1. Factors Affecting Circular Motion
Centripetal Force
Factors Affecting Circular Motion

2. Recap

3. Curves, Centrifugal, Centripetal Forces
Going around a curve smushes you against window
Understand this as inertia:
your body wants to
keep going straight
but the car is accelerating
towards the center of the curve
The Car accelerates
 you think you’re being accelerated

4. Centripetal, Centrifugal Forces, continued
The car is accelerated toward the center of the curve by a centripetal (center seeking) force
The name for the “net force toward the center of the circle” that causes circular motion to occur
NOT a separate force. Can use Fnet to represent it.
In your reference frame of the car, you experience a “fake”, or fictitious centrifugal “force”
Not a real force, just inertia relative to car’s acceleration
Centripetal Force
on car
velocity of car
(and the way you’d rather go)

5. Centripetal Force
What provides it?

6. Car Around a Curve - Friction
If there isn’t enough friction (icy or wet road), the car doesn’t make the curve!

8. Mythbusters!

10. Where v is the angular (rotational) speed

13. Fnet

15. The forces real and perceived
Rotating Drum Ride
Vertical drum rotates, you’re pressed against wall
Friction force against wall matches gravity
Seem to stick to wall, feel very heavy
The forces real and perceived
Real Forces:
Friction; up
Centripetal; inwards
Gravity (weight); down
Perceived Forces:
Centrifugal; outwards
Gravity (weight); down
Perceived weight; down and out

17. Remember…
Fnet

18. A 1500-kg car goes around a curve with a radius of 50
A 1500-kg car goes around a curve with a radius of 50.0-m at a speed of 8.0 m/s.
a) How much Fc is needed?

19. A 50. 0-g cork on a 1. 00-m string twirls at 3. 00 rev/s
A 50.0-g cork on a 1.00-m string twirls at 3.00 rev/s. The string can hold only 20.0-N. Will it break?
IT WILL HOLD!!!