Section 3: Simple Machines

Chapter 5: Work and Machines

Learning GoalsDescribe the six types of simple machines.

Explain how the different types of simple machines make work easier.

Calculate mechanical advantage.

Simple MachinesSimple Machine: a machine that does work with only one movement of the machine.

LeverLever: a rigid bar that rotates around a fixed point called the fulcrum. The bar may be either independent or attached to another object.

LeverIn use, a lever has both an input force and an output force.

Input Force

Output

Force

Lever First Class Lever:

fulcrum is in the middle of the input and output forces MA may be greater or

less than 1

Ex: scissors, see-saw, crowbar

Input Force

Output

Force

Lever Second Class Lever:

output force is in-between the input force and the fulcrum. MA is always greater than

1

Ex: wheelbarrow, nut cracker, bottle opener

Input Force

Output

Force

Lever Third Class Lever:

input force is in-between the output force and the fulcrum. MA is always less than

1

Ex: tweezers, staple remover, broom

PulleyPulley: a machine that consists of a wheel that turns freely in a frame called a block.

PulleyA pulley can be used to change the direction of a force or to increase input force depending on how the pulley is arranged.

Fixed PulleyFixed Pulley: changes the direction of a force; however it does not create a mechanical advantage. Example: Elevator

Moveable PulleyA single moveable pulley creates a mechanical advantage; however it does not change the direction of a force.

Moveable PulleyThe mechanical advantage of a moveable pulley is equal to the ropes that support the moveable pulley.

Wheel and AxleWheel and Axle: a simple machine consisting of a larger wheel rigidly secured to a smaller wheel or shaft, called an axle.

Wheel and AxleWhen either the wheel or axle turns, the other rotates with it. One full revolution of either part causes one full revolution of the other part.

Wheel and AxleExamples:

Pencil sharpener

Door knob

Faucet handles

Inclined PlaneInclined plane: is a sloping surface

that reduces the amount of force required to do work by increasing the distance over which work is done. The inclined plane makes it easier to

move a weight from a low height to a high height.

WedgeWedge: an inclined plane that has one or two sloping sides. It changes the direction of the input force.

WedgeExamples:

Knife/ax

Door stopper

ScrewScrew: an inclined plane wrapped in a spiral around a post. The threads form a tiny ramp that run upward from its end.

ScrewExample:

Many types of lids

Screws

Compound MachinesTwo or more simple machines operating together.