Work Power Simple Compound Machines Mechanical Ideal Mechanical

Work & Power Simple & Compound Machines Mechanical & Ideal Mechanical Advantage Efficiency By: Deborah Wang modified by: S. Ingle

Work Concepts 4 Work (W) ~ product of the force exerted on an object and distance the object moves in the direction of the force. – W is transfer of energy by mechanical means. – W is done on an object only if it moves in the direction of the force. – Only the component of the force in the direction of the motion does work.

Work Formulas Work = Force x displacement F W = Fd d 1 joule (J) = 1 Newton * meter (N * m) if force is exerted at an angle to direction of motion, W = (Fcos )d or W = Fd cos F d

Power 4 Power (P) ~ rate at which work is done or rate at which energy is transferred. Measured in watts. – Watt (W) ~ one joule of energy transferred in one second. Power = Work / time 1 watt = 1 joule / second (J/s)

Simple Machines 4 Machine ~ makes work easier either by changing the magnitude or the direction of a force, but can not increase the amount of work done. 1. 2. 3. 4. 5. 6. lever ~ bottle opener, seesaw, crowbar pulley ~ rope on flagpole, block & tackle wheel-an-axle ~ wheel barrow, bike pedals inclined plane ~ wheelchair ramp wedge ~ knife, axe, chisel screw ~ bottle cap, nut, bolt

Mechanical Energy 4 Effort force (Fe) ~ force you exert on a machine. 4 Resistance force (Fr)force exerted by the machine. Win= Fede Work input Wout= Frdr Work output

Ideal Machines 4 Ideal machines exist only in a frictionless, air resistance-less world. 4 No energy or work is lost to the system through outside forces 4 For ideal machines: Work input = Work out put so: Fe de = Fr dr

Mechanical Advantage 4 Mechanical Advantage (MA) ~ ratio of resistance force to effort force. MA = Fr / Fe 4 Ideal Mechanical Advantage (IMA) ~ ratio of effort distance to resistance distance. IMA = de / dr

Efficiency 4 Efficiency ~ ratio of work output to work input expressed in percent. efficiency = (Wout / Win) * 100% or efficiency = (MA / IMA) * 100%

Compound Machines 4 Compound machine ~ consists of two or more simple machines linked so that the resistance force of one machine become the effort force of the second. – Ex. The pedal and gear of a bicycle. 4 To calculate the efficiency of a compound machine you simply multiply the efficiencies of the simple machines that make it together.