lecture chapter 5 part1

Lecture chapter 5 - Newtons laws r(How to find a from given forces Newton#1 If the net force on an object is r r zero v is constant(stay rest or

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Newton’s laws: (How to find , from given forces?) Newton #1. If the net force on an object is zero, is constant. (stay rest or keep ) INERTIA (safety belt) Objects want to keep doing what they are already doing For example: in space …. (Attention: If friction, Air resistance… net force 0) Normal force N and gravity mg 2 forces on 1 object N and mg are 2 balanced forces. a r v r v r Newton #2 If net force 0 . is not constant, a 0 object’s acceleration will be in the same directions as the net force. v r a m F net r r =
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SI Unit for forces : Newton (N) F= m a 1 Newton force (net force), will give 1 kg object 1 m/s 2 acceleration. 1 N = 1 kg. 1 m/s 2 1 N = 1 kg.m/s 2 Example : gravity, ( free fall, jump, projectile, same acceleration g. downward) G= mg weight = mass . g g= 9.81 m/s 2 Also g = 9.81 N/kg = 9.81 N/kg =9.81 kg . m/s 2 kg 1 kg object’s weight on earth is 9.81 N 100gram (about 3 oz) object weights about 1 N. Attention: when you solve problem, if you first convert every value to standard SI unit. (m, s, m/s, m/s 2 , N, ….) you can plug the numbers and automatically get SI unit in your answer.
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Strategy: Always convert to SI unit before using equations. Example: = = = minutes 1 . 0 / 24
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This note was uploaded on 08/25/2010 for the course PHYS 111 taught by Professor Jamesm.lockhart during the Spring '09 term at S.F. State.

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Lecture chapter 5 - Newtons laws r(How to find a from given forces Newton#1 If the net force on an object is r r zero v is constant(stay rest or

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