Week 23 - Work and Efficiency
Completion requirements
Week 23 - Science, Society and the Environment
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Lesson 9
Read pages 287 - 292
Lesson 9:
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Work is done when:
- a force is applied to an object, and
- when the object moves in the general direction of the force.
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That means if you go out and try to move a semi-trailer truck and you push and push until you feel like your going to have a heart attack but don't move the truck - you didn't do any work! |
The reason why the word 'work' has a very exact meaning is because it describes a mathematical formula.
Work (W) = effort force (F) x distance (d)
W = F x d
W = F x d
But before we go over the math there are a few things you need to know. If you have measured the force of gravity pulling on the object with a force meter your measurement will already be in newtons. But if you only know the mass (kg) of the object then you will have to convert it into newtons.
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Force is measured in newtons (N).
If you want to calculate the force of a mass (aka its weight), you need to think about this formula:
Force = mass x acceleration
If you want to calculate the force of a mass on Earth, the acceleration is the pull of gravity on that object.
Force of Gravity = 9.8 m/s2
However, we will just round it up to 10.
To convert mass (kg) to weight (N), multiply by 10. For example: Convert 20 kg to Newtons. 20 kg x 10 = 200 N |
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We measure energy in Joules (J) .
1 Joule = 1 N of force moving through 1 metre (m) |
Now lets look at the example below:
Now it's your turn.
Exercise 3.2: Calculating Work|
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Work In Equals Work Out
It is very important for you to realize that any machine you are using to do a job can only make the work easier. But the amount of work you are doing to complete a job remains the same. Whether your using a pulley, an inclined plane (a ramp) or any other machine, you must put the same amount of work into the machine that you want to come out the other end.
Then why do we use machines if we still have to do the same amount of work? Because simple machines allow us to do the work easier. In other words, the machine allows us to do the work over a longer distance and that allows us to use less effort force. Look at the formula below, if the work (W) remains the same and the distance (d) over which you do the work goes up, then the effort force (F) has to be less. Therefore the work you had to do was easier to do because you did it over a longer distance.
It is very important for you to realize that any machine you are using to do a job can only make the work easier. But the amount of work you are doing to complete a job remains the same. Whether your using a pulley, an inclined plane (a ramp) or any other machine, you must put the same amount of work into the machine that you want to come out the other end.
Then why do we use machines if we still have to do the same amount of work? Because simple machines allow us to do the work easier. In other words, the machine allows us to do the work over a longer distance and that allows us to use less effort force. Look at the formula below, if the work (W) remains the same and the distance (d) over which you do the work goes up, then the effort force (F) has to be less. Therefore the work you had to do was easier to do because you did it over a longer distance.
Machines allow us to do the same
amount of work easier - using less force!
Wow... Cool!
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