ApplyingNewtonsLaws-post

ApplyingNewtonsLaws-post - Suggested procedure for problem...

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PHY211 Applying Newton’s Laws 1 Suggested procedure for problem solving using Newton’s laws 1. Identify moveable parts of the system: Usually need to treat them separately 1 1 2 1 2 1 2 1 2 3 4
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PHY211 Applying Newton’s Laws 2 2. Draw all forces on each moveable part: Weight (W=mg) Normal, Tension, static friction (unknown) > If maximal static friction: f s = μ s N Kinetic friction (f k = μ k N) Any additional forces (e.g. push by hand) Make sure Newton’s 3 rd law is satisfied N 1 N 2 v f 1 f 1 = m 1 N 1 f 2 f 2 = m 2 N 2 W 1 W 2 N 1 N 2 F h v=0 f 2 Must know direction of velocity for direction of kinetic friction. Wrong direction of frictional force will produce wrong results. In case of static friction, must guess in which direction parts would move. Wrong guess does not lead to errors, but derived magnitude of frictional forces will be negative. W 1 W 1 =m 1 g W 2 W 2 2 g N v f= m N f W W=m g f 1 f i = m i N i usually not useful ! N 1 f 1 N 3 N 3
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PHY211 Applying Newton’s Laws 3 W 1 W 2 N T T For massless strings, tension forces on each end of the string are the same T 1 T 1 T 1 T 1 W 1 W 2 W 3 W 4 T 2 T 2 Each piece of String has its own Tension ( T 1 ,T 2 )
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ApplyingNewtonsLaws-post - Suggested procedure for problem...

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