Uniform Circular Motion

Definition: the motion of an object in a circular path with a constant speed

Homework: Read pages 153 – 156P 156 Answer questions:

12, 13, 14, 15

When does this happen?

• Driving a car at constant speed around a circular corner

OR

Speed in a circular path

Recall: to find speedV = distance / time

for a circular path d = 2 p rthe time required to complete one full revolution is called the period (T)

Therefore, v = 2pr / T

Constant speed, but what about velocity?

• Velocity of an object undergoing UCM is always directed tangent to the circular path

• Direction is constantly changing, velocity is not constant

• Therefore, the object must be accelerating

Centripetal Acceleration

• Acceleration experienced by an object moving in a circular path at a constant speed.

• Directed to the center of the circular path• centripetal means “center seeking”

ac = V2 / r

Centripetal Force

• Force directed toward the center of the circular path

• Causes the centripetal acceleration

Fc = m ac

Do Now

Assume that the moon orbits the Earth in a circular orbit in 27.32 days. Using the List of Physical Constants on your Reference Tables, calculate the following:

a. the speed of the moon in its orbit.b. the centripetal acceleration experienced by

the moonc. the centripetal force that keeps the moon in

its orbit.

The answers:

a. V = 1022 m/s

b. ac = 0.00272 m/s2

c. 2.0 x 1020 N