oriol
Well-Known Member
Hi!
This might not apply to something found inside an aircraft, but it might be useful for lifting a heavy weight on the shop. I am having trouble, in understanding how the formulas for a moving pulley/tackle are deduced? I have tried to dig in my books and on the internet, without much success.
If we analize a simple pulley, it is very easy, since both forces have same lever, they cancel each other;
F*r = W*r -> F = W
The problem is, how to analize a moving pulley plus a static one/a tackle?
I have found that the formula used for a "gun tackle", a system of a fixed and a moving pulley is; F=W/2. I can not understand how the formula is deduced?
Or if it can be applied, to a system of multiple pulleys with different diameters, like the equation F=W/n (where n is the number of moving pulleys)?
Analizing the system using a force diagram. I can notice that the tension on the cable is constant therefore equal to R. Then on the pulley in where the weight is attached. The weight is bolted to the center of the pulley therefore the lever is 0, whereas the lever of the cable is r.
Therefore; W = F*r, then F = w/r; r is different from 2 on the standard formula?
Thanks so much for helping me understand basic physics!
Oriol
This might not apply to something found inside an aircraft, but it might be useful for lifting a heavy weight on the shop. I am having trouble, in understanding how the formulas for a moving pulley/tackle are deduced? I have tried to dig in my books and on the internet, without much success.
If we analize a simple pulley, it is very easy, since both forces have same lever, they cancel each other;
F*r = W*r -> F = W
The problem is, how to analize a moving pulley plus a static one/a tackle?
I have found that the formula used for a "gun tackle", a system of a fixed and a moving pulley is; F=W/2. I can not understand how the formula is deduced?
Or if it can be applied, to a system of multiple pulleys with different diameters, like the equation F=W/n (where n is the number of moving pulleys)?
Analizing the system using a force diagram. I can notice that the tension on the cable is constant therefore equal to R. Then on the pulley in where the weight is attached. The weight is bolted to the center of the pulley therefore the lever is 0, whereas the lever of the cable is r.
Therefore; W = F*r, then F = w/r; r is different from 2 on the standard formula?
Thanks so much for helping me understand basic physics!
Oriol
