Physics! Simple Machines!

What is work? When you exert a force on an object that causes it to move some distance Work=Force x Distance

Mechanical Advantage mechanical advantage (MA) is the factor by which a mechanism multiplies the force or torque applied to it.force torque

Calculating Mechanical Advantage MA = distance over which force is applied/ distance over which load is moved MA = output force/input force

Inclined Plane A flat sloped surface How it works: exert a force over a longer distance Mechanical Advantage: divide length of incline by its height ▫I MA = LI/HI 3 1

Inclined Plane When is this an advantage? ▫Using a ramp versus lifting straight up ▫Begin the motion of an object Input force Output force

Wedge Thick at one end and tapers to a thin end at the other How it works: move the inclined plane, turns the output force at a 90 degree angle Mechanical advantage: divide the length of the wedge by its width ▫W MA = Wl/WW 5 4

Wedge Input force Output force

Screw Inclined plane wrapped around a cylinder How it works: Threads increase the distance over which you exert the input force. Output force pulls screw into object Mechanical Advantage: the closer the threads the greater the MA. ▫S MA = length around threads/ length of screw

Screw Output force

Lever Bar over a fulcrum How it works: input force, pivots on the fulcrum, output force Mechanical Advantage: distance to input force/distance to output force ▫L MA = D IF/D OF Fulcrum Output force (dist) Input force (distance)

Levers Fulcrum Input force (longer dist) Output force (dist)

Types of Levers 1 st Class Lever – Change the direction of input force. The fulcrum is between the output force and input force. Examples: scissors, pliers, seesaw 2 nd Class Lever – increase the force, they don’t change the direction of the force. Examples: door, nutcracker, bottle opener 3 rd Class Lever – increase distance, don’t change direction. Examples: Fishing pole, shovel, baseball bat

Wheel & Axle Two cylindrical objects fastened together and rotate on a common axis. Large radius is the wheel, small radius is the axle. How it works: Increases force, must exert force over a longer distance Mechanical Advantage: radius of wheel/radius of axle ▫WA MA = RW/RA R = 5 R = 0.5

Wheel & Axle Output force Input force

Pulley A grooved wheel with a rope or cable How it works: increase the effect of your input force. Changes the direction of the input force. Mechanical Advantage: number of sections of rope that support the object Input forceOutput force

Pulley Fixed pulley – does not change the amount of force applied, only changes direction Moveable pulley – increase amount of force applied, does not change direction Block and tackle – both fixed and moveable pulleys