NSTA Web Seminar: Force and Motion: Stop Faking It! LIVE INTERACTIVE YOUR DESKTOP Thursday, December 11, 2008

Force and Motion Speed and velocity Inertia and acceleration Newton’s second law Mass and weight Speed and velocity Inertia and acceleration Newton’s second law Mass and weight

Speed and velocity

Which animal had the greatest average speed for the entire race? TortoiseHare

Which animal had the greatest instantaneous speed during the race? TortoiseHare

Definitions Average Instantaneous speed = speed calculated over an infinitesimally small time period

Which of the following is true? All the balls moved exactly alike. All the balls moved with the same speed. All the balls were the same color. They weren’t really balls, it’s a computer simulation.

Let’s Pause for Two Questions from the Audience

Inertia and Acceleration

Inertia = the tendency of an object to keep on doing whatever it is doing, whether in motion at a constant speed or at rest

Acceleration = any change in speed and/or direction

Let’s Pause for Two Questions from the Audience

Newton’s second law

Mass is a measure of inertia. It’s just a number used to compare inertias.

Newton’s second law ΣF = ma ΣF represents the net force acting on an object. m represents the mass of an object, which is a numerical measure of its inertia. a represents the acceleration of the object.

24 Let’s Pause for Two Questions from the Audience

25 Mass and Weight

Mass is: Something you go to if you are Catholic. The amount of “stuff” in an object. A measure of an object’s inertia. A force that resists motion.

Weight is: The gravitational force the Earth exerts on an object. The gravitational force any object exerts on another object. The same as mass, but with different units. A good song by The Band

Mass is a measure of inertia. It is the m that goes into F = ma. Weight is the force that gravity exerts on something. Weight is the F in F = ma.

The accelerations of the two objects are the same For the large object: F = ma Weight of large object = (mass of large object)(acceleration of large object) W = m g For the small object: F = ma Weight of small object = (mass of small object)(acceleration of small object) w = mg

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For an object near the surface of the Earth: F = ma

Thank you! Let’s Pause for Two Questions from the Audience

Thanks to our presenter, Dr. Bill Robertson, and to NSTA Press for sponsoring this program

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NASA: Discover the Universe – From Galileo to Today December 16, 2008 NSTA Press: Picture-Perfect Science Lessons December 17, 2008 FDA: Teach Science Concepts and Inquiry with Food December 18,

National Science Teachers Association Dr. Francis Q. Eberle, Executive Director Zipporah Miller, Associate Executive Director Conferences and Programs Al Byers, Assistant Executive Director e-Learning LIVE INTERACTIVE YOUR DESKTOP NSTA Web Seminars Flavio Mendez, Senior Director Jeff Layman, Technical Coordinator