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PULLEYS AND LIFTING - 2 | |
V. Ryan © 2004 - 2017 | |
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With a single pulley, the pulley must be able to move so that mechanical advantage can be increased. Furthermore, the pulley is turned upside-down. |
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The pulley to the left is suspended and as a consequence the mechanical advantage is increased. This happens because the rope on the left and right of the pulley are both lifting the LOAD, they each lift half its weight. The load is split into 2. The calculation is shown below. |
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VELOCITY RATIO |
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Velocity Ratio (sometimes called movement ratio)- is defined as the ratio of the distance moved by the effort to the distance moved by the load. |
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Using the example above. If the load is lifted 2 metres, above the pulley wheel - the rope on the right hand side must be shortened by one metre and this also applies to the left hand side. Therefore, the effort can be seen to move twice as far as the load. |
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A pulley system with the effort applied from above is
very difficult to use. The most comfortable way to use a single moving
pulley is combine it with a fixed pulley, seen below. This allows the
effort to be applied downwards. |
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