How nerds pass the time

18:27 Ryan: Megan says you are now unsure of the physical possibility of the swinging-cage scenario in Pirates of the Carribean
me: atleast in that scenario
18:28 I think the force that you could apply would be less than the force of gravity near the end of the swing and you could not reach the edges
18:29 Ryan: huh, the force you apply would be less than the force of gravity?
18:30 me: gravity damps the swing, yes, from reaching a larger amplitude
side to side is easy, but the upswing makes it more difficlut
18:31 Ryan: oh, so in the movie did they go so far that the rope was horizontal?
me: atleast 30 to 40 degrees
18:33 Ryan: but a swing can go that high
me: I don't think it would scale
18:34 there would be a lot of drag on the ball cage to slow you down
Ryan: air drag?
18:35 but there would be more muscle power too
me: if you could make it work harmonically, together
18:36 I'm trying to imagine what actions you use on a swing
it seems like you apply force through the whole or half of the swinging motion
18:37 Ryan: I did a swinging experiment awhile ago
me: in a cage over a ravine?
Ryan: heh, No, on a swing. I thought that the swinging ball-cage would be possible
18:38 I think you move on a swing by moving your legs in the opposite direction from how they would naturally sway if you relax them
so, your legs do work
me: newton's 3rd law?
18:39 like 2 little rockets
Ryan: hmm? what's like 2 rockets? your legs?
18:40 me: you move them in the opposite direction and it pushes you
18:41 Ryan: but ... you swing them forward when you're about to move forward
me: I'm still concerned about the scale of the problem. Does it work for a cage over a ravine
2 stage swinging?
18:42 Ryan: when you're at the rear of your swing, you push your legs forward and lean back, somehow propelling yourself forward
me: you also pull on the chains or ropes, torque pulling you forward
Ryan: Yes, I had a torque theory for awhile
18:43 me: nothing in a cage though
Ryan: To be honest, I think swinging may be more complicated than you would think ...
Either that or I have done too much subatomic stuff and am rusty on my basic newtonian dynamics
18:44 me: yeah. I have to study that again for my qualifiers
Ryan: next time you see a swingset, go conduct an experiment
18:45 me: hmm. I should. se what ways there are to swing. and if I could simulate beign in a cage
18:46 Ryan: I found that, without touching the ground (of course), and without twisting, holding or bending the chain, I could get myself swinging just by swinging my legs back and forth.
me: was there a limit to your amplitude?
Ryan: So torque on the rope doesn't seem to be necessary, though it may enhance the swing
me: i woudl think so
18:47 Ryan: umm, I don't think I explored the amplitude limit
I'm sure I could have gone farther by pumping my legs more, but I was more interested in how I got started swinging
18:48 me: I'll see if I can find a park tomorrow.
18:49 so the module was lost as it was being shipped here. But they found it
Ryan: I know how energy and momentum are conserved, but I have to admit I'm not sure about one thing:
shouldn't the center of mass remain at rest if no external force acts on the system?
does your leg swinging count as an internal or external force?
18:50 me: I don't think the human body would count, since chemical energy is being released
like a bomb
18:51 Ryan: well I'm not so sure. Consider a train at rest on a frictionless railway. If you run back and forth, the train goes in the opposite direction, but the center of mass remains the same
18:52 me: ummm.. I guess the rope isn't part of a frictionless system
18:53 it a harmonic oscillator system
Ryan: that's another thing .. is the friction in the bearing relevant?
18:54 me: yeah, it damps
Ryan: that is, if it were truly frictionless, could you still swing?
18:55 sure it damps a bit, but is that all?
me: hmm. see with the train you had to run back again to return to the same position. but a swing you don't. if you tried you would go nowhere. you only apply "force" half the time
gravity does the rest?
18:56 or you apply force when gravity is working with you?
18:57 Ryan: but gravity can't do any net work on you if you always return to the same height
me: apply some to move and then more on the down swing to increase your amplitude
but you're doing woek
work
Ryan: yes, you do work .. against gravity, or some non-inertial force?
18:58 me: gravity I would think
18:59 Ryan: hmm, I don't know. Maybe I should change my focus from subatomic to swingset dynamics
19:00 me: you could do a paper on the verification of the escape of pirates from a suspended cage
19:01 Ryan: lol
9 minutes
19:11 Ryan: Thesis will be ""Analysis of the escape of pirates from a suspended cage"
me: Where would you get pirates for the experimental data thoguh?
19:12 Ryan: get eyepatches from the dollar store, and round up some friends
me: I don't know if that would work. I think the pirate would have to be authentic
19:13 Ryan: hopefully such crude approximations of pirates wouldn't detract from the reliability of the data
hmm maybe you're right
19:18 anyway, I gotta go eat now
talk to you later