Harry K wrote:
(Doug Miller) wrote in message . com...
In article , (The Other Harry) wrote:
[On Wed, 10 Mar 2004 14:08:41 GMT, "Michael Daly"
wrote:]

If you don't beleive it, get a spring balance and test it.
You can use a light rope and something weighing only 10lb
or so.

I might just do that.

You'll be surprised. I was -- when I read the first post this morning that
stated it would be 80 lbs, my first thought was "what a bunch of crap". But
the poster's reasoning seemed valid to me. So I tried it, using a reasonably
good spring balance, a toolbox, and a rope. The toolbox, just hanging from the
spring balance, weighed 28 lbs. Then I tied the rope to the toolbox handle,
passed it through the hook on the balance, stood on one end of the rope, and
lifted the toolbox by the balance: 55 lbs.

I suspect your 55 lb reading was while lifting thus getting friction
force added to the weight. Let it all come to rest and you will be
seeing 28 lbs (plus weight of rope from spring hood to the load).

Nope, he got it right. Consider the reversed situation: a rope fixed to a
ceiling, running down to a pully attached to a load and then up to another
hook. The tension in the rope is going to be half the load, since it's
supported by two ropes and the load is equally supported. This is the
exact same situation with a single overhead pully lifting a load: The
force at the ends of the rope are half the force on the pully, or, force
on the pully is twice the load, which isn't suprising: if you wanted to
use free weights to simulate the loading, you'd have to put a 40lb wieght
on the other end to support the 40 lb pot with a total weight supported of
80lb.



John
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