Simple Machines

Simple Machines Have few or no moving parts Make work easier Can be combined to create complex machines Six simple machines: Lever, Inclined Plane, Wheel and Axle, Screw, Wedge, Pulley

Mechanical Advantage We know that a machine multiplies whatever force you put into it: - Using a screwdriver to turn a screw - Twisting a nail with pliers - Carrying a box up a ramp instead of stairs **The ratio of the output force (acting on a load ) produced by a machine to the applied effort (the input force). Abbreviated MA

Mechanical Advantage (IMA) Ideal MA: This is the MA of a machine in a world with no friction, and no force is lost anywhere (AMA) Actual MA: This is simply the MA of a machine in the world as we know it - Force is lost due to friction - Force is lost due to wind, etc. Can we have an ideal machine?

Lever A rigid board or rod combined with a fulcrum and effort By varying position of load and fulcrum, load can be lifted or moved with less force Trade off: must move lever large distance to move load small distance There are 3 types of levers

Mechanical Advantage: Lever The mechanical advantage of a lever is the distance from the effort to the fulcrum divided by the distance from the fulcrum to the load For our example, MA = 10/5 = 2 Distance from effort to fulcrum: 10 feet Distance from load to fulcrum: 5 feet

Inclined Planes A slope or ramp that goes from a lower to higher level Makes work easier by taking less force to lift something a certain distance Trade off: the distance the load must be moved would be greater than simply lifting it straight up

Mechanical Advantage: Inclined Plane The mechanical advantage of an inclined plane is the length of the slope divided by the height of the plane, if effort is applied parallel to the slope So for our plane MA = 15 feet/3 feet = 5 Let’s say S = 15 feet, H = 3 feet

Wheel and Axle A larger circular wheel affixed to a smaller rigid rod at its center Used to translate force across horizontal distances (wheels on a wagon) or to make rotations easier (a doorknob) Trade off: the wheel must be rotated through a greater distance than the axle

Mechanical Advantage: Wheel and Axle The mechanical advantage of a wheel and axle system is the radius of the wheel divided by the radius of the axle So for our wheel and axle MA = 10”/2” = 5

Screw An inclined plane wrapped around a rod or cylinder Used to lift materials or bind things together

Mechanical Advantage: Screw The Mechanical advantage of a screw is the circumference of the screwdriver divided by the pitch of the screw The pitch of the screw is the number of threads per inch So for our screwdriver MA = 3.14”/0.1” = 31.4 Circumference = ∏ x 1” = 3.14” Pitch = 1/10” = 0.1”

Wedge An inclined plane on its side Used to cut or force material apart Often used to split lumber, hold cars in place, or hold materials together (nails) NSF North Mississippi GK8

Mechanical Advantage: Wedge Much like the inclined plane, the mechanical advantage of a wedge is the length of the slope divided by the width of the widest end So for our wedge, MA = 6”/2” = 3 They are one of the least efficient simple machines

Pulley A rope or chain free to turn around a suspended wheel By pulling down on the rope, a load can be lifted with less force Trade off: no real trade off here; the secret is that the pulley lets you work with gravity so you add the force of your own weight to the rope

Mechanical Advantage: Pulley The Mechanical Advantage of a pulley is equal to the number of ropes supporting the pulley So for the pulley system shown there are 3 ropes supporting the bottom pulley MA = 3 This means that if you pull with a force of 20 pounds you will lift an object weighing 60 pounds