http://www.ck12.org Chapter 5. Centripetal Forces
5.1 Circular Motion
- Describe the velocity, speed and acceleration in circular motion.
Students will learn that in circular motion there is always an acceleration (and hence a force) that points to the center
of the circle defined by the objects motion. This force changes the direction of the velocity vector of the object but
not the speed. Students will also learn how to calculate that speed using the period of motion and the length of its
path (circumference of the circle it traces out).
Key Equations
v=^2 Tπr
If a particle travels a distance 2πrin an amount of timeT, then its speed is distance over time or^2 Tπr
The Earth-Sun distance is about 1. 5 × 1011 mThe Earth-Moon distance is about 3. 84 × 108 m
Guidance- An orbital period,T, is the time it takes to make one complete rotation.
- If a particle travels a distance 2πrin an amount of timeT, then its speed is distance over time or 2πr/T.
- An object moving in a circle has an instantaneous velocity vectortangentialto the circle of its path. The force
and acceleration vectors point to the center of the circle. - Net force and accelerationalwayshave the same direction.
- Centripetal acceleration is just the acceleration provided by centripetal forces.