1. Circular Motion
Physics

2. Imagine a hammer (athletics variety) being spun in a horizontal circle
At a constant speed

3. Parts of a circle R = the radius of the circle
The circumfrence is found by using the formula 2pR or pD (D=the diameter of the circle)
The area is found by using the formula pR2
p = 3.14 R

4. Examples of Circular motion
Hard Drive
CD Player
DVD
Record player
Merry go round
Sling-shot
Bucket on a rope
Orbiting planet
Swinging Christmas tree lights

5. Different Tangential Speeds
Circular Motion
Rotational Speed: Revolutions per second
Tangential Speed: Total distance per second
Same Rotational Speed
Different Tangential Speeds

6. Important facts:
An object traveling in a circle has linear, and rotational speed.
Linear speed is measured in m/s
Rotational speed is measured in cycles per second. (frequency)
Linear Speed

7. Important Facts:
Even if the object is moving at constant speed, the object is accelerating, because it is changing direction.
The direction that the objects changes to is always towards the center of the circular path.

8. Why does it accelerate Inward?
In order for an object to accelerate their must be a net force acting on the object (Newton’s second law)
The force must be pointing towards the center of the circle.
                     
The force to the left is holding the rock inward…
It is coming from the string.

9. Other Examples
The picture to the right is of a car traveling around a corner.
The centripetal force is coming from friction
The next picture is the moon traveling around the earth.
The force is coming form the gravity of the earth.
                
              

10. Question:
What would be the force called on a loop the loop on a roller coaster?
Label the forces at the bottom sides, and top of the loop.

11. What is happen when your car make right turn?
For an object to stay in circular motion, there must be a force constantly pulling it towards the center of the circular motion.

12. How do we calculate the motion?
Acceleration:
ac = v2 r
Force
Fc = mv2

13. Symbols v = tangential (linear) speed of the object
ac = centripetal acceleration
Fc = centripetal force
r = the radius
m = mass
T = period (time to complete one circle)

14. Which car is easier to turn. Big mass or small mass
Which car is easier to turn? Big mass or small mass? Fast car or slow car?
Centripetal force is required amount of force pulling towards the center of the circle for the object to stay in circular motion.

15. Velocity T = period time for 1 rotation Also
Frequency rotations per sec

16. Centripetal vs. Centrifugal
The centripetal force is the force that causes an object to travel in a circle.
The centrifugal force is the inertia of the object that makes it want to continue in a straight line.
There really is no such thing as centrifugal force… it is only inertia.

17. Examples
A 150 g ball is tied to a string. If a student swings the ball so that it has a radius of .600 m, and a frequency of 2 rev/s, (a) what is the centripetal acceleration, and (b) what is the centripetal force?
Draw a diagram first to find the speed.

18. Examples
The earth revolves around the sun once a year. If the radius is x 106 km, what is the acceleration that the earth encounters?