Circular MotionCircular Motion

Uniform circular motion: examples include Uniform circular motion: examples include •Objects in orbit (earth around the sunObjects in orbit (earth around the sun•Driving a car around a cornerDriving a car around a corner•Rotating a ball around on a stringRotating a ball around on a string

Circular MotionCircular Motion

• According to Newton’s mechanics, objects don’t tend to move in a circle by themselves. They tend to either be at rest of move in a straight line at constant speed (this is Newton’s first law)

Circular MotionCircular Motion

• Circular motion is not “natural” motion

• Some (a Force) must make an object move in a circle

• The Force causing circular motion can be one of many different forces, depends on the situation (orbit = gravitational force, car turning a corner = frictional force, ball on a string = tension force)

Circular MotionCircular Motion

• Remember from Newton’s 2nd law, that …..Force = mass x acceleration (F = ma)

• But if the object is in uniform circular motion, their speed is constant, so is acceleration = 0?

Circular MotionCircular Motion

• In circular motion, the acceleration is a change in the direction of the object, even though the speed is constant, the direction keeps changing, and velocity is a vector.

• The force keeps pulling the object to the center, hence we call this type of acceleration “centripetal” acceleration which means “center seeking”.

Circular MotionCircular Motion

• Solving circular motion problems is like a typical “force” problem where the motion is circular rather than linear.

• F = ma still works, now we have a new term for centripetal acceleration

• ac = v2/r acceleration (centripetal) = velocity squared/radius.