5.3 Simple Machines

6 Types  Lever Pulley Wheel and axle  Inclined Plane Screw Wedge

Lever  A bar that is free to pivot about a fixed point (fulcrum)  Fulcrum: the fixed point  Effort arm: distance from the fulcrum to where the effort force is applied.  Resistance arm: distance from the fulcrum to where the resistance force is applied

3 Classes of Levers  1 st class  2 nd class  3 rd class

First Class Lever  Used to multiply force, always changes the direction of the applied force. Ex. Screwdriver used to pry paint can lid  Fulcrum is in the middle

Second Class Lever  Always multiplies force – does not change direction of force. Ex. Wheelbarrow  Resistance is located between the effort force and the fulcrum

Third Class Lever  Increases the distance over which the resistance force is applied. (Does not multiply force) Ex. Baseball bat or hockey stick  Effort force is between the resistance force and the fulcrum.

Mechanical Advantage  Lever IMA = length of effort arm length of resistance arm Making the effort arm longer increases the IMA.

Pulley  Fixed Pulley: modified first class lever IMA = 1 Attached to ceiling or wall Changes direction  Moveable Pulley: Multiplies force IMA = 2 Distance you pull is twice the resistance distance

Pulley (cont.)  Block and Tackle System of fixed and moveable pulleys IMA = # of supporting ropes

Wheel and Axle  Machine with 2 wheels of different sizes that rotate together (gears) Ex. Door knob  IMA = radius of wheel radius of axle Can be increased by making the wheel larger

Inclined Planes  Sloping surface  Reduces the amount of force required  IMA = length height *the longer the ramp the less force required

Screw  Inclined plane wrapped around a cylinder.  The closer together the threads, the easier to screw into wood

Wedge  Inclined plane with one or two sloping sides  Changes the direction of the effort force.

Compound Machine  Two or more simple machines used together. Ex. Can opener Car