1. What things move in a circular path?
amusement rides
planets & moons
car driving a curve (part of a circle)
lasso
merry-go-round
racetrack
jet fighter
wash machine
centrifuge

2. What are the two types of circular motion?

3. Rotation vs Revolution
Object turns about in ___________ axis
Rotation:
Object turns about an __________ axis

4. Circular Motion (Material from Ch 10 - 12)
How do Newton’s Laws apply to Circular Motion?

5. Newton’s First Law - Inertia
States that every object continues in a state of rest or uniform speed in a straight line unless acted upon by an net force….
Ex. Spinning bike tire will burn your hand if you try to stop it – heat/friction force

6. Newton’s 2nd Law Forcenet = mass x acceleration or
acceleration = Net Force/mass
The Force is perpendicular to the lever arm.

7. Newton’s 3rd Law of Motion
For every action there is an equal and opposite reaction.

8. You are on a merry-go-round rotating with a constant speed
You are on a merry-go-round rotating with a constant speed. Is there a net force acting on you?
Yes No

9. If a stopper is twirled on a string and the string suddenly breaks, the stopper will move in which direction? 4 3 1 2
Path 1
Path 2
Path 3
Path 4 52 of 61

10. Implications for Circular Motion
What does Newton’s 2nd Law imply about objects moving in a circle?
The state of motion is always changing so a net force MUST be acting.
The centripetal (center-seeking) force keeps the object from moving in a straight line.
The object accelerates away from its straight line path.

11. 10.3 Centripetal Force
The force exerted on a whirling can is _______________________________. No outward force acts on the can.

12. Centrifugal Force NO SUCH THING!!! Centrifugal means center-fleeing
Not a force but a feeling we get due to the inertia of our bodies wanting to continue in a straight line.
Don’t use the f-word!!!

13. Equations for Circular Motion
speed,
acceleration,
centripetal force,

14. Sample Problem: Curved/Circular Motion
A car is taking a 52 m radius curve at 21 m/s. The car’s mass is 1015 kg.
a) What is the acceleration of the car?
b) What amount of force is acting on a passenger whose mass is 58 kg?
c) What amount of force is acting on the car?

15. a) a = (21m/s)2/52m a = 8.5 m/s2 b) F = 58kg(8.5m/s2) F = 490 N
c) F = 1015kg(8.5m/s2) F = 8600 N v F a
r = 52 m, v = 21 m/s, mc = 1015 kg, mp = 58 kg

16. The astronauts move in a circular orbit around the earth
The astronauts move in a circular orbit around the earth. Why do they appear to be “weightless”?
A. There is no gravity in space and they do not weigh anything.
B. Space is a vacuum and there is no gravity in a vacuum.
C. Space is a vacuum and there is no air resistance in a vacuum.
D. None of the above

17. Astronauts and “Weightlessness”
Astronauts and Shuttle falling away from straight line path at same rate
There IS gravity acting on both of them! v v a F a F
Demo: bucket of water rotated overhead
To avoid confusion, NASA now uses the term microgravity instead of weightlessness

18. Rotor Ride Fc a v Ff Fc W Top View Side View
into video: pause to discuss why feel pushed against door when take curve. Fc W

19. 10.2 Rotational Speed
_____ parts of the turntable rotate at the same _____________ speed or ______s.
A point farther away from the center travels a ________ path in the ________ time and therefore has a ____________ tangential or linear speed.
A ladybug sitting twice as far from the center moves ___________ as fast.

20. 10.2 Rotational Speed think!
At an amusement park, you and a friend sit on a large rotating disk. You sit at the edge and have a rotational speed of 4 RPM and a linear speed of 6 m/s. Your friend sits halfway to the center. What is her rotational speed? What is her linear speed?