch. 8!