# Lect_08 - What is a force It's a pull or a push F F Lecture...

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Lecture 8 Forces: Newton’s First and Second What is a force? It’s a pull or a push. It has a magnitude and a direction F G G Forces are vectors! Types of forces Types of forces 1. Contact forces: -Grav itat iona l -E lectr ic±and ±Magnet ic -Weak force (important in subatomic world) -Strong±force (important in subatomic world) -Norma l force (always perpendicular to contact surface); it’s the basic “push” -Tens ion (force through a string, cable, rope, etc): it’s the basic “pull” -Fr ict (appears when two surfaces slide or try to slide one against the other) 2. Action at distance or non-contact forces : (The fundamental forces of Nature!) Newton Newton ’s Three Laws s Three Laws 1. Any object remains at rest or in motion along a straight line with constant speed unless acted upon by a net force. 3. Forces occur in pairs: For every force (or action) there is an equal but opposite force (or reaction) on B by A on A by B FF =− GG 2. net all m a == G G G

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Newton ’s First Law s First Law Any object remains at rest or in motion along a straight line with constant speed unless acted upon by a net force DEMO: Air table This law tells you what happens in the absence of any force, for instance in outer space ACT: Snapped string ACT: Snapped string A small ball attached to the end of a string moves in horizontal circles on a frictionless table as shown below. If the string snaps, what will be the trajectory of the ball?
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## This note was uploaded on 04/16/2008 for the course PHYSICS 221 taught by Professor Johnson during the Fall '06 term at Iowa State.

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Lect_08 - What is a force It's a pull or a push F F Lecture...

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