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How do machines work?. What is a machine? Allows you to do work in a way that is easier Can be quite simple A machine changes at least one of three factors…

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Presentation on theme: "How do machines work?. What is a machine? Allows you to do work in a way that is easier Can be quite simple A machine changes at least one of three factors…"— Presentation transcript:

1 How do machines work?

2 What is a machine? Allows you to do work in a way that is easier Can be quite simple A machine changes at least one of three factors…

3 The 3 Factors of Work 1.Amount of force you exert 2.The distance over which you exert your force 3.The direction in which you exert your force

4 Input and Output Forces Remember… when you use a machine to do work, you exert a force over some distance. The force you exert on the machine is the input force. The force the machine exerts on an object is called the output force.

5 The output work done by the shovel can never be greater than the input work done by the gardener.

6 Input and Output Work Input force times input distance is called the input work. – Done by the person – Think “I” do input work Output force times output distance is called the output work – Done by the machine

7 The output work done by the shovel can never be greater than the input work done by the gardener. Input work and output work can vary depending on the distance the force exerted. Small input force exerted over a long distance = large output force exerted over a short distance

8 Making Work Easier By Changing Force, Distance or Direction

9 Changing Force

10 Changing Distance

11 Changing Direction

12 Mechanical Advantage Mechanical advantage is the number of times a machine increases a force exerted on it. – Think: “How was the force changed?” MA OF IF No units! : )

13 Mechanical Advantage If MA is over 1: – Force is multiplied! (output force more than input, output distance is less) If MA is less than 1 – Distance is multiplied! (output force less than input, so output distance is more) If MA = 1 – Machine only changes direction – force and distance are the same for input and output

14 Efficiency of Machines Assuming the input work is exactly equal to the output work is ideal, this is not always the case The efficiency of a machine compares the output work to the input work. Efficiency is expressed as a percent. The higher the percent, the more efficient the machine is.

15 Efficiency of Machines What may be the cause of having a less efficient machine? Consider the difference between a new pair of garden shears and an old rusty pair of shears.

16 Efficiency of Machines To calculate the efficiency of a machine, divide the output work by the input work and multiply the result by 100 percent.

17 Calculating Efficiency

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19 Real vs. Ideal Machines An ideal machine is 100% efficient. – Does not exist! A real machine is less than 100% efficient.


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