How Much Power Can Be Saved?

You are asking a question that has no straight answer. The amount of power is something you must choose specific to your design. pulleys and gears etc will save you power for a cetain amount of work but you must expend the same amount of energy so you use less power but over a longer time via the pulley/gear arrangement. So the answer is your choice. You must choose a balance between the amount of power you will use and the time you wish to spend then you can look up the appropriate references for formulas to figure the pulley/gear arrangements you will use.

I agree with rollinshulz i just wanted to add that one pully would only change the direction of force.

I"m not sure you can save power. You can use smaller motors but for a longer period of time so the power equation should allways be balanced.

A pulley system is a force transformer.

Let us say you have 6 pulleys, 3 on a ceiling joist and 3 on a hanging hook with loops of rope going over the pulleys(which we will call frictionless). Since you have a rope on frictionless pulleys it has the same tension through out.

You have the role in one hand and you exert a force of 100 pounds. All the rope in the system is now tensioned to 100 pounds.

Examine to hook to the load.

It has 3 pulleys with 6 ropes, each rope tensioned to 100 pounds. Thus it will lift a weight of 600 pounds.

Let us say you raise that weight 1 foot = 600 foot pounds of energy. The ceiling hook does not move. The rope in your hand is staill at 100 pounds, and since you shorten the rope pength on the hook by 1 foot times 6 ropes, your rope must be pulled a distance of 6 feet to raise the weight. This is the same 600 Foot pounds that liafted the weight.

Of you did it in one second, you will have done just over 1 HP of work (550 foot pounds/second). A rare man could keep up that work load for long, but a strong man could do it for a few seconds.

Add a motor, add more pulleys, and adjust it.

If you had 60 pulleys on the hook and the ceiling = 120 ropes, your 100 pounds would raise 6 tons. But you could not do than in a second, nor could a horse.

If you still had the 600 pound weight the tension would be 600/120 = 5 pounds of pull.

A baby could raise that load, but with the pulling out of 120 feet of rope.

TANSTAAFL

With one pulley a half KG can balance one KG.

One pulley with a half KG (plus or minus) can lift or drop (resp) 1KG very slowly.

With one pulley one KG can lift one KG at 1 G acceleration rate.

I disagree...... with one pulley you can change the direction of the force but you can't balance 1 kg with ½ kg!!

You need a minimum of two pulleys to gain a mechanical advantage of 2, but then you have to do the work twice as long!

School physics...... John.

I think you overlooked placing the pulley at the top of the load and securing one end of the rope to a point overhead. Now if you pull on the rope you will only need 1/2 kg force to lift 1 kg weight. Yes, you do change direction and the pulley halves the force. All this might be clearer if I could post a drawing...

Ooops sorry forgot that one sparkchaser.....

My turn to buy the drinks!!

John

My experience is not to use a pulley. More modern lifting devices such as a chainfall or come-along/puller are designed to meet safety standards for lifting such loads and they also have a braking technology included. Rope and Pulley is a good way to get somebody hurt. Specification on lifting Equiptment is available from the Manufacturing Company. DonnieH

a chainfall is a pulley made with chain. Pulley systems are quite safe if you do not let the rope/chain go, and most have locking methods, such as a tie point for the rope/chain.

"are any other type of mechanism"? is part of the question. my experience is, it is very hard trying to secure the rope with one hand and while pulling/holding on a rope with the other hand. Pulley's have a place in history but more modern technology still requires the same technology to calculate the Energy required move/lift the load.The Strength/Energy of the person pulling on a rope is hard to calculate as it does not remain constant while the load does. I prefer the other type of mechansim, chain pulleys over rope pulleys except on sail boats. I have seen nothing so far as energy loss due to friction from the ropes bending over one or multiple rope sheaves under load, or the enery loss from the gear mechanism using a Chain Pulley. The answers to any question will vary and this is a great site to view all of them.DonnieH

Hi

It will be better if you will; specify it energy insteed of power.

You can not save energy by any method, infact you may end up loosing some of of energy due to efficiency loss.

It is the mechanical advantage that you get by adopting any such system.

the ammount of energy requird can be calculated by simple formula mxgxh.

again it depends at what height you want to lift the article.

to lift 1 meter of height and 1kg of mass you need 1x1x9.8=9.8 joules.

now if you want to lift this mass in one second then you need the power of 9.8 watt. if you want to lift this mass in 10second then you need the power of .98 watt.

Guess i hv explained.

Rakesh

Who was it said, "give me a long enough lever and I will move the world", archimedes??

Well a pully system is an analog of a lever system. You trade motion at a lower force for high force with low motion.

In all cases the work is the same.

Pulleys, gears, and levers will not change the amount of power used, if you use the word "power" in its technical sense, as in horsepower or watts. But aside from that, you can use multiple pulleys to obtain very high force multiplication. With pulleys and rope, eventually the accumulated friction of so many twists and turns and so many axles will add up, but you can certainly lift 50 Kg with a force of only 1 kg on the end of a rope lead through a system of pulleys. In practical terms, 10:1 or 20:1 is about as high as you see in use.

The trade off that comes about from conservation of energy is that to move a heavy load one meter through a 20:1 pulley system, you will need to pull the rope 20 meters.

If you want to see pulleys in use, befriend a sailor.