Question
Please explain the overall combined effect of pulley applications to cranes
In year 12 and studying engineering. I have been given an assignment on pulley
systems and one section it asks to explain the relationship between the
overall combined effect of pulley applications to cranes. I cannot find
anything on the web or in any books. Any information about the use of pulleys
on cranes would be greatly appreciated. Thankyou.
Belinda
Answer
Hi Belinda
Let me give a little physics background.
Two things that are primarily involved in understanding pulleys are Work and Power.
The formula for work, I believe, is Mass times Distance. You will notice that there is no relationship to time.
This is important because if you move something, it doesn't matter if you take five minutes to do it, or 5 hours, you have done the same amount of work.
Power, however, is related to time. I believe the formula for power isWork divided by time.
This is an important concept, because the application of pulley systems in cranes is no different than the application of a pulley system lowering and raising a bucket of water in a well.
Let us say you moved 5 pounds 5 feet and did it in five minutes. The formula would be 5 x 5 / 5
The product would be the amount of power you used.
Let us say that you moved 5 pounds 5 feet but did it in five hours. The formula would be 5 x 5 / 300 (300 minutes equals five hours)
Obviously if you took five hours instead of 5 minutes you would require 1 / 60 th the amount of power you would have required to do it in five minutes.
This is important, espescially in cranes, becuase if you require a smaller amount of power, you will require a smaller engine, whcih would be cheaper.
A smaller engine would weigh less, which has two benefits. A smaller engine would not require as strong a mounting platform as a larger engine, and if the engine weighs less, the entire crane would weigh less, and could be moved faster and safer. This is important when you consider a crane that is used in a shipyard that needs to move from ship to ship.
I wish I knew a little more of your background, as you may already know much of what I told you.
I would recommend examining and understanding shipyard cranes, as they lift incredible amounts of weight, and will help you understand the absolute necessity of pulley systems.
Consider that if you had to make a motor capable of lifting 50 tons directly, it would be so big and so difficult to maintain, that it would be completely impractical.
http://www.freefoto.com/browse.jsp?id=13-03-1
shipyard cranes
If you want to write me directly, you can E-Mail me at work:
brian.mcclung@impinj.com
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