People think pulleys increase pulling power.

[shade]

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You know what really grinds my gears? Bicycles. Who do they think they are, with their fancy gears and pedals? Those cogs may be different sizes, but I go just as fast no matter what gear I'm in, how fast I pedal, or how hard I stomp on the pedals. It's all smoke & mirrors on wheels, I say!

 

[Buliwyf]

 

[shade]

Dude ... all that proves is that her shirt really is magic.

 

[NatersXJ6]

Is there a “Best Of” Expediion Portal? This has to be the single funniest / most frustrating thread I’ve ever seen. I say “drink beer every time you see the word “pulley”, and do a shot every time someone repeats an argument point without quoting it”... please don’t post and drive.

 

[shade]

It's spelled pulleye. The second e is silent.

Unless it's attached to a moving anchor point.

 

[NatersXJ6]

If properly lubricated, they should be silent, but may then collect dust.

 

[shade]

Whats difference between pulley and sheave ?
I dont really care. Just doing my part to keep the stupidity going.
Does it have to do with difference between rope and cable ?

Technically, a sheave is part of the pulley - or pulleye, depending on use ... in this thread.

Pulley Block Parts - What are Sheaves?

I'm not sure how multi-sheave blocks (or pulleys) factor into some of the original research in this thread, but I'm willing to learn.

 

[Hopeless Diamond]

Multi sheave pulleyes just allow for multiple pulling segments. In the picture i posted the pulleyes were dual sheeves allowing for 4 segments

Of course all of these calculations are out the window if you're try to do a recovery on a Tuesday with more than 5 elephants in the area

Sent from my Pixel 2 XL using Tapatalk

 

[shade]

Multi sheave pulleyes just allow for multiple pulling segments. In the picture i posted the pulleyes were dual sheeves allowing for 4 segments

Of course all of these calculations are out the window if you're try to do a recovery on a Tuesday with more than 5 elephants in the area

Naturally.

 

[DiploStrat]

All of those who don't believe that multiple pulleys can increase mechanical advantage would be well advised to visit any 18th or 19th century museum ship, e.g. USS Constitution, HMS Victory, et al. Feel free to examine the rigging used to move the sails or lift the guns. Take all the time you need.

(And yes, they can also be used to change direction as well.)

In our Jeep and tree example, assuming that the pulleys themselves are strong enough, the problem is not that our 9,000 lb. winch cannot pull 27,000 lb., or that the cable will break, but rather that with out 9,000 lb. winch pulling 27,000 lb., we risk to break the anchor point or, even more likely, simply move the Jeep.

(The loops of cable are no different than the weaving of multiple strands of wire into a single cable.)

And none if this is new, it goes back literally thousands of years. The ancients were all over levers and mechanical advantage.

 

[Metcalf]

.......aye........

I don't even know where to start back in.

 

[NatersXJ6]

Multi sheave pulleyes just allow for multiple pulling segments. In the picture i posted the pulleyes were dual sheeves allowing for 4 segments

Of course all of these calculations are out the window if you're try to do a recovery on a Tuesday with more than 5 elephants in the area

Sent from my Pixel 2 XL using Tapatalk

If you have more than 5 elephants... you shouldn’t need a winch.

Just because it is punchy Friday... on a tuesday... I have to say that I always thought a sheave was a bundle of wheat used to stab people in prison...

A snatch block... on the other hand... isn’t discussed in polite company.

I’m done being ridiculous now. There was value in this discussion if you sorted through it appropriately.

 

[Essayons]

Dude, seriously, slow down and pay attention. "... the part of the rope you are pulling with..." is the one going off to the side, not either of the ones connected to the mass or the vehicle. This is literally as clear as I can make it.


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This is not what we're talking about. This is the redirected end of the rope being attached to an immovable object, NOT back to the vehicle.

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Randy,
Apparently you didn't read your own reference article...

"Now if you add more wheels, and loop the rope around them, you can reduce the effort you need to lift the weight. Suppose you have two wheels and a rope looped around them, as in the figure below. The 100kg mass (1000 newton weight) is now effectively supported by two sections of the same rope (the two strands on the left) instead of just one (ignoring the loose end of the rope you're pulling with), and this means you can lift it by pulling with a force of just 500 newtons—half as much! That's why we say a pulley with two wheels, and the rope wrapped around it this way, gives a mechanical advantage (ME) of two.

Mechanical advantage is a measurement of how much a simple machine multiples a force. The bigger the mechanical advantage, the less force you need, but the greater the distance you have to use that force. The weight rises 1m, but now we have to pull the loose end of the rope twice as far (2m). How come? To make the weight rise 1m, you have to make the two sections of rope supporting it rise by 1m each. To do that, you have to pull the loose end of the rope 2m. Notice that we can also figure out the mechanical advantage by dividing the distance we have to pull the rope by the distance the weight moves."

Because both ropes are pulling on the vehicle you get a 2:1 mechanical advantage out of the snatch block on a tree. Imagine it like this:

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This is the original example. So clearly if the immovable object isn't going anywhere, and your vehicle can roll then the 100 newtons of weight that can be pulled is the vehicle.
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You need to check your arrogance and actually examine your argument.

Don't confuse arrogance with confusion. I thank Verkstad for jogging my memory in his reply which was totally correct:
"Your effort pulling is 50lbs. Believe it or not, The other 50 comes from the anchor on the loft floor."
It was an example I used if a 100 lb weight was lifted vertically from above but with a pulley fixed to the weight in which the line ran through fixed to the floor above, the other end was pulled from the same location.
This jogged my memory since what he referred to was a traveling block arrangement, but in this perspective(self recovery) the block isn't moving on a double line, but the pulling source does. So yes, using a snatch block on an object and running the cable back to the pulling vehicle will cut the effort in half. I'm glad I got that cleared up.
Now that I've have everyone's attention, does anyone have experience with the Sherpa winches?..

 

[Essayons]

Dude, seriously, slow down and pay attention. "... the part of the rope you are pulling with..." is the one going off to the side, not either of the ones connected to the mass or the vehicle. This is literally as clear as I can make it.


View attachment 525181

This is not what we're talking about. This is the redirected end of the rope being attached to an immovable object, NOT back to the vehicle.

View attachment 525183

View attachment 525184

Thanks for the drawing. That and what Verkstad noted made me realize it was a traveling block configuration...

 

[Essayons]

Hey all: here's a link that can be helpful:
https://www.thecrosbygroup.com/html/en-US/calc/snatchblockrigcalc.htm