Today I took a running start at the head of my driveway, locked my legs, and slid around 25 feet down the concrete and into the road. I’m 23 but I felt 7. It was awesome.
It reminded me of an old physics puzzler from my undergrad, which I pose to you now:
A particularly nasty engineering professor has placed you in the middle of a circular arena. You can easily exit at any side of the arena, but the catch is that you sit upon a floor with no friction. No amount of running or clawing will move you; the coefficients are just to low to save you.
The professor, sinister in his teaching methods, tells you that the only way to escape is to remember Newton’s laws of motion. With that, he leaves you to your own devices. All you have are the clothes on your back and the shoes on your feet. How do you escape?
If anyone comments with the correct answer, I’ll update this post. Otherwise, you have something to chew on (don’t google it!).
UPDATE: Craig Winslow in the comments below was the first to get the right answer! Now, can anyone tell me why?
Tie your shoes together at the laces, then throw one while holding the other. You will need to do this repeatedly in the same direction in order to overcome air resistance, but this should make you move opposite the direction you throw.
Remember that you need to apply a force to get the thrown shoe back, that will then return you back where you started from.
I’m a total amateur here- I’ve no idea how to run any calculations or use any equations to solve this…. but I’m gonna jus throw this out there. Could you take off all your clothes/shoes/etc… and place them in a pile next to you? My theory is that since there is absolutely no friction whatsoever, the tiny amount of gravitational pull your pile of clothes exerts on your body would be enough to make you move. Once you move to the pile of clothes, you then move the pile again, in the same direction, and keep repeating this until you reach the edge. Again, I’ve no idea how to calculate the gravity of a small pile of clothes or how long it would take it get you moving, but it might work. Then again, if you’re on an ice skating rink and it’s really cold, you might freeze to death from being naked before you reach the edge…
You guys are on the right track, but going a little bit further than you need to. Here’s a hint: think of Newton’s third law.
Take off your clothes, put them on the floor and holding on to the clothes, the clothes, push back. repeat. ??????
Close!
Well…uhm…. Spread the clothes on the floor, roll over it, repeat ?????
No friction!
Take your clothes one piece at a time a throw them. You’ll move in the opposite direction.
Ding Ding Ding!
That’s the correct answer? Hmmm. * will try to figure out why*
or holding on to the clothes, push back hard… the distance you make is equal to the force that you exert to push yourself back//// he he he…. I’m making my own formula.
Would not the force of the throwing arm move one in the direction opposite that obtained by the throwing of the clothes? How about we just blow REAL HARD?
The force used to throw the clothes acts equally on your body, moving you backwards. I guess you could also blow yourself blue.
What about blowing air through your mouth?
Sure!
Surely if you’re getting that precise though the air you inhale would directly counteract the air you exhale unless you turn your head as close as possible to 180 degrees to breath in (or out)
Do breast-stroke movements with your arms, you can swim through the air albeit very slowly
I still like to slide down my icy driveway, and I turn 49 in a few days. Don;t EVER stop having fun.
Now if I could make my driveway total frictionless, the snow would slide off, I wouldn’t even need to shovel it.
Wouldn’t the clothes-off technique need quite a few attempts? If this is a sizeable ice rink, you’d need to be wearing every item in your closet to physics class to make it work. Plus, how are you supposed to stip without loosing your balance? I think this is the winning answer simply because it end up in people being naked on a frictionless surface. What about lifting a foot vertically, placing it down slightly ahead of you, shifting weight to that foot and repeating? (It sounds like walking but you’re not pushing off)
If the surface is truly frictionless, no you would not to throw very much. I don’t think your “stepping” technique would work, again, because there is 0 friction.
If the Engineering professor were truly evil, he would put in the middle of a frictionless dish/bowl shaped depression. Even then I can see there might be ways to get out, but it would be much more difficult to accomplish.
Assuming you get pressed for a pee and assuming static and dynamic friction is zero. Stand up and take a pee keeping the initial jet as horizontal as possible.
For those not sure p before = p after where p is momentum. Initial p within this system is zero so final p has to be zero as well. So your pee of mass m and velocity v goes one way and you of mass m goes in the opposite direction at a much lower velocity v.
Same principle used for any type of jet or rocket propulsion.
Ladies, a little trickier for you.
^ Best response
Suck air in from one direction, then turn around and blow it out the opposite direction. Do this while peeing and throwing your clothes away from you and you’ll zoom right out, undignified and you’ll probably be banned from skating ever again but it’s probably about the fastest you can get out of there.