Got it, good explanation
That makes sense. Thanks.
I wouldn’t want to try to balance the system using friction either. Even if you could accomplish it, it would probably go out of balance often and be a giant headache. I use two ropes for my very basic system.
Yes
That was a good explanation by GBG. The fact that you use a two-rope system probably indicates that you have a good grasp of the situation, without necessarily being able to explain it.
Really we’re talking about the difference between kinematics (the description of how a system moves) versus kinetics (determining the amount of force needed to cause the motion).
A properly designed system is kinematically predictable, i.e. it behaves as it should regardless of the force applied to it. If you pull harder on a well-designed system, you just get greater acceleration, not a different motion.
caridelo , multiple pulleys …
– Last Updated: Jun-24-13 9:54 AM EST –
.... on the same axle is what I have always considered a tackle (block and tackle) , and more than a single pulley in the system is what I have always considered compound pulleys .
I suppose I could add that there is usually a combination of both fixed and movable pulleys in a compound pulley system .
I could be incorrect but I don't think so .
I've always thought that the lifting ability (advantage) of the pulleys is directly related to the number of pulleys in the system and their associated connections to the load .
A block and tackle at top with a single pulley at bottom attached to the load , would increase the advantage more than a single pulley at top and a single pulley at bottom attached to the load ... yet both systems would be compound pulley systems and either system may be considered a block and tackle system . Is this not correct ??
That’s right
You have it right re: compound pulleys - my mistake, and I’ll fix my post above.
Mechanical advantage depends on the number of pulleys, but also their layout, not every four pulley system will give 4:1 advantage. A pretty simple graphic analysis will reveal the ratio. Draw a box around the load and any pulley attached directly to it - the number of ropes leaving the box divided by the number of hoist points gives the ratio.