Simple Machines B/Compound Machines C

[hscmom]

Can someone help me on where to get information for the history part of the test. Aside from the Wikipedia paragraph and a couple undescriptive google sites, I have nothing. Thanks

There IS a lot of info on wikipedia that is useful. Check the children's section of the library too. We found a half dozen or so good books there.

Here's a site to get you started answering the question "Who invented the compound pulley?" http://wiki.answers.com/Q/Who_invented_ ... ley#slide2

[Olympus1701]

Correct me if I'm wrong, but efficiency is
Work Output
Force Input

Also, what unit is used to measure efficiency?

[olympiaddict]

It's generally given as a percentage, so in other words it is a unitless quanitity. Since the input and output have the same units, they cancel out.

However it is work out / work in, not force in.

[chinesesushi]

It's generally given as a percentage, so in other words it is a unitless quanitity. Since the input and output have the same units, they cancel out.

However it is work out / work in, not force in.

That doesn't look right. I thought efficiency was AMA/IMA, where AMA is the actual mechanical advantage and IMA is the ideal mechanical advantage?

[Phys1cs]

It's generally given as a percentage, so in other words it is a unitless quanitity. Since the input and output have the same units, they cancel out.

However it is work out / work in, not force in.

That doesn't look right. I thought efficiency was AMA/IMA, where AMA is the actual mechanical advantage and IMA is the ideal mechanical advantage?

I believe work in/ work out is used for finding IMA, and AMA/IMA is used for efficiency

[alpacas]

Hi C Division competitors (and B I suppose could also discuss this) what is the accuracy of your machine so far? Either in grams or percent error, whichever is more consistent- I was kind of envisioning a running discussion like past score threads of boomilevers and other build devices.

[helicpters_rule]

Hi C Division competitors (and B I suppose could also discuss this) what is the accuracy of your machine so far? Either in grams or percent error, whichever is more consistent- I was kind of envisioning a running discussion like past score threads of boomilevers and other build devices.

I think a thread would be great my lever has and average percent error of less then one percent and in case anyone is wondering I usually get below 25 seconds but in my last competition I did it in 17 seconds and had a 0 percent error so I was pretty happy with my lever. One of my friends gets about 2 percent error and takes about 45 seconds.

[olympiaddict]

Work = force times distance
If a pulley can life 4kg with a 1kg counterweight, then the 1kg mass will move 4 times as far as the 4kg mass will over an interval of time.
any ideal (that is, 100% efficient device) has (work out)/(work in) = 1. (Conservation of energy)
Here it's 4kg * g * 1cm = 1kg * g * 4cm. They're inherently equal in a frictionless device, that's the whole reason mechanical advantage works, it doesn't create energy, just expresses it over more / less distance with more/ less force.

In real life though, there's friction etc, so not all of the energy put into the device "comes out" mechanically, some is lost to heat, sound, so forth. Work is change in energy, so it is clear that efficiency does equal work out / work in. It could not however equal work in/work out, since in real life that number would always be greater than 100%, and a more than 100% efficient device makes no sense.

What you guys were probably thinking of were the relationships
IMA = distance in/distance out
And
IMA = force out/force in.


However efficiency is also AMA / IMA, which intuitively makes sense given what I wrote above.

[vvheaton]

I uploaded a test for Compound Machines today, but am not sure if I have to link it to the Text Exchange Page. Any help there?

[chinesesushi]

I uploaded a test for Compound Machines today, but am not sure if I have to link it to the Text Exchange Page. Any help there?

I don't see it under Test Exchange?