1. Circular Motion r v
Fc, ac

2. Centripetal acceleration – acceleration of an object in circular motion. It is directed toward the center of the circular path.
ac = centripetal acceleration, m/s2
v = tangential speed, m/s
r = radius, m

3. Centripetal Force – the net inward force that maintains the circular motion of an object. It is directed toward the center.
Fc = centripetal force, N
m = mass, kg
ac = centripetal acceleration,
m/s2
v = tangential speed, m/s
r = radius, m

4. For a constant tangential speed:
v = tangential speed, m/s
d = distance, m
t = time, s
r = radius, m
T = period, s (time for 1 rev.)
If rpm (revolutions per minute) is given, convert to m/s using these conversion factors: and 1 min. = 60 sec.
Or you can find the period by taking the inverse of the frequency.
T = period, s – time for one revolution
F = frequency, rev/s – number of revolutions per time
Note: Period and frequency are inverses.

5. Since centripetal force is a net force, there must be a force causing it. Some examples are
A car going around a curve on a flat road: Fc = Ff (friction force)
Orbital motion, such as a satellite: Fc = Fg (weight or force of gravity)
A person going around in a spinning circular room: Fc = FN (normal force)
A mass on a string (horizontal circle, i.e.. parallel to the ground): Fc = T (tension in the string)

6. For a mass on a string moving in a vertical circle, the centripetal force is due to different forces in different locations.
At the top of the circle, Fc = T + Fg (tension plus weight or gravity)
At the bottom of the circle, Fc = T - Fg (tension minus weight or gravity)
On the outermost side, Fc = T
Anywhere other than above, you would need to find the component of gravity parallel to the tension and either add or subtract from tension depending on the location on the circular path