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Sub unit 6.1 ”Power in Mechanical Systems”

Sub unit 6.1 ”Power in Mechanical Systems”. Introduction using @ a 10 Minute video Video shoes real life scenarios, equations, terms, and labels for both SI and English units.

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Sub unit 6.1 ”Power in Mechanical Systems”

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  1. Sub unit 6.1”Power in Mechanical Systems” • Introduction using @ a 10 Minute video • Video shoes real life scenarios, equations, terms, and labels for both SI and English units. • After video we have the following power point lecture that discusses terms and their interpretations, formulas and their labels, and we finish with sample problems to identify the students abilities to use the new information.

  2. Subunit 1Power in Mechanical Systems • Power: Rate of doing work • Power rating: maximum rate at which each machine can do work • www.teachertube.com/view_video.php?viewkey=b9e96fefd21d68ab729c

  3. Linear Mechanical Systems Force applied to object Distance object moves along the direction of the force acting on it Work = x W = f x d Work done by applied force Time to do the work Power = W t P = P = f x d t f x d t P = P = f x V Power = force x speed

  4. Rotational Mechanical Systems Torque applied Angle moved through x Work = W = T x θ T x θ t P = Since ω = θ/t W t P = P = T x ω Power = torque x angular speed

  5. SI Units for Mechanical Power 1 horsepower = 746 watts 1 horsepower = 550 English ft•lbs sec ft•lbs sec Joule sec N•m sec watt horsepower

  6. Efficiency • Efficiency: ratio of work out to work in or ratio of power out (Pout) to power in (Pin) Work In time Power In = Work Out time Power Out = Work Out Work In Power Out Power In % efficiency = % efficiency = X 100 X 100 Or…

  7. Sample Problem • Given: A steel casting weighs 200 pounds. It is raised 3 ft in 4 sec at a constant speed. • Find : horsepower of cylinder used to lift the steel casting. • 1st … • 2nd … 200 lb x 3 ft 4 sec 150 ft•lb/sec P = = 150 ft•lb/sec f x d t P = = 3 ft 4 sec P = f x V V = d/t = .75 ft/sec P = (200 lbs) (.75 ft/sec) =

  8. Sample Problem • Given: A crate weighs 980N and is lifted 2 meters in 2 sec. The winch pulls the cable a dist. Of 8 meters with a force of 272N in the same 2 sec. • Find : • A.) Input power (in watts) supplied to block and tackle by the winch • B.) Output power (in watts) of block and tackle used in lifting crate • C.) Efficiency of block and tackle

  9. Sample Problem Cont. (272 N) (8m) 2 sec = 1088 watts • A. • B. • C. Fin x Din Time N•m sec Pin = = 1088 = 980 watts Fout x Dout Time (980 N) (2m) 2sec N•m sec Pout = = = 980 = 90% Pout Pin 980 watts 1088 watts Efficiency = X 100 = = .90 x 100 =

  10. Sample Problem • Given: An electric motor has a shaft torque of .73 lb•ft when rotating at 1800 rpm. • Find : horsepower of the shaft P = T x ω ω = ( rev min ) ( 1 min 60 sec ) 6.28 rad. rev ( ) = 1800 188.4 rad/sec ft•lb sec P = .73 lb•ft x 188.4 rad/sec = 137.5 1 hp . 550 ft•lb sec ft•lb sec = .25 hp P = 137.5 x

  11. Sample Problem • Given: a piston in a compressor has a flywheel with a rate of 1100 rpm (115rad/sec) Torque is 65 N•m • Find : hp of flywheel P = T x ω 65 N•m x 115 rad/sec = 7475 watts ουσ ( )( ) 10.0 hp 1hp 746 watts = 7475 watts

  12. Lab Demos

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