Simple Machines B/Compound Machines C

hscmom
Coach
Coach
Posts: 242
Joined: March 3rd, 2010, 8:41 pm
Division: Grad
State: CO
Location: Colorado

Re: Simple Machines B/Compound Machines C

Postby hscmom » December 17th, 2013, 7:48 pm

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

:)
Homeschool Science Colorado since August 2008

Olympus1701
Member
Member
Posts: 7
Joined: November 17th, 2013, 4:34 pm
Division: B
State: NY

Re: Simple Machines B/Compound Machines C

Postby Olympus1701 » December 25th, 2013, 3:54 pm

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

Also, what unit is used to measure efficiency?
"No great genius has ever existed without some touch of madness"-Aristotle

olympiaddict
Member
Member
Posts: 175
Joined: August 11th, 2012, 5:17 pm
Division: C

Re: Simple Machines B/Compound Machines C

Postby olympiaddict » December 26th, 2013, 2:11 pm

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.

User avatar
chinesesushi
Member
Member
Posts: 258
Joined: September 17th, 2013, 4:57 pm
Division: C
State: CA

Re: Simple Machines B/Compound Machines C

Postby chinesesushi » December 26th, 2013, 4:51 pm

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?
Never argue with an idiot, they will drag you down to their level and then beat you with experience.
Before you criticize a man, walk a mile in his shoes. That way you'll be a mile away and he'll be shoeless.
You should only create problems, that only you know solutions to.

Phys1cs
Member
Member
Posts: 129
Joined: November 10th, 2013, 6:53 pm
Division: Grad
State: MD

Re: Simple Machines B/Compound Machines C

Postby Phys1cs » December 26th, 2013, 7:40 pm

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

User avatar
alpacas
Member
Member
Posts: 14
Joined: October 4th, 2012, 6:09 pm
Division: C
State: CA
Location: M94

Re: Simple Machines B/Compound Machines C

Postby alpacas » December 30th, 2013, 8:51 pm

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
Member
Member
Posts: 44
Joined: November 16th, 2013, 7:17 pm
Division: B
State: OH

Re: Simple Machines B/Compound Machines C

Postby helicpters_rule » January 2nd, 2014, 6:37 pm

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
Member
Member
Posts: 175
Joined: August 11th, 2012, 5:17 pm
Division: C

Re: Simple Machines B/Compound Machines C

Postby olympiaddict » January 2nd, 2014, 10:42 pm

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
Member
Member
Posts: 1
Joined: January 6th, 2014, 4:43 pm
Division: C
State: UT

Re: Simple Machines B/Compound Machines C

Postby vvheaton » January 7th, 2014, 4:29 pm

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?

User avatar
chinesesushi
Member
Member
Posts: 258
Joined: September 17th, 2013, 4:57 pm
Division: C
State: CA

Re: Simple Machines B/Compound Machines C

Postby chinesesushi » January 7th, 2014, 5:53 pm

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?
Never argue with an idiot, they will drag you down to their level and then beat you with experience.
Before you criticize a man, walk a mile in his shoes. That way you'll be a mile away and he'll be shoeless.
You should only create problems, that only you know solutions to.


Return to “2014 Study Events”

Who is online

Users browsing this forum: No registered users and 1 guest