CHAPTER 5 WORK AND MACHINES

PS 10 c,d I can solve problems to calculate work and power. W=F x d P= W/tI can solve problems to calculate work and power. W=F x d P= W/t I can apply the concept of mechanical advantage to explain how machines make work easier.I can apply the concept of mechanical advantage to explain how machines make work easier. I can explain how work, force, and motion apply to machines.I can explain how work, force, and motion apply to machines. I will be able to list the six simple machines and give examples of each.I will be able to list the six simple machines and give examples of each. I will be able to recognize a compound machine and tell which simple machines it makes up.I will be able to recognize a compound machine and tell which simple machines it makes up.

SECTION 1 WORK WORK The transfer of energy that occurs when a force makes an object moveThe transfer of energy that occurs when a force makes an object move For work to occur, the object must move and the movement must be in the same direction as the applied forceFor work to occur, the object must move and the movement must be in the same direction as the applied force work = force x distancework = force x distance w = F x d w = F x d work measured in Joules (J) work measured in Joules (J) force measured in Newtons (N) force measured in Newtons (N) distance measured in meters (m) distance measured in meters (m)

POWER Amount of work done in a certain amount of time.Amount of work done in a certain amount of time. Power = work/timePower = work/time P = W/t P = W/t Power is measured in watts (W)Power is measured in watts (W)

SECTION 2 USING MACHINES Machine: a device that makes doing work easierMachine: a device that makes doing work easier Machines make work easier by:Machines make work easier by: –increasing the force that is applied to an object; Ex. bottle opener, car jack –increasing the distance over which a force can be applied; Ex. leaf rake, ramp –changing the direction of the applied force; Ex. pulling on a blinds cord, ax

Effort force: force applied to the machineEffort force: force applied to the machine Resistance force: force applied by the machineResistance force: force applied by the machine Input work: work put into the machineInput work: work put into the machine Output work: work put out by the machineOutput work: work put out by the machine Some energy transferred is changed to heat due to frictionSome energy transferred is changed to heat due to friction Ideal machine: input work = output work because there would be no frictionIdeal machine: input work = output work because there would be no friction Mechanical advantage (MA): the number of times a machine makes the work easierMechanical advantage (MA): the number of times a machine makes the work easier –MA = Output force/input force –MA = slope/height

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EFFICIENCY measure of how efficient a machine ismeasure of how efficient a machine is Efficiency = output work/input workEfficiency = output work/input work always less than 100% always less than 100% A more efficient machine loses less energyA more efficient machine loses less energy

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SECTION 3 SIMPLE MACHINES LEVER:LEVER: –First class lever: crowbar, teeter-totter –Second class: wheelbarrow, bottle opener, door –Third class: rake, baseball bat, fishing pole

WHEEL AND AXLEWHEEL AND AXLE –Steering wheel, door knob, Ferris wheel, faucet handle

PULLEYPULLEY –Window blind, flag pole

INCLINED PLANEINCLINED PLANE –Ramp, stairs

WEDGEWEDGE –Knife, axe, zipper

SCREWSCREW –Jar lid, spiral staircase

COMPOUND MACHINES Two or more simple machines put togetherTwo or more simple machines put together –Pencil sharpener, bicycle

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