Understanding deflection force
Deflection forces can be used to provide simple and powerful mechanical advantage . In the image below , four rescue crew members are holding a rope taut while the crew leader tries to deflect the rope in the middle .
Whilst the four crew members could easily lift their crew leader under normal circumstances , they are unable to resist the deflection force applied to the centre of their static rope .
The distance that the rope has been deflected sideways in the middle by the crew leader ( green ) is much larger than the distance that the crew members have been pulled in ( red ). Working out this ratio will show you how much larger the force is at either end .
This shows a five to one increase in force . ( Diagram not to scale !) Deflection forces will be larger when :
• The rope is under more tension before the deflection force is applied
• The rope is more static ( ropes with more elongation will stretch , thereby decreasing the included angle )
• The distance between the anchor points is greater .
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