 # What do machines do? Simple Machines will change the size or direction of a force in one motion. Compound Machines a system of two or more simple machines.

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What do machines do? Simple Machines will change the size or direction of a force in one motion. Compound Machines a system of two or more simple machines (the game mouse trap is a great example).The following is a list of what machines do:

Help us do work more easily. Machines do not save work from being done.
A machine can make the force you put into a machine greater. (ex. Pliers) A machine can change the direction of the force you put in. ( ex. A Car jack) A machine can increase the speed of the force. (ex. Bicycle)

Machines have what is called mechanical energy, the energy of moving things. Some examples of mechanical energy are: wind, moving rocks, and waterfalls. The energy output compared to the energy input is called efficiency.

What is Work? In order for work to be done two conditions must be met:
An object must move. A force must act on the object in the same direction as the object's motion.

When doing work a force must move an object some distance.
The force and distance the object moves must also be in the same direction. Therefore if the object does not move no work is being done. A boy holding a book above a table is not doing any work. He may be exerting a force but NO work is being done. If you are carrying an object the direction of motion and the direction of the force are different. Therefore, no work is being done. Take a look at the following pictures. Is work being done?

Is work being done?

….and here?

Formula for Work Work is measured in units called Joules.
In order to calculate work you need to have the measurement for Force and Distance. Force is measured in Newtons. Distance in measured in units called Meters.

W=FxD

Try: Mrs. Nathan uses 35N of force to push a lawn mower 5 meters. How much work does she do? Mr. Shulman uses 100N of force to push a cart 20 meters. How much work does he do? Max Greene does 150 J of work. He pulls a wagon for 25 meters. How much force is being used?

Power Power is the rate at which we complete work.
How much work we get done in a certain amount of time. For example: Joe and Jessica both have to mow the lawn. Joe completes his 1/2 acre lawn in 1 hour while Jessica completes her 1/2 acre lawn in 3/4 hour. Who is more powerful? Since Jessica completed her work in less time she was more powerful. The unit we use to measure power is the Watt. In order to measure power we need the measurements for Work and Time. Work is measured in units called Joules. Time is measured in units called Seconds.

P= W/T

Try: If it takes 5 seconds for you to do 1000J of work, what is your power output (how much power are you using)? If it takes Mr. Shulman 550J of work to carry a piece of wood for 5 seconds, how much power is he using? It takes Zeek 5 Watts of power to do 245 Joules of work. How long would it take him to work?

The Lever

A lever is a strong support that pivots on a point.
The seesaw is a great example. Below you will find a diagram detailing the pivot point and the support bar.

Fulcrum: point at which a lever is supported
Lever: bar that is free to turn about a fixed point Mechanical Advantage of a Lever - You can find the mechanical advantage of a lever by dividing the length of the effort arm (the side you are pushing or pulling) by the length of the resistance arm (the side with the object). MA = effort arm length / resistance arm length

1. What is the MA of a lever with an effort arm of 2 m and a resistance arm of 0.5 m? MA=4 2. What is the MA of a lever with an effort arm of 12 in. and a resistance arm of 24 in.? MA=.5 Which lever is easier to use? The one in 1 or 2?

Inclined Plane

Some examples are stairs and ramps. Inclined planes along with the other simple machines provide us with an advantage. This Mechanical Advantage is how many times the machine multiplies your effort. The formula for the mechanical advantage of a inclined plane is the length divided by the height. The higher the MA, the easier…but longer the work will be. The lower the MA, the harder…but shorter the work will be.

Try to figure out the MA of these inclined planes:

Pulley

A pulley is a very common simple machine.
Did you ever open or close the blinds in your house? If you did you used a pulley. A pulley has two parts: 1. A wheel that turns on an axle. 2. A rope that runs over the wheel. Click Here for images and examples…or Here

Wedge

A wedge is an inclined plane usually used for cutting.
An axe, scissors or knife are two common examples. The longer the wedge the greater the mechanical advantage.

A wedge can either be composed of one or two inclined planes.
A double wedge can be thought of as two inclined planes joined together with their sloping surfaces outward. Single and double wedges are illustrated below:

This is a wedgie…not a wedge
Not to confuse you!

Screw

The screw is an inclined plane wrapped around a cylinder.
The closer together the teeth the greater the mechanical advantage.

Wheel and Axle

A wheel and axle is made of two parts that turn together.
A screw driver is a great example. The bulb handle is connected to the long axle that turns the screw. The longer the axle the greater the mechanical advantage of the machine.

The mechanical advantage of a wheel and axle is the radius of the wheel divided by the radius of the axle. In the wheel and axle illustrated below, the radius of the wheel is five times larger than the radius of the axle. Therefore, the mechanical advantage is 5/1 or 5.

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