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What is a MACHINE?

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by

Racheal Haley

on 25 October 2013

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Transcript of What is a MACHINE?

What is a MACHINE?
Mechanical efficiency compares the work output to the work input. The closer the mechanical efficiency is to 100, the better the machine is!
How do machines help?
Most people think that machines help you because they increase the amount of work being done.
THIS IS NOT TRUE!
A machine is a device that makes work easier by changing the size or direction of a force
Main Points
1. A machine makes work easier by changing the size or direction (or both) of a force!
2. A machine can increase force or distance, but not both.
3. Mechanical advantage tells how much a machine multiplies force.
4. Mechanical efficiency compares work output to work input
5. Machines are not 100% efficient because of friction.
For a machine to work, you must do work on the machine so that the machine can do work on something else.
The work that you do on the machine is called the work input.
The work done by the machine on an object is called the work output.
Work output can never be greater than work input!
Machines DO allow force to be applied over a greater distance. This means that less force is needed for the SAME amount of work!
For example, say you had to get a really heavy box into a car. If you lift a box that weighs 450 N straight up a distance of 1 meter, it requires 450 J of work. But if you use a ramp that is 3 meters long to get the box into the car, you only have to apply a force of 150 N to get the same 450 J of work!
Remember that machines make work easier by changing the size or direction of the input force.
Mechanical advantage is a number that tells how many times a machine multiplies force
Mechanical advantage is calculated by dividing the output force by the input force.
MA = (output force/input force)
Example Problem:
A grocer uses a handcart to lift a heavy stack of canned food. Suppose that he applies an input force of 40 N to the cart. The cart applies an output force of 320 N. What is the MA?
MA = (output force/input force) = (320N/40N) = 8
To calculate ME:

ME = (work output/work input) x 100
Example Problem:
What is the ME of a machine whose work input is 100J and work output is 30 J?
ME = (work output/work input) x 100 = (30 J/100 J) x 100 = 30%
Why do you think machines can't be 100% efficient?
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