Force and Motion: Stop Faking It!

Gravity!
The first of two Web Seminars on the topic of Force and Motion was held on Tuesday, December 5, 2006, 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 gravity, a topic discussed on Dr. Robertson's book: Force and Motion: Stop Faking It!

Seventy-four (74) participants were present in addition to the presenter and the NSTA staff. Participating educators represented the states of Arkansas, California, Florida, Georgia, Idaho, Illinois, Iowa, Kansas, Kentucky, Louisiana, Maryland, Massachusetts, Michigan, Missouri, Nebraska, Nevada, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Puerto Rico, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Virginia, Washington, and Wisconsin. 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 the concept of gravity. Dr. Robertson first talked about the effects of gravity on objects falling close to the surface of the Earth. Robertson concluded that if you ignore air resistance, all objects dropped from the same height land at the same time regardless of their mass. Objects falling to the Earth have the same acceleration; this acceleration is called "g" and it is equal to 9.8 meters per second per second. The presenter then proceeded to define the term "weight." He described weight as the force of gravity exerted by the Earth on all objects.

Dr. Robertson also explained how the force of gravity affects objects far away from the surface of the Earth. He explained that a different mathematical expression must be used to calculate the force of gravity exerted by the Earth on objects away from the Earth's surface. To gain a better understanding of this concept, web seminar participants used a simulation to manipulate the distance a satellite is located from the Earth to determine its weight, i.e., the force of gravity exerted by the Earth on it. The results showed that as an object moves away from the Earth, the force of gravity exerted by the Earth on the object gets smaller. Dr. Robertson concluded the web seminar talking about objects in orbit around the Earth or free fall and the concept of weightlessness. 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:

• "It cleared up some misconceptions I had about acceleration and mass close to the Earth."
• "My children love to do science; they are in the 5th grade. I was a secondary science teacher before becoming a science teacher educator. I suspected that Bill would have a better way to explain the concept to my kids and I was correct. Excellent Job!"
• "I teach pre-service teachers who really struggle with force and motion concepts. Their intuitive ideas seem to block a more scientifically accurate explanation. This was very relevant to my class needs."
• "There is always a lot of confusion between mass, weight, and gravity. The graphics and question quizzes along the way helped a lot!"

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

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