# 01-28-20 Notes ```LCPA ▪ PHYSICS (MS.APPEL)
5-1 NOTES: CIRCULAR MOTION
Name:
Page 1 of 2
Date: 10-30-17
Period:
Circular Motion
Notes
Linear vs. Circular Motion
Quantity
Linear Motion
Speed + Direction
Direction of the object’s motion
Circular Motion
Speed stays the same
Direction is tangent to the circle
𝐶ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦
Speed does not change;
Direction changes
Direction—Toward the center of the
circle
Velocity
𝑡𝑖𝑚𝑒
Acceleration
Force
Due to a push/pull
Direction of the push/pull
Push or pull
𝐹 = 𝑚∗𝑎
In the direction of the acceleration
Looking at Circular Motion
Centripetal force – “center seeking”
Centrifugal force – “center fleeing”  Fictitious! (Fake!)
Direction is toward the center of
circle
LCPA ▪ PHYSICS (MS.APPEL)
5-1 NOTES: CIRCULAR MOTION
Name:
Page 2 of 2
Date: 10-30-17
Period:
Circular Motion Problems
Important Quantities

Frequency (f):
𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦 =
Example:
5 revolutions in 40 seconds.
𝑓=

𝑁𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑟𝑒𝑣𝑜𝑙𝑢𝑡𝑖𝑜𝑛𝑠
𝑟𝑒𝑣
→ [
]
𝑡𝑖𝑚𝑒
𝑠𝑒𝑐
Velocity (v): 𝑣 =
𝑑𝑖𝑠𝑡𝑎𝑛𝑐𝑒
𝑡𝑖𝑚𝑒
→ [
𝑚
𝑠𝑒𝑐
5 𝑟𝑒𝑣
𝑟𝑒𝑣
= 0.125
40 sec
𝑠𝑒𝑐
]
𝑣 = 2𝜋𝑟𝑓

Centripetal Acceleration (ac):
𝑎𝑐 =

𝑣2
𝑟
Centripetal Force (Fc):
𝑚𝑣 2
𝐹𝑐 = 𝑚𝑎 =
→ [𝑁]
𝑟
Example: Captain Chip, the pilot of a 60,500 kg jet plane, is told that he must remain in a holding pattern
over the airport until it is his turn to land. If Captain Chip flies his plane in a circle whose radius is 50 km once
every 30 min, what centripetal force must the air exert against the wings to keep the plane moving in a
circle?
m = 60,500 kg
# rev = 1
Time = 30 minutes = 180 seconds
f =?
v=?
r = 50 km = 50,000 m
Fc= ?
1 𝑟𝑒𝑣
𝑟𝑒𝑣
= 0.0006
180 𝑠𝑒𝑐
𝑠
𝑟𝑒𝑣
𝑚
𝑣 = 2𝜋(50,000 𝑚) (0.0006
) = 175
𝑠
𝑠
𝑓=
𝑚 2
(175 𝑠 )
𝐹𝑐 = 𝑚 ∗ 𝑎 = (60,500 𝑘𝑔) (
) = 36, 900 𝑁
50,000 𝑚
```