5 Sep
2011
5 Sep
'11
4:45 p.m.
I got the same 20 lbs in my calculations, but I don't think you get to
double it. If I'm the gent, my hand is putting 20 lbs of force on the
ladies back. At the same time, her back is putting 20 lbs of force on my
hand. When we carry a 20 lb object, we're pulling up with 20 lbs of force
and it's pulling down with 20 lbs of force, but we don't call it 40 lbs of
force.
There's also the fact that despite some of the radial acceleration coming
from centripital force, I suspect some of it comes from the feet.
I will agree that 10 lbf would be easier than 20 lbf, and if we can handle
16 lbf each (or 20 and 12 or whatever), we could go around 4.5 times which
could be even more fun.
On Sun, Sep 4, 2011 at 18:35, Jeff Kaufman <jeff(a)alum.swarthmore.edu> wrote:
John Sweeney wrote:
I think you must be talking about much slower swings than I'm talking
about. Let's say we have two 130 pound people who swing 3.5 times
around in a balance and swing. Physics geekery [1] says it takes
fourty pounds of force to hold the two of them together. I'd much
rather have that split over two people.
Jeff
[1] Let's approximate the dancers as point masses of 130 pounds nine
inches apart. There are 12 counts of swinging after the balance,
so about six seconds. Rotating 3.5 times in six seconds means 35
times in sixty seconds, or 35 rpm. Force here is M*w*w*r, where
M is 130 pounds, w is 35rpm, and r is 4.5 inches. This gives
20lbf for each dancer, or 40lbf total.
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If the lady additionally has their left hand on
the back of the
the gent's right shoulder, then the lady is doing more of the
holding together and the gent can do less.
Centrifugal force is not that great - if you are in balance the
pressure is tiny.