They do not reduce the work needed to lift an object, they spread the work out over a longer distance. A pulley with a reduction of 4:1 will make it so you have to pull 4 feet of rope to move the object you’re lifting 1 foot. However, it will only require 1/4th the amount of force to do so. You’re still doing the same amount of work, you’re just doing it over a longer distance.
It doesn’t reduce overall work required. You can lift something twice as heavy while maintaining the same perceived weight of the two objects, but you’d need to pull it twice as far to lift it to the same height.
Thanks to the pulley, your one rope is now two ropes (as far as the downward force on the thing you’re trying to lift is concerned) so each rope only needs to support half the amount of weight.
This redistribution of weight reduces the force needed to lift the object.
The pulleys are multiplying the distance you move the rope so you might pull on the rope for a distance of 10 units to raise the weight 1 unit. SO the force required to move the weight is less, but the “work” done is the same.
It’s like climbing up stairs vs climbing up a rope/pole. The work gets broken up into smaller chunks that take in a longer amount of time to get done, so since we can’t produce a force of 1000 all at once it gets broken down to 100 ten times
Let’s say you need to move 100lb. There are a bunch of stacked 5lb weights on a wooden palette. Would you rather try moving all 100lb at once or move as many 5lb weights as you can making multiple trips?
Pulleys essentially sacrifice the weight required to lift something by ADDING distance needed to move something.
The pulley accomplished this by “looping” rope into a sort of a circle. If we count how many “threads” of rope are in this circle by counting from left to right, we can figure out the Mechanical Advantage this system gives. A fancy way for saying how many more trips we need to make to move the weight, BUT we make the initial weight lighter by the same amount.
If a pulley system has 2 “threads”, then we double the distance and half the weight needed.
If a pulley system has 10 “threads”, then we have to move the distance ten times, but the object is ten times lighter per trip.
They allow you to reduce the force required to move a load, but you have to apply that force for longer. It is the same amount of work applied, set by the Potential Energy equation U=mgh for a straight lift.
So, for instance, the old Dutch warehouses had winch points up in the attics. Using a high ratio block-and-tackle, a single person can lift a large load personally, but they have to move a lot to get it there.
Similarly, you can source a small motor to move a large load. It just takes time to move it.
It also spreads the load across each cable, though the blocks and attachments have to be rated for the full load.
Comments
They do not reduce the work needed to lift an object, they spread the work out over a longer distance. A pulley with a reduction of 4:1 will make it so you have to pull 4 feet of rope to move the object you’re lifting 1 foot. However, it will only require 1/4th the amount of force to do so. You’re still doing the same amount of work, you’re just doing it over a longer distance.
It doesn’t reduce overall work required. You can lift something twice as heavy while maintaining the same perceived weight of the two objects, but you’d need to pull it twice as far to lift it to the same height.
Thanks to the pulley, your one rope is now two ropes (as far as the downward force on the thing you’re trying to lift is concerned) so each rope only needs to support half the amount of weight.
This redistribution of weight reduces the force needed to lift the object.
The pulleys are multiplying the distance you move the rope so you might pull on the rope for a distance of 10 units to raise the weight 1 unit. SO the force required to move the weight is less, but the “work” done is the same.
It’s like climbing up stairs vs climbing up a rope/pole. The work gets broken up into smaller chunks that take in a longer amount of time to get done, so since we can’t produce a force of 1000 all at once it gets broken down to 100 ten times
They increase the length of rope you need to pull in order to multiply the force.
So you pull 10 feet of rope to hoist it 1 foot, but you get 10x of the force.
Let’s say you need to move 100lb. There are a bunch of stacked 5lb weights on a wooden palette. Would you rather try moving all 100lb at once or move as many 5lb weights as you can making multiple trips?
Pulleys essentially sacrifice the weight required to lift something by ADDING distance needed to move something.
The pulley accomplished this by “looping” rope into a sort of a circle. If we count how many “threads” of rope are in this circle by counting from left to right, we can figure out the Mechanical Advantage this system gives. A fancy way for saying how many more trips we need to make to move the weight, BUT we make the initial weight lighter by the same amount.
If a pulley system has 2 “threads”, then we double the distance and half the weight needed.
If a pulley system has 10 “threads”, then we have to move the distance ten times, but the object is ten times lighter per trip.
They allow you to reduce the force required to move a load, but you have to apply that force for longer. It is the same amount of work applied, set by the Potential Energy equation U=mgh for a straight lift.
So, for instance, the old Dutch warehouses had winch points up in the attics. Using a high ratio block-and-tackle, a single person can lift a large load personally, but they have to move a lot to get it there.
Similarly, you can source a small motor to move a large load. It just takes time to move it.
It also spreads the load across each cable, though the blocks and attachments have to be rated for the full load.