Ethan at Starts With A Bang did a nice post the other day on an old chestnut - why you can't touch your toes if you're backed against a wall.
It is a simple physical argument: when you bend to touch your toes, your center of gravity moves forward, so to stay balanced your butt must move backwards. Wall blocks this.
Non e pur si muove.
This is a good exercise to try on kids, so, lo, I did.
But...
As the Dynamic Boy and Dynamic Girl lined up to to try it, I mischievously said:
"you won't be able to do it, but there is a trick..."
Kids quickly discover the problem, and Dynamic Boy braces hands on floor and touches toes. He then starts experimenting with different contortions to accomplish this.
I had thought of a limitation of the assumption of the problem, and figured a (theoretical) way around it...
uh, oh.
After a couple of tries, by the kids, the Dynamic Wife gets up with a smile, and says "let me show you the trick".
She put her heel and butt against the wall, smoothly touches her toes with both hands without putting her hands on the floor and with heels and butt remaining in wall contact at all times.
She is quite amazing, and this is not at all the trick I had in mind.
The Dynamic Girl, who established the problem in a single try and had been watching her brother, now smiles, goes to the wall again, and touches both her toes with both hands, but with a different trick then her mother has come up with!
Damn, they're good.
The Dynamic Boy tries both tricks and several hundred other ways of moving up and down for the next while.
Much later, much much later, I go to a wall and try the trick I actually had in mind - I can't do it, though theoretically it must work.
I don't have the combination of musculature and bravado to attempt it. Can't let myself go enough, literally. I suspect one of the kids does though...
Did I mention I am a theorist?
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There appears to be some sort of mismatch with the links... the one you list as going to "Starts With a Bang" takes you to Discover.com
Also, what were the tricks? I'm dying to know!
I'm guessing the tricks involved Modifying Newtonian Gravity...
I'm guessing the tricks involved Modifying Newtonian Gravity...' yes.
The trick I figured out as a teenager was to lie on the floor with my butt touching the wall and my feet pointed toward the ceiling. Then touching your toes is a simple matter of sufficient abdominal strength (which I no longer have). You could make things a little easier on yourself by sliding your heels a bit closer to your butt.
oops, link fixed - forgot to flush cut'n'paste buffer
My wife took the "heel and butt against the wall" instructions literally, but smoothly bent her knees while doing so and touched her toes.
Our daughter went sideways - she does gymnastics and is of the age where you can do this - so with her hips pushed to one side but against the wall she could reach both hands down to touch her toes from the side
My theory, was based on two issues: the simpler one is that your feet have a finite length and if you can torque off your toes you can, in principle, hold off the torque of gravity pulling your center of gravity forward - this is mentioned in Ethan's comments, it requires considerable strength and probably longer feet than I have, at least in proportion...
The other way around it, is that the force diagram is static; so if you touch your toes rapidly, you ought to be able to do so and recover to upright, before gravity has had a chance to accelerate your body too far - again this requires strength, to provide the restoring torque and get back up before toppling, and you have to committ, fast and hard - I may try it on a gym mat one day, or convince one of the kids to try it, I am probably getting too fragile for this stuff.
Off topic, but this reminded me of "beer walking" described in "Heart of a Solder" by James B. Stewart.
With your heels against the wall and a beer can in each hand, bend forward so the cans touch the floor. Then use the cans to walk your hands away from the wall until you are in a push-up position. Leave one can as far from the wall as possible. Then use the remaining can to support your weight as you move that can back toward the wall and return yourself to a standing position. At no time may any part of your body other than your feet touch the floor. The one who deposits the can furthest from the wall is the winner.
Make that "Heart of a Soldier" with an "i."