Simple Machines Review

Flashcards covering key concepts related to simple machines, work, power and mechanical advantage.

Work

Work is done when an object is moved in the direction of a force.

Calculating Work

Work = force X distance

Work Output vs. Work Input

The machine (work output) always does less work than you (work input) because some of your work is used to overcome friction.

Power

Power is the rate (how fast) at which work is done.

Calculating Power

Power = work / time

Units of Work

Joules

Units of Time

Seconds

Units of Force

Newtons

Units of Mechanical Advantage

None

Units of Distance

Meters

Units of Power

Watts

Purpose of Machines

Machines make work easier by changing the size or direction of a force.

Force/Distance Tradeoff

A machine can have more output force or more output distance but never both.

Inclined Plane

Allows you to use less force.

1st Class Lever

Always changes the direction of the force. OF is greater when you move the fulcrum closer to the load.

2nd Class Lever

You get more force.

3rd Class Lever

You get more distance and momentum.

Wedge

A double inclined plane that moves. It is used to separate or divide objects. you get more force and change the direction of the force

Screw

An inclined plane wrapped around a solid core. The closer the threads are the more force you get.

Wheel and Axle

Consists of two objects of different sizes, one turns the other transferring work. If you turn the larger object (wheel) you get more force. If you turn the smaller object (axle) you get more distance and momentum.

Fixed Pulley

A grooved wheel with a rope that is attached to a permanent structure. It only changes the direction of the force. OF = IF, OD = ID

Moveable Pulley

Moves with the load. You get more force.

Block and Tackle System

2 or more pulleys working together. The more pulleys there are the greater the MA (you get more force).

Compound Machine

Any 2 or more simple machines joined together to do work.

Mechanical Advantage

Tells how much the input force is changed.

Calculating Mechanical Advantage

MA = OF / IF

Fulcrum Placement for Increased MA (1st Class Lever)

There is more MA (output force) when the fulcrum is closer to the load.

Efficient Machine

Some of the work you put into a machine is always wasted because of friction. A machine is efficient if most of the work you put into the machine is output in a useful form.

Mechanical Efficiency: Compound vs. Simple Machine

Compound machines are usually less efficient than single simple machines because compound machines usually have more moving parts so there is more friction and more of the work put into the compound machine is wasted.