Introduction
An object undergoes Uniform Circular Motion (UCM) when it moves around a circle of constant radius at a constant speed. When an object undergoes UCM its x and y components of position and velocity are always changing. This makes them more difficult to deal with than, if instead, we choose the direction pointing towards the center of the circle. The radial direction, and the direction that points around the circle, called the tangential direction, provide a simplification in the analysis. Objects undergoing UCM have a net force pointing towards the center of the circle - entirely in the radial direction. The acceleration is also thus in the radial direction, according to Newton's 2nd Law, and is equal to ar = v2/r, where v is the speed and r is the radius.
Uniform Circular Motion and Acceleration
Key Terms
Much of the key terms for UCM similar to what we've already introduced but with a few new specialized terms. Review them and make note of any unfamiliar definitions to you;
Text/Videos
Radial Acceleration (Centripetal) chapter:
and Net Radial Force (Centripetal) chapter:
Warning: careful consideration must be made when using the term centripetal force, as it implies an actual force, separate from others, in the radial direction. The term centripetal is referring to the net effect of all the real forces when an object is in UCM. In the case of UCM the net force is in the radial direction and that net force (from real forces) is called the centripetal force. Often students will describe a centripetal force as a source rather than a description of the phenomena, to avoid this make sure to describe what type of force is causing the centripetal force i.e. a normal force on a roller coaster, a friction force between a car and a race track etc.
Secondarily the Circular Motion page by Physclips, an Australia physics education project has excellent clips with animation that describe most of UCM including the directions of some very important vectors. Make sure to watch the Uniform Circular Motion clip and the Centripetal Acceleration clip under Circular Motion in the module. Don't forget to take notes! *Aside: remember that a differential or dv implies a very small change in velocity in this case and the a is just the average acceleration, which is still a vector.
Finally, the Physics Classroom UCM page offers a concise short description worth reading in addition to the textbook above.
Simulations
The Return of the Ladybug Revolution: part II
Additional Studying/Review
The following are great sources of additional information and insights into UCM. Referring to these when studying or doing homework is highly recommended.
- Another great video for studying with an enthusiastic teacher; Chris Doner UCM.
- For review and to test you basic knowledge feel free to visit EasyPhysic Circular Motion page.
- Finally, here is another section from chapter 6 of the OpenStax textbook on Fictitious Forces and Non-Intertial Frames as well as the Coriolis Effect.
- Recall the Frames of Reference [1960] film that was introduced on the Newton's First Law section, this will help you understand fictitious forces much better.
Extras
A cool lecture slide that may have some useful bits for review and notes; Lehman College Physics slides.