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Feedback Q&A on Machines

by Ron Kurtus

Readers have sent in a total of 14 comments and questions on Machine issues. They are listed according to date.

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Machines Using levers in health care Ghana
Levers Lifting 250 pound log with a crowbar USA
Machines Centrifugal acceleration in sieving machine South Africa
Pulleys Wants equations for complex pulley system USA

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Using levers in health care

Topic: Machines


March 13, 2010

How does levers applied in health care provition?

abednego - Ghana



There are many devices using levers in health care. The brake on a wheelchair uses a lever. Levers are used to adjust the level and inclination of a hospital bed. Levers are sometimes used to life heavy hospital equipment.

I am sure if you would be observant and look around where health care is being provided, you will see other examples of levers being used.

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Lifting 250 pound log with a crowbar

Topic: Levers


January 18, 2010

This is embarrassing. I am sorry. High School was 30 years ago.
I have a 250 pound log. I have an 8 ft crow bar.

Where must I put that crow bar (fulcrum underneath) so that I only have to push down 70 pounds. I know the closer u are to the ebject the more u can lift. Please give me real numbers. I knowu cross multipy - like ur formulas suggest.

I saw firewood - logs into 21 inches. 200 year old tree 21 in long, weights 150 - 200 or more pounds.

Thank you

RipSaw - USA



You shouldn't be embarrassed, because it is not a straightforward solution.

Let x be the distance from the 250 lb weight to the fulcrum. Then 8 - x is the distance to the 70 lb weight.

250x = 70(8 - x)
250x = 560 - 70x
320x = 560
x = 1.75 ft from the 250 lb weight.

For more information on levers, see:

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Centrifugal acceleration in sieving machine

Topic: Machines


January 18, 2010

"the machine works best when the resulting centrifugal acceleration comes up to the value of 20m/sec squared"

Quote from sieving machine manufacturer comments of the working of machine.

What exactly does this mean ?

Brian - South Africa



When something spins, it creates a centrifugal force, pulling objects outward. Since force is related to acceleration (F = ma), you could call it centrifugal acceleration, although you should also know the radius of the object.

The sieving machine probably requires a rotation speed to create the acceleration and force to push objects to the outside wall.

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Wants equations for complex pulley system

Topic: Pulleys


December 17, 2009

I'm a firefighter doing technical rescue work. We use a double rope system (2 ropes, one mainline, one belay or safety back up rope,no load on it). The question is the load transferred to the belay rope in the event of a failure of the mainline rope. the mainline rope carries all the weight of the rescue, while the belay or safety carries none. I can't seems to find one formula to get an answer regardless of the load(weight) on the rope. I now mass(load)is needed, & distance droped is important, & distance droped (should be a percent of gravity speed(32ft/s(s), but that plugs in where in which formula? 100Kg. rescue, fall 6ft, how much force(load,KG/Lbs) is transfered to the belay line. Or 250Kg rescue and patient falls 6ft. I feel this is important when teaching new rescue tech. the importance of the belay person, who controls the belay line(and will save the rescuer on the rope) at all time. The rope used is a "static" rope, no stretch per say. All the components(pulleys,rope,webbing,carabiners) of the mainline/belay line are rated for only so much force(kg/lbs.), once exceeded you will run the risk of failure of the entire system. Thanks for your/any help in what must seem like a simply question.

gregory - USA



I'm sorry but we don't have any information or equations on complex pulley systems. It is difficult to even visualize your system unless familiar with it. I would think some rescue textbooks would have some details on it.

Best wishes in finding your answer.

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