2What is a Machine? Machine: device that makes doing work easier. Knife ScissorDoorknobCar engine
3Making work easier Machines make work easier by: increasing the force that can be applied to an object.Car Jack allows you to lift carIncreasing the distance over which a force can be applied.RampsChanging the direction of an applied force.Pull down on cord for blindsAmount of work does not change
4Work done by MachinesCrowbar – when you do work on the machine (crowbar), it does work on the lid.2 Forces involved:Effort force: force applied to the machineResistance force: force applied by the machine2 types of Work:Input work: Work done by you on a machineOutput work: Work done by the machine
5Conserving EnergyWhen you do work on a machine, you transfer energy to the machine.The work you get out of a machine can never be more than what you put into the machine.Actually some energy is always lost to friction so W(out) is always less than W(in).
6Ideal Machines W(in) = W(out) Fe X de = Fr X dr Fe = Force effort (what you exert)Fr = Force resistance (what you are moving)De = Distance effortDr = Distance resistanceHammer example
7Mechanical AdvantageThe number of times a machine multiplies the effort force.MA = FrFe* When only the direction of force changes, the MA = 1
8EfficiencyA measure of how much of the work you put into a machine is changed to useful output work by the machine.Eff = Wout X100%WinEfficiency is always less than 100%**Increase efficiency by decreasing friction.