Unit 2 Review Session Part 1 Work & Simple Machines

What is Work? Work is applied energy It is equal to the force applied times the distance over which that force is applied. .

What unit of measurement do we use for work or energy? Work and energy are both measured using the unit Joule. 1 Joule = 1 Newton of force applied over a distance of 1 meter.

Mechanical Advantage Having a mechanical advantage means the effort needed has been decreased but the distance over which that effort must be applied has been increased. The amount of work stays the same, its just easier. Mechanical advantage is the ratio of the output force to the input force. MA=Fo / F i

Simple Machines Simple machines provide a Mechanical advantage.

Inclined Plane A plane whose angle to the horizontal is less than a right angle The mechanical advantage can be calculated by dividing the length of the slope by the height of the inclined plane.

Wedge A Wedge is simply two inclined planes put together. It is frequently used to either separate or hold objects together. The Mechanical advantage is determined by the length of either slope divided by the thickness of the thick point of the wedge.

The Screw The Screw is a modified inclines plane. It is simply an inclined plane wrapped around a central cylindrical shaft. The mechanical advantage of a Screw is determined by dividing the Circumference of the central shaft by the pitch of the inclined plane.

Parts of a Lever The effort is the force you put in (input force). The fulcrum is the pivot point of the lever. The load is what you are truing to move (output force).

Levers 1st class lever: the fulcrum is in the middle between the effort force and the load. (ex scissors) 2nd class lever: the fulcrum is at one end the effort force is at the opposite end and the load is in the middle. (ex door)

Levers continued In a 3rd class lever the fulcrum is at one end the load at the other and the effort force is in the middle. (ex broom)

Mechanical advantage of a lever Mechanical advantage of a lever is the ratio of the length of the input arm over the length of the output arm. MA= L i / L o

Wheel & Axel A wheel and axel is simply a lever that has been wrapped all the way around the fulcrum which in tern has been extended to become an axel. The mechanical advantage of a wheel and axel is the ratio of the radius of the wheel to the radius of the axle.

The Pulley A pulley consists of a grooved wheel that turns freely in a frame called a block. A pulley can be used to simply change the direction of a force or to gain a mechanical advantage, depending on how the pulley is arranged.

Fixed Pulley A pulley is said to be a fixed pulley if it does not rise or fall with the load being moved. A fixed pulley changes the direction of a force; however, it does not create a mechanical advantage.

Moveable Pulley A moveable pulley rises and falls with the load that is being moved. A single moveable pulley creates a mechanical advantage; however, it does not change the direction of a force. The mechanical advantage of a moveable pulley is equal to the number of ropes that support the moveable pulley The illustration, shows two rope ends support the moveable pulley. Therefore, an effort force of 50 pounds will lift a resistance force of 100 pounds. The mechanical advantage is 2.

The rate work is done is called power. Power is work (joules) ÷ time (seconds) P=W/t The Unit for power is watt. 1watt = 1 joule/second

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