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Of all the various mechanisms, such as the wedge, the lever,
the gear (etc) the one we hardly ever see is 'Block & Tackle'. Using it is
not straight-forward.
| In the diagram on the right, a 40 kg weight is
attached to the moving block. Each of 4 strands that connect it to the fixed block
supports one quarter of the weight: 10 kg. If you pull on the free end with a
force of 10 kg (plus friction) you can raise the 40 kg weight. |
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Here are some of the features:
 | In a four-pulley system, you can raise the load using one
quarter of the force. |
| In doing so, you have to pull four times as much rope than you
would to lift the load directly. To raise a 40 kg load one meter, you would have to
pull four meters of rope. |
| While you are doing that, the effort (10 kg plus friction) is
constant. |
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Shown left is an example of a Block & Tackle
mechanism. The fixed block (of two pulleys) and the moving block (also of two
pulleys) are kept apart by two spring assemblies. The 'free' end of the rope is tied
to the handle at the top. When the handle pivots, it wraps the rope around the
right pulley, by about 32mm, while the springs compress by 8mm. The only non-LEGO component is the rope: 10 kg test fishing line. |
The insides of it are shown on the next
page.
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