This text is meant to accompany class discussions. It is not everything there is to know about uniform circular motion. It is meant as a  prep for class. More detailed notes and examples are given in the class notes, presentations, and demonstrations (click here.)

Click for the questions that go with this reading
Objectives
Students will be able to:

  • Define the period of motion
  • Define the frequency for motion
  • Mathematically relate the period and frequency
  • Convert from RPM’s (revolutions per second) to Hertz
  • Use the definitions of period and frequency to solve word problems
  • Discuss the relationship between centrifugal and centripetal forces.
  • Describe why a person slides to the outside of a curve in a car as observed from inside the car.
  • Discuss what supplies the centripetal forces
  • Correctly write the units equations from memory
  • List the S. I. units associates with each quantity
  • Solve word problems utilizing the formulae and concepts in the unit.
  • Calculate the g’s felt by a rider in an amusement park when
    • He/she is spun in a horizontal circle (e.g. carousel)
    • He/she is spun in a vertical circle (e.g. roller coaster loops, playground swings.)
  • Describe why an irregular shaped roller coaster loop is better than a circular loop.
  • Solve problems based on an automobiles ability to supply a lateral acceleration and “cornering.”
  • Solve problems utilizing formulae and ratio.

 
Introduction

     "Uniform circular motion" means that a body is turning or traveling at a constant speed. It is not speeding up or slowing down. See the animation below for a comparison of the the two types of circular motions.

Usually, when we think of a car accelerating, we think the car as traveling in a straight line and its speed is changing, i.e. speedng up or slowing down. The motions we have calculated has been one dimensional (along a line.) Up to now an acceleration has meant a change in the velocity's MAGNITUDE with no change in direction.

Notice how "at" is in the same direction as the velocity. This also shows that a force in the same direction as the velocity will change the body's speed and any direction change would occur along the same straight line. But what would happen if the force was NOT applied parallel to the direction of the motion?

A force that is not applied parallel to the velocity changes the body's direction. (As in the animation above.) It may or may not change the velocity's magnitude.

 
 

by Tony Wayne ...(If you are a teacher, please feel free to use these resources in your teaching.)