Bloody Newton's 3rd law and the naughty lifter

  • Thread starter ddr
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  • #1
You know what is lifter right. The tool you use to lift heavy objects.
How does the 3rd Newton's law (action force = - reaction force) suit in it?What about conservation of energy?
 

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  • #2
Jonathan
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I can't tell what you're asking. By lifter, do you mean pulleys?
 
  • #3
Originally posted by Jonathan
I can't tell what you're asking. By lifter, do you mean pulleys?
I mean something like the figure on:

http://www.geocities.com/dr_physica/sf.htm
the fig is:coed.jpg
 
  • #4
Jonathan
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I see what you mean, lever. I can't anwser though, I don't understand your question or what he is talking about in the paragraph above the picture, sorry.
 
  • #5
russ_watters
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Originally posted by ddr
How does the 3rd Newton's law (action force = - reaction force) suit in it?What about conservation of energy?
It sounds like you have an idea here. So you tell us. What about conservation of energy?

Or better yet, why even bother with energy? If you take a static view of a lever, there is no energy involved, just forces. Add 'em all up and they equal zero. Its pretty simple.
 
  • #6


Originally posted by russ_watters
It sounds like you have an idea here. So you tell us. What about conservation of energy?

Or better yet, why even bother with energy? If you take a static view of a lever, there is no energy involved, just forces. Add 'em all up and they equal zero. Its pretty simple.

I'll talk about the fug coed.jpg on my site:
http://www.geocites.com/dr_physica/sf.htm

as it's obvious |Fa| <> |Fr| and |Da| <> |Dr| but...
if you want to make |Fa|=|Fr| then you'll have to make |Da|=|Dr|
it's so cause Ea = Fa x Da = Fr x Dr = Er.
the equation Fa x Da = Fr x Dr means:
smaller distance coresponds to larger force and
larger distance coresponds to smaller force.

Newton III is special case of my saying and it is when |Da|=|Dr|
 

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