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## Work, Power, and Machines

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**Work**• A quantity that measures the effects of a force acting over a distance • Work = force x distance • W = Fd**Work**• Work is measured in: • Nm • Joules (J)**Work Example**• A crane uses an average force of 5200 N to lift a girder 25 m. How much work does the crane do?**Work Example**• Work = Fd • Work = (5200 N)(25m) • Work = 130000 N m = 130000 J**Power**• A quantity that measures the rate at which work is done • Power = work/time • P = W/t**Power**• Watts (W) is the SI unit for power • 1 W = 1 J/s**Power Example**• While rowing in a race, John uses 19.8 N to travel 200.0 meters in 60.0 s. What is his power output in Watts?**Power Example**• Work = Fd • Work = 19.8 N x 200.0 m= 3960 J • Power = W/t • Power = 3960 J/60.0 s • Power = 66.0 W**Machines**• Help us do work by redistributing the force that we put into them • They do not change the amount of work**Machines**• Change the direction of an input force (ex car jack)**Machines**• Increase an output force by changing the distance over which the force is applied (ex ramp) • Multiplying forces**Mechanical Advantage**• A quantity that measures how much a machine multiples force or distance.**Mechanical Advantage**Inputdistance Mech. Adv = Output Distance Output Force Mech. Adv. = Input Force**Mech. Adv. example**• Calculate the mechanical advantage of a ramp that is 6.0 m long and 1.5 m high.**Mech. Adv. Example**• Input = 6.0 m • Output = 1.5 m • Mech. Adv.=6.0m/1.5m • Mech. Adv. = 4.0**Simple Machines**9.2**Simple Machines**• Most basic machines • Made up of two families • Levers • Inclined planes**The Lever Family**• All levers have a rigid arm that turns around a point called the fulcrum.**The Lever Family**• Levers are divided into three classes • Classes depend on the location of the fulcrum and the input/output forces.**First Class Levers**• Have fulcrum in middle of arm. • The input/output forces act on opposite ends • Ex. Hammer, Pliers**First Class Levers**Input Force Output Force Fulcrum**Second Class Levers**• Fulcrum is at one end. • Input force is applied to the other end. • Ex. Wheel barrow, hinged doors, nutcracker**Second Class Levers**Output Force Fulcrum Input Force**Third Class Levers**• Multiply distance rather than force. • Ex. Human forearm**Third Class Levers**• The muscle contracts a short distance to move the hand a large distance**Third Class Levers**Output distance Input Force Fulcrum**Pulleys**• Act like a modified member of the first-class lever family • Used to lift objects**Pulleys**Output Force Input force**The Inclined Plane**• Incline planes multiply and redirect force by changing the distance • Ex loading ramp**The Inclined Plane**• Turns a small input force into a large output force by spreading the work out over a large distance**A Wedge**• Functions like two inclined planes back to back**A Wedge**• Turns a single downward force into two forces directed out to the sides • Ex. An axe , nail**Or Wedge Antilles**from Star Wars**Not to be mistaken**with a wedgIEEEEE**A Screw**• Inclined plane wrapped around a cylinder**A Screw**• Tightening a screw requires less input force over a greater distance • Ex. Jar lids**Compound Machines**• A machine that combines two or more simple machines • Ex. Scissors, bike gears, car jacks