Force and Motion: Stop Faking It!

Circular Motion!
A centripetal force pushes the object moving in circular motion towards the center of the circle. The second of two Web Seminars on the topic of Force and Motion was held on Thursday, January 25, 2007, from 6:30 p.m. to 8:00 p.m. Eastern time. The presenter was Dr. Bill Robertson, author of the popular NSTA Press series of books: Stop Faking It! The presentation focused on the topic of circular motion, a topic discussed on Dr. Robertson's book: Force and Motion: Stop Faking It!

Fifty-six (56) participants were present in addition to the presenter and the NSTA staff. Participating educators represented the states of Arkansas, California, Florida, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, New Hampshire, New York, North Caroline, Ohio, Oklahoma, Pennsylvania, Puerto Rico, South Carolina, Tennessee, Texas, Washington, Wisconsin, and Wyoming. Some of the participants had attended one of the two symposia on the same topic at the Area Conferences in Omaha and Baltimore.

In this presentation educators had the opportunity to learn about circular motion. Dr. Robertson explained that for an object to move on a circular motion at constant speed, a force that acts toward the center of the circle must exist. That force is called centripetal force. This force is the name given to all the forces that are already present, that happen to cause the object to move in a circle. Dr. Robertson also defined the term centrifugal force as the force that pushes the object away from the center of the circle in which it is moving. To understand the idea of the centrifugal force, Dr. Robertson described the concept of "frame of reference". Only when you view things from a rotating frame of reference, a centrifugal force appears. This force is very real to someone in that frame of reference. The centrifugal A centrifugal force is only real to an observer in the rotating frame reference. force does not exist if you are not in a rotating frame of reference.

Dr. Robertson used diagrams from his book Force and Motion: Stop Faking It! Finally Understanding Science So You Can Teach It to explain the concepts of centripetal and centrifugal forces. He asked many questions to engage the audience and assess their knowledge level. All participants received a copy of NSTA's SciGuide on Force and Motion.

Here are some comments provided by the participants at the end of the Web Seminar:

  • "This was a very informative session. I took physics in college but never really 'got it' and feel very uncomfortable teaching it."
  • "I will be teaching science for the first time this fall, this was a useful refresher."
  • "I start a unit on Force and Motion next week. I do not feel confident usually. After tonight's discussion, I feel much more comfortable with circular motion."
  • "Teaching physical science without a degree in it sometimes makes me inadequate at doing it. Any education I receive only allows me to be better at educating my students."

Thanks to the participants and the presenter for the learning opportunity, the interactions, and a job well done!

Web Seminar II Resources


See a recorded version of the Web Seminar.

PowerPoint Presentation

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Underwritten in part by NSTA Press