1. AP Rotation and Centripetal
Day 11 Quarter 3
AP Rotation and Centripetal

2. Do you remember?
Tangential vs. Rotational/Angular
Get a clicker

3. You will look over and answer the next 3 questions as best you can for point A.

4. 1. There is a centripetal acceleration at the top and it is pointed: a. Down b. Up
2. The AMOUNT of centripetal force you get by making a free body diagram and finding the amount of imbalance to the center. At A it would be: a. mg because mg is down b. T + mg because both forces are down c. mg – T because mg is down and T is up

5. 3. If the string were to break at point A, at that moment the ball would go: a. Straight down because gravity is pulling it down at that point
b. At a downish angle because it is pulled down by gravity but going left
c. Straight left for that moment before it actually moves from gravity.

6. So Far Circular things:
Period T is time for one rotation, so 𝑉 𝑡 = 2𝜋𝑟 𝑇 where r is radius of curvature
The amount of inward imbalance Σ 𝐹 𝑐 =𝑚 𝑎 𝑐 where 𝑎 𝑐 = 𝑉 𝑡 2 𝑟

7. When something is circular
Know: It is going to deal with centripetal acceleration AND OR period.
Figure out what is being asked and which one it relates to (or both)
A quick sketch is VITAL

8. I have a mass of planet and a height above surface
I have a mass of planet and a height above surface. I am trying to find the speed Vt.
This involves the ACCELERATION probably because it involves mass and not any kind of time

9. ACCELERATION involves FORCES involves IMBALANCES

10. Try the next 3 questions for me, then we will vote on them.

12. E! I is true from our ideas II is true because the variables fit the ideas here (although technically its r + the inside radii) III is true b/c in this case, farther would mean there would be less velocity

17. Green Disk….get it out, remember
Try the next 2 questions

18. 9. GREEN DISK: What force kept the washers in place on the rough parts by resisting their desire to go forward?
A. Gravitation
B. Weight
C. Normal Force
D. Friction
E. Tension
F. Applied Force

19. 10. GREEN DISK: As you spin faster, does the force required to keep it curve go up/down? How can you tell?
Not voting just trying to answer

20. Lets see it in action
Describe it…

21. Lets see it in action
“As they went in a circle, their arms supplied the force to keep them circling. At the fast speeds, their arms could not supply the force needed at that radius to keep them curved, so they flew off in a tangent line”
Evaluate it, what is right/wrong here?

22. Lets see it in action
“The idiot experienced more outward force than they could pull and flew out”
Evaluate it, what is right/wrong here?

25. GEOSTATIONARY It rotates the same rate as Earth
So it is above the same point throughout its rotation.
Has to have the same period as Earth

26. FOR A
Probe A: It has the same period but is further, so covers more distance in that time
Probe B: It has a larger gravitational force and thus a larger acceleration

27. What it means for you
They have the SAME period as the planet, but since they are farther….they are traveling FASTER than the planet.
Incorrect thought: I am on Earth, and it is rotating. So my centripetal acceleration is In actuality, with math, its The acceleration due to rotation is small

28. FOR B
Probe A: Its faster but has more radius, and V is more important than r
Probe B: Its slower but has less radius, and r is more important than V

30. What it means for you For things ORBITING with periods…
𝑎 𝑐 = 4 𝜋 2 𝑟 𝑇
For a given period, more radius = faster

34. Do we include a centripetal force in our FBD?
No: A centripetal force does not exist on the mass as a force
Yes: In order to go in a circle, a centripetal force exists

35. Now create net force equations