Simple MachinesSimple Machines

Machine vs. Simple Machine vs. Simple MachineMachineMachine: Any device that makes

work easierSimple Machine

◦A device that does work with only one movement.

◦There are four main simple machines

Advantages of Simple Advantages of Simple MachinesMachinesMakes work easier by changing

the force you exert in size, direction or both.

Help overcome gravity and friction

2 Kinds of Work2 Kinds of WorkWork done by the machine (Wout)

Work done on the machine (Win)

Wout is always smaller than Win due to friction

W= f X d (J)

Applying ForceApplying Force2 forces when a machine does

work:◦Effort Force (Fe): the force applied to

the machine◦Resistance Force (Fr): the force

applied by the machine

Mechanical AdvantageMechanical AdvantageThe number of times a machine

multiplies the effort force MA = resistance force = Fr

effort force Fe

The higher the MA the lower the effort put in

Inclined PlaneInclined PlaneFlat slanting surfaceConnects one level to another

Modified Inclined Planes: Modified Inclined Planes: ScrewScrew

Screw◦Inclined Plane wound around a rod

Modified Inclined Planes: Modified Inclined Planes: WedgeWedge

WedgeInclined plane that movesInclined Plane that cuts

Inclined Plane MA Inclined Plane MA FormulasFormulas

Ideal Mechanical Advantage

IMA= de (length of slope)

dr (height of slope)

D=distanceE= effortR=resistance

Actual Mechanical Advantage

AMA= Fr (mass)

Fe (effort)

F=forceE=effortR=resistance

LeverLever

Pivots around a fulcrum which can increase force or increase distance

Effort armResistance arm

Mechanical Advantage of Mechanical Advantage of LeversLeversIMA = length of effort arm =

Le length of resistance arm Lr

AMA= R E

Classes of LeversClasses of Levers

First Class (EFR)◦ Ex: seesaw

Second Class (FRE)◦ Ex: Wheelbarrow

Third Class (REF)◦ Tweezers

Effort Resistance

Fulcrum

PulleyPulleyRope passing over a

grooved wheelChanges direction of

force or amount of force

PulleyPulley

Can be movable or fixed

Block and Tackle: combinations of pulleys to gain a large MA

AMA= R (resistance E (effort)IMA= Number of supporting strings

Wheel and AxleWheel and Axle

Wheel rotating around an axle

Ex: Doorknobs, faucets, etc.

Mechanical AdvantageMechanical Advantage

MA FormulaMA Formula

AMA= R

E

R=ResistanceE=Effort

IMA= Rw Ra

R=Radiusw=wheela= axle