Laws of Mechanics_units_memo_S_2012

Laws of Mechanics_units_memo_S_2012 - ME 3504/3514...

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C:\My Docs\3504\ME3504_S_2012\Syllabus\Handouts 2012\Laws of Mechanics_units_memo_S_2012.doc Page 1 of 6 ME 3504/3514 Vibrations / Systems Dynamic R. G. Kirk 8-26-99/ S 2012 Laws of Mechanics 1. Newton's 1 st Law : Definition of Momentum, v m . A body at rest or in motion will remain at rest or in motion unless acted upon by some external force. 2. Newton's 2 nd Law : Definition of force (or torque). The sum of all external forces acting on a body equals the body's time rate of change of momentum.  J dt d J J dt d T dt v m d F torsion for ; ) ( If mass is constant with time a m dt v d m F 3. Newton's 3 rd Law : For every action, there is an equal and opposite reaction. (Use this to build up system components into system equations of motion.) 4. Newton's 4 th Law : Mass attracts mass. Definition of weight. 2 R m m W b a Weight of body for engineering calculation taken as mg g W mg W c 1 or
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C:\My Docs\3504\ME3504_S_2012\Syllabus\Handouts 2012\Laws of Mechanics_units_memo_S_2012.doc Page 2 of 6 Systems of Units English Gravitational 2 f 2 f sec lb ft slug ft/sec slug lb 1 1 1 1 c g Acceleration of gravity = 32.17 ft/s 2 A slug is (lb m /32.17) and units are in feet only. English Engineering 2 f m c 2 m f 2 f m 2 m f sec lb ft lb 17 . 32 g ; ft/sec 17 . 32 lb 1 lb 1 s lb in lb 386 ; in/s 386 lb 1 lb 1 c c c g g g METRIC UNITS CGS MKS Distance centimeters (cm) meter (m) = 100 cm Mass grams (g) kilogram (kg) = 10 3 g Time seconds (s) seconds (s) Force 1 dyn = 1 g 1 cm/s 2 newton (N) = 10 5 dyn 1 N = 1 kg 1 m/s 2 Acceleration of gravity 980.6 cm/s 2 9.806 m/s 2 In English Engineering – acceleration of gravity, g is taken as 32.17 ft/sec 2 or 386 in/sec
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This note was uploaded on 01/23/2012 for the course ME 3504 taught by Professor Tschang during the Fall '08 term at Virginia Tech.

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Laws of Mechanics_units_memo_S_2012 - ME 3504/3514...

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