Mechanical Advantage - The Chain Block

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Let's examine Mechanical Advantage:


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Man does not have the physical strength to do heavy work.
In byegone days heavy work was done by beasts of burden such as cattle.
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In modern day man makes use of the 6 so called "simple machines" to do work.

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The main simple machines are:
The inclined plane
The screw & wedge
levers & linkages
wheel & axle
pulley
gears
cranks & cams

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When we use the abovementioned machines we obtain a, so called, "Mechanical advantage" which allows use to do heavy work.

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The formula for mechanical advantage is:

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MA (Mechanical Advantage) = Input / Output

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The answer is normally given as a ratio.
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Lets demonstrate MA with a complex machine that makes use of a number of combined simple machines...the chain block:
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We will ask a child to raise an estimated 1,5 ton vehicle in the air by using a chainblock.
The object of the exercize is to demonstrate MA at work and to calculate the MA achieved.
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First without the chain block:
John: "Pick up the truck Lesego"
Lesego: "Eish!" (The truck does not move at all.)
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Next we will use the chain block but always remember to take safety precautions. Simple machines can move a lot of weight and we need to be aware that such an action could cause someone harm.
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Lesego pulls on the small chain that operates the chain block and up the truck goes!
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The next thing is to find out how MUCH Lesego was given a mechanical advantage by using the chain block.
Lets mark the 6m pulling chain with this yellow masking tape.
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Now lets mark the starting point of how high in the air the truck is before we ask lesego to pull the 6m small chain once around the inner mechanism of the chain block i.e. for 1 full revolution.
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The red arrow shows what the height of the truck was after one revolution of the small chain.

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It measures out to a 60mm lift. (6cm)
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Ok let's go through that again:

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MA = Input / Output

= 6m (pull on small chain) / 6cm (rise of the truck)

= 6000mm / 60mm (both measurements are made to be of the same measuring unit in mm)

= 100mm/1mm

Thus a ratio of 100:1

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The mechanical advantage Lesego obtained by using the chain block is a hundred to one.

She traded distance for power. In other words she had to pull the chain a hundred times further than the small chain for every 1cm she could lift the truck.