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Simple Machines Overview

Mecahanical Advantage
Levers

     There are three main types of levers: class one lever (left), class two lever (middle), and class three lever (right). Every lever has an imput force (effort), output force (load), and a fulcrum.  Levers also have mechanical advantage.  The formula specific to finding the mechanical advantage of levers is the input arm divided by the output arm.  The input arm is the length between the fulcrum and the input force, while the output arm is the length between the fulcrum and the output force.

Second Class
Third Class
First Class

The image above is a first class lever. A first class lever will always have its fulcrum in the middle, and on either side it will have the input force and the output force. 

Below is a second class lever. The fulcrum is on one end and the output force is between the fulcrum and the input force.  The input force ison the opposite end of the fulcrum.  

Above is an example of a third class lever. It is really similar to a second class lever. The fulcrum is always on the opposite side to the load and the effort is in the middle. Some examples of these would be a fishing pole, a hammer, and a base ball bat. A third class lever is not present in our machine.

Every simple machine has a mechanical advantage.  Dividing the output force by the input force on a simple machine is how to find the mechanical advantage of that specific machine.

     Simple machines are used to make every day jobs easier.  usually, they do this by decreasing the amount of force necessary to move objects with a great mass.

    A simple machine is a system in which one can put in an effort and move a load.  Simple machines are pulleys, wedges, wheels and axles, levers, incline planes, and springs.

Why do we use simple machines?
What are they?

For more information on levers, click here

Single Fixed Pulley
Pulleys

Just like a lever, there are three main types of pulleys: the fixed pulley, the movable pulley, and the compound pulley.  Pulleys make it easier to lift objects by changing the direction of the force.  A pulley is a simple machine, therefore it has a mechanical advantage.   The MA formula for pulleys specifically is the input distance or input arm divided by the output distance or output arm.  Another way to quickly find the mechanical advantage of a pulley is by using the MA formula for all simple machines: MA=output force divided by input force.

To the left is a single fixed pulley. The single fixed pulley is the simplest of the three pulleys.  One side of the rope shown on the left is pulled down, which raises the object that is on the other side of the rope.  This pulley changes the direction of the force you exert by pulling, therefore you can pull down and move an object up.  

Compound Pulley

Compound pulleys are also known as "block and tackle" pulleys.  They are a system of several pulleys working together with a single rope that must be pulled to make the system function.  This type of pulley reduces the effort needed to lift the load by more than half the weight of the load.  The disadvantage to this pulley system is that with more pulleys, the longer the rope has to be.  This means that to move the load a small distance, one must pull a much greater amount of rope, even though it would be easier because less force is required.

To the right is an image of a movable pulley.  Movable pulleys are different from single fixed pulleys because they move with the load and they include multiple pulleys, not just one.  Movable pulleys make it so that less effort is used pulling up the load.

For more information on pulleys, click here.

Movable Pulley
Wheel and Axle 

A wheel and axle is composed of a wheel and an axle, which is a rod that connects to the wheel.  When the rod turns, so does the wheel.  The mechanical advantage of a wheel and axle can be calculated by dividing the radius of the wheel by the radius of the axle.  The smaller the axle with a bigger wheel, the higher the mechanical advantage.

For more information on wheels and axles, click here.

Springs are great for storing and absorbing energy.  A typical spring is generally a tightly wound spiral or coil of metal.  Springs can stretch when pulled and when there is no more force being exerted on them, they go back to their original position.  Some springs are what is called "elastic," which means that they stretch bcause they are made of elastic.  The input force on a spring is the force that the spring is pulled apart with.  The output force of the spring is the spring's resistance to being pulled.  The mechanical advantage of a spring is the output force didvided by the input force.

Springs

This is an image of a rubber band.  Rubber bands are springs because they can store and absorb energy.  A rubber band is an elastic spring.

Above: a typical coil spring

For more information about springs, click here.

An incline plane is a ramp, but usually it is used to move objects up.  The mechanical advantage of an incline plane is outout force divided by input force.  The other MA formula that is specififc to incline planes is the ramp length divided by the ramp hight.

Incline Plane

For more information on incline planes, click here.

Wedge

A wedge is basically two incline planes put back to back.  They are thick on one end and narrow on the other.  Wedges are driven between two objects to either separate them or secure them.  The mechanical advantage of a wedge is the length divided by the width, just like with an incline plane.

 

 

For more information on wedges, click here.

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