# Mechanical Advantage, Efficiency, and Types of Simple Machines.

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Mechanical Advantage, Efficiency, and Types of Simple Machines.

Machines A machine is any device that helps you do work.
Machines do not reduce the amount of work-they multiply the effort that is applied or they multiply the distance over which the force is applied. Machines can be classified as simple, compound, or complex based on the number of parts. Rube Goldberg Machine

Mechanical Advantage The force you exert on a machine is called the effort force (Fe). The force exerted by the machine is called the resistance force (Fr). Mechanical advantage (MA) is the ratio of the resistance force to the effort force, Fr/ Fe. Ideal mechanical advantage (IMA) is the ratio of effort distance (de) to the resistance distance (dr), de/dr.

Efficiency Efficiency is the ratio of output work to input work.
Due to friction between moving parts, no machine has an efficiency of 100%. Efficiency = Wo / Wi x 100% Efficiency = MA / IMA x 100%

Review If you increase the efficiency of a machine, does the
a) MA increase, decrease, or remain the same? b) IMA increase, decrease, or remain the

Types of Simple Machines
Inclined Plane Wedge Screw Lever Pulley Wheel and Axle

Inclined Plane An inclined plane is a flat surface set at an angle against a horizontal surface. Inclined planes allow you to apply a smaller force by increasing the distance over which the force is applied. As the angle of the slant decreases, the mechanical advantage increases. Some examples of an inclined plane are the playground slide, steps, a ski jump, and a wheelchair ramp.

Wedge A wedge is two inclined planes joined back to back.
When you use an inclined plane to do work, the inclined plane stays still and the object being acted upon is moving. When using the wedge, the object being acted upon stays still and the wedge is moving One end of the wedge tapers to a thin edge and the other end is wide. The longer and thinner a wedge is, the less effort is needed to overcome the resistance force. Examples of a wedge are an ax, the point of a nail, a doorstop, and a knife

Screw A screw is an inclined plane wrapped around a cylinder.
A screw makes work easier by allowing the work to be done over a longer distance, just as an inclined plane does. The distance between the threads is called the pitch. The closer together the threads of a screw are, or the smaller the pitch, the longer the distance over which the effort is exerted, and the more the force is multiplied. Examples of a screw include the lid of your jar of peanut butter, the jack you lift the car with when changing a tire, and airplane propellers.

Levers A lever is a rigid bar that rests on a fulcrum (a fixed point.)
The farther the force is from the fulcrum, the easier it is to work the lever. Levers may change the direction as well as the amount of force. There are three classes (kinds) of levers

First Class Lever A first class lever has its fulcrum located somewhere between the effort and the resistance (load). The direction of force is changed with this type of lever. Applying effort downward moves the load up and applying effort upward moves the load down. Examples of first class levers that you may be familiar with are the playground seesaw, a crowbar, scissors, and pliers

Second Class Lever With a second class lever, the fulcrum is at one end, the effort is at the other end and the resistance is in the middle. With this kind of lever, the direction of effort is not changed. Pushing up on the lever arm pushes up on the load. Common examples of second class levers are a screwdriver, a catapult, a nutcracker, a wheelbarrow, and a stapler

Third Class Lever The fulcrum is at one end and the effort is applied between the fulcrum and the resistance. With this kind of lever, the direction of effort is not changed. The load moves in the same direction as the effort. Examples of third class levers include baseball bats, hockey sticks, tennis rackets, golf clubs, brooms, and fishing poles.

Pulley A pulley is a rope, belt, or chain wrapped around a grooved wheel. The pulley is a variation of the lever. Pulleys can be fixed or moveable. Pulley Examples of a pulley can be found at the top of a flagpole. You raise and lower your window blinds with a pulley.

Fixed Pulley A pulley that is attached to a structure is called a fixed pulley. The wheel of a fixed pulley turns, but the pulley itself does not move. A fixed pulley does not multiply the effort force. The distance you apply the effort is the same as the distance the load moves. A fixed pulley changes the direction of effort. When you pull down on the rope, the load moves up. Pulling down is easier than pulling up because you use your body weight when pulling down.

Moveable Pulley A moveable pulley is attached to the object you are moving. One end of the rope is attached to a fixed structure overhead. The other end of the rope goes down through the pulley attached to the load and then back up to the top. Pulling on the other end of the rope causes the load to move up. The moveable pulley offers a mechanical advantage even though it does not change the direction of effort. The load is supported by rope on both sides of the pulley, which means that half as much effort is needed to lift the load. You must exert effort twice as far as the load moves. The force needed to move an object is less, but the distance through which the force must move is longer.

Wheel and Axle A wheel and axle is a simple machine made up of two circular objects of different size. The axle (a small wheel) is attached to the center of a larger wheel. All wheels need an axle. If the radius of the wheel is two times larger than the radius of the axle, every time you turn the wheel once, the force will be multiplied by two. A wheel and axle can produce a gain in either effort or distance, depending on how it is used. Examples of a wheel and axle can be found in doorknobs, roller skates, and the handles of a faucet.

Review Identify the type of simple machine that each of the following tools are examples of. a) screwdriver b) pliers c) chisel d) staple remover e) wrench

Compound Machines A compound machine consists of two or more simple machines linked so that the resistance force of one machine becomes the effort force of the second. Examples include a pencil sharpener, a can opener, and a bicycle.