Objects moving in a circular path have a constant linear velocity but are constantly accelerating because their direction of motion is continuously changing. Centripetal acceleration points toward the center of the circle and depends on an object's speed and the radius of the circle. For an object to travel in a circular path, a net centripetal force pointing toward the center of the circle must be applied to overcome the object's inertia. Examples of circular motion include boats on waves, objects on strings, orbital motion of planets, and the rotation and revolution of Earth.

1. Circular Motion

2. Circular Motion
• Objects moving in a circle still have a
linear velocity = distance/time
• MUST have a constant velocity or would fall
inward or outward
• As object moves around circle, direction of
motion is constantly changing
– Therefore:
• velocity is constantly changing
• constantly accelerating

3. Centripetal Acceleration
• Acceleration of an object moving in a circle points
toward the center of the circle
• This is called a centripetal (center pointing)
acceleration
• The centripetal acceleration depends on:
– speed of the object
– radius of the circle
Fcent
v

4. Centripetal Force
• Newton’s Second Law says that if an object is
accelerating, there must be a net force on it
– this is called the centripetal force
• The centripetal force points toward the center of
the circle
• Centripetal Force

5. Objects Move
• Anything that carries energy moves with
circular motion
• If a boat is floating in the water and a wave
passes underneath it, does the boat change
position?

6. • When the string breaks after an object was
traveling with circular motion , it moves away
in a straight line

7. Orbital Motion
• If the axis of rotation is inside the object, the
object is rotating (spinning)
– Earth rotates on it’s axis
• If the axis of rotation is outside the object, the
object is revolving
– Earth revolves around the Sun
• Which is faster?
– Depends on speed of object & distance traveling

8. Circular Motion Examples
• Which way is the Force?.
• Earth around Sun