1. CONCEPTUAL PHYSICS
Circular Motion

2. Rotations and Revolutions
Axis: straight line about which rotation takes place.
If axis is located within the body, the motion is called a rotation. Ex. Earth rotates and we have days
If object turns about an external axis, the rotational motion is called a revolution. Ex. Earth revolves around the sun.
Rotational speed
Linear speed: is greater on the outside of a rotating object than closer to its axis.
Linear speed of something moving
in a circle is tangential speed.
Rotational speed: refers to the
number of rotations or revolutions
per unit of time.

3. Expressed in revolutions per minute (RPM)
Linear speed increases as rotational speed increases and depends on the distance from the center.
All parts for example in a merry go round have the same rotational speed but different linear speed.
Centripetal force: any force that causes and object to follow a circular path.
Without this force, the occupants inside a rotating carnival ride would have a straight line motion.

4. Centrifugal forces Simulated gravity
Centrifugal force: a force “away from the center”
It is useful only in a rotating frame of reference.
The only force that keeps an object moving in a circular path is the centripetal force.
In a rotating frame of reference, centrifugal force appears as real as the pull of gravity. But is not a true force because it is an effect of rotation and not the interaction between two masses.
Simulated gravity
Gravity is simulated by centrifugal force.
YouTube - conceptual physics Centripital force

5. In the future, we will likely life in huge lazily rotating space stations where centrifugal forces simulate gravity.
Right now, astronauts feel weightless because they lack a support force.
To simulate normal Earth gravity at 1 RPM require a structure almost 2km in diameter and people have difficulty adjusting to RPM greater than 2 or 3 RPMs.

6. Formulas
Period(T): the time it takes for one full rotation or revolution of an object. (unit: second)
Frequency(f): the number of rotations or revolution per unit of time. Unit: 1/second or Hertz (Hz)
T= f= 1
f T
For an object that spins in a circle, the distance it travels in one revolution is 2r
Tangential velocity (v) v= 2r T
Centripetal acceleration :ac=v2/r
Centripetal force: Fc=mac=mv2 r

7. Ex. 1 If Karen spins on her chair with a frequency of 0
Ex.1 If Karen spins on her chair with a frequency of 0.5Hz, what is her period?
Ex.2 Silvia’s favorite ride at the fair is the rotor, which has a radius of 4.0m. The ride takes 2.0s to make one full revolution.
a. What is Silvia’s tangential velocity?
b. What is her centripetal acceleration?

8. Ex. 3 Captain Ramos, the pilot of a 60500kg plane, is told that he must remain over the airport until it is his turn to land. If Captain Ramos flies his plane in a circle whose radius is 50.0km once every 30.0min, what centripetal force must the air exert against the wings to keep the plane moving in a circle?

9. CONCEPTUAL PHYSICS
Circular Motion