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In this situation the distance the lifter must pull the rope becomes twice the distance the weight travels, allowing the force applied to be halved. Note: if an additional pulley is used to change the direction of the rope, e.g. the person doing the work wants to stand on the ground instead of on a rafter, the mechanical advantage is not increased.
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there is enough friction where the rope is pinched between the barrel and the ramp, the pinch point becomes the attachment point. This is considered a fixed attachment point because the rope above the barrel does not move relative to the ramp. Alternatively the ends of the rope can be attached to the platform.
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has an MA of 2 (assuming frictionless bearings in the pulley). Consider a pulley attached to a weight being lifted. A rope passes around it, with one end attached to a fixed point above, e.g. a barn roof rafter, and a pulling force is applied upward to the other end with the two lengths parallel.
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Two ropes laid down a ramp attached to a raised platform. A barrel is rolled onto the ropes and the ropes are passed over the barrel and handed to two workers at the top of the ramp. The workers pull the ropes together to get the barrel to the top. The barrel is a movable pulley and the MA = 2. If
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By looping more ropes around more pulleys we can construct a block and tackle to continue to increase the mechanical advantage. For example, if we have two pulleys attached to the rafter, two pulleys attached to the weight, one end attached to the rafter, and someone standing on the rafter pulling
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the rope, we have a mechanical advantage of four. Again note: if we add another pulley so that someone may stand on the ground and pull down, we still have a mechanical advantage of four.
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Consider lifting a weight with rope and pulleys. A rope looped through a pulley attached to a fixed spot, e.g. a barn roof rafter, and attached to the weight is called a
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creates mechanical advantage, by having the flexible material looped over several pulleys in turn. Adding more loops and pulleys increases the mechanical advantage.
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A velcro strap on a shoe passes through a slot and folds over on itself. The slot is a movable pulley and the MA = 2.
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wrapped around a cylinder. The run over the rise of this inclined plane is the mechanical advantage of a screw.
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The theoretical mechanical advantage for a screw can be calculated using the following equation:
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Examples of rope and pulley systems illustrating mechanical advantage.
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63:*a) being in equilibrium with the moment created by vector force
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Here are examples where the fixed point is not obvious:
357:(Revised 1994 ed.), Courier Dover Publications,
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Note that the actual mechanical advantage of a screw
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How to Dunk a
Doughnut: The Science of Everyday Life
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351:United States Bureau of Naval Personnel (1971),
316:United States Bureau of Naval Personnel, p. 5-4.
75:is translated in a relatively high vector force
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268:: MA = length of slope ÷ height of the slope
47:shown is in static equilibrium around the
223:{\displaystyle MA={\frac {\pi d_{m}}{l}}}
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243:= the mean diameter of the screw thread
384:Mechanical engineering — pulleys
71:*b). The relatively low vector force
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389:Mechanical advantage — video
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354:Basic machines and how they work
20:Beam balanced around a fulcrum
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122:: A screw is essentially an
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51:. This is due to the
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330:Fisher, Len (2003),
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36:- e.g.:
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249:= the
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43:: The
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41:Lever
359:ISBN
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45:beam
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247:l
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69:B
61:A
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