CH 14 Work, Power, and Machines 14.1 Work and Power Work (W) Product of force and distance Requires movement No movement = no work done Calculating Work W = F x d Work = Force x distance Unit: Joule (J) (N.m)

Power Calculating Power Rate at doing work Doing work at a faster rate needs more power Increase in power takes: Increase amount of work in time Do work in less time Calculating Power Power = work ÷ time SI unit: watt (W) is 1J/second 1 horsepower (hp) = 764W

14.2 Work and Machines Machines Devise that changes force Make work easier to do Change Size (jack for a car) Direction (oar of boat) Distance a force acts (size of oar)

Work input and work output Because of friction, work done by a machine is always less than work done on the machine Work input Input force: force you exert on machine Input distance: distance force acts on Work output: work done by input force Work output Output force: work done by the machine Output distance: distance force acts on Work output = output force x output distance

14.3 Mechanical Advantage and Efficiency Number of times machine increases input force Actual Mechanical Advantage (AMA) Ratio of output force to input force AMA = Output force ÷ Input force Ideal Mechanical Advantage (IMA) Mechanical advantage without friction IMA = Input distance ÷ output distance Friction always present to AMA > IMA

Efficiency Percentage of work input that work output Because of friction no machine is ever 100% efficient Efficiency = (work output ÷ work input) x 100%

14.4 Simple Machines Lever Wheel and Axel: Bar that moves on fixed point (fulcrum) IMA = input arm ÷ output arm First class lever: seesaw, scissors, screwdriver Second class lever: wheelbarrow Third class lever: broom Wheel and Axel: 2 disks with different radius IMA: radius (or diameter) input force ÷ radius (or diameter) output force exerted Ex: steering wheel, screwdriver

Inclined Plane Wedge Screw Slanted surface, to move objects to different elevations IMA= distance inclined plane ÷ change in height Wedge V-shaped object; 2 inclined planes Thin wedge has greater IMA than a thick wedge Screw Inclined plane wrapped around a cylinder Closer threads have greater IMA

Pulley Compound Machines IMA = number of rope sections supporting the load being lifted Fixed: wheel attached to fixed location, IMA= 1 Moveable: attached to load Pulley System: fixed and movable pulleys, large MA Compound Machines Combination of 2+ simple machines