Peeing from a see-saw.

[Sapo]

As seen on this pic:

http://www.rebelart.net/diary/wp-dat...es_vogl_19.jpg

(here is the page full page for those who want to see more of him)
http://www.rebelart.net/diary/johannes-vogl/002905/


Can this be done in real life?

Could I lose enough weight through a single miction* event that a regular playground see-saw will shift balance to a carefully prepared counterweight?

The answer will depend on how well maintained and lubricated the see-saw is, of course. But is it more or less believable for any real life values?



* if you pardon my French.

[Irishman]

What is the average volume of fluid per piss?

Wiki says people average 1 - 2L per day. Take 2 L, = 67.6 fl oz.

How many times a day does the average person urinate? I say 8, so that gives

~ 8.45 fl oz per piss.

1 fl oz of water weighs 29.574 g or 0.0652 lbs

So I calculate 1 piss weighs ~ 1/2 lb or 1/4 kg.

Can you rig a counterweight on a seesaw such that the trigger point is within 1/2 lb (1/4 kg) of your weight?

I say tricky but possible.

(I once puzzled myself and others how my weight could drop ~ 2 lbs within the course of about 4 hours one day - not exercising/sweating profusely, but working indoors in A/C. Finally figured out I had put coins in vending machines - a couple dollars worth. So no, I didn't pee that much. ;-) )

[CookingWithGas]

IMHO no. Yes, with a lot of care you could set the counterweight to be in between your full-bladder weight and your empty-bladder weight, certainly no more than a 20 oz. difference. But I'm not sure you would go from flat on the ground to all the way up from that amount of change.

[ivn1188]

Originally Posted by CookingWithGas

IMHO no. Yes, with a lot of care you could set the counterweight to be in between your full-bladder weight and your empty-bladder weight, certainly no more than a 20 oz. difference. But I'm not sure you would go from flat on the ground to all the way up from that amount of change.

Assuming no mechanical difficulties with the seesaw, why wouldn't it stop only when one end hits the ground?

This is easy to demonstrate using a balance.

[not_alice]

Originally Posted by ivn1188

Assuming no mechanical difficulties with the seesaw, why wouldn't it stop only when one end hits the ground?

This is easy to demonstrate using a balance.

Friction.

[Evil Jon]

Ask mythbusters, this is something they'd try.

[Chronos]

The real problem, I think, is that if it's close enough for peeing to make a difference, it'll also be close enough for small shifts in the person's position to also make a difference.

[Ludovic]

Originally Posted by Chronos

The real problem, I think, is that if it's close enough for peeing to make a difference, it'll also be close enough for small shifts in the person's position to also make a difference.

Come one, now you're just taking the piss.

[TruCelt]

Originally Posted by Chronos

The real problem, I think, is that if it's close enough for peeing to make a difference, it'll also be close enough for small shifts in the person's position to also make a difference.

That's what I was thinking. But I doubt this is a link I want to click on from work. ;-)

How much movement is there?

[ivn1188]

Originally Posted by not_alice

Friction.

Friction is a mechanical difficulty.

The answer to the thought experiment is "yes".

The answer to will this work in the real world is obviously "On which seesaw?". It will work on any seesaw that has less friction than it takes to resist about a pound (1 pint of water) pressing down at whatever distance the seat is from the fulcrum.

[Machine Elf]

Originally Posted by ivn1188

Assuming no mechanical difficulties with the seesaw, why wouldn't it stop only when one end hits the ground?

This is easy to demonstrate using a balance.

It'll depend on exactly where the two centers of mass are with respect to the pivot axis:

-if the two COM's can be connected by a line that passes above the pivot axis, the system will be bistable: it will sit with one mass on the ground until a critical amount of mass is removed from that end, at which point it will tilt until the other end smacks the ground. When I donate blood at the local Red Cross place, they have a device that measures out a pint of blood like this: when the pint bag fills up, it's heavy enough to overcome the counterweight at the other end and the whole thing goes CLUNK, catching the attention of the staff.

-if the two COM's can be connected by a line that passes through the pivot axis, the behavior is similar to above, but less severe.

-if the two COM's can be connected by a line that passes below the pivot axis, the stable position will depend on the mass imbalance between the two ends. Remove a small amount of mass from the lower end, and the seesaw will resettle at a new angle, not necessarily thunking the other end all the way to the ground (unless you remove a lot of mass).

[SCSimmons]

Originally Posted by Irishman

How many times a day does the average person urinate? I say 8 ...

I say, what?

[Sapo]

Originally Posted by Irishman

How many times a day does the average person urinate? I say 8, so that gives
...
(I once puzzled myself and others how my weight could drop ~ 2 lbs within the course of about 4 hours one day - not exercising/sweating profusely, but working indoors in A/C. Finally figured out I had put coins in vending machines - a couple dollars worth. So no, I didn't pee that much. ;-) )

8 pisses a day is a lot. So are 2 lbs of change in a pocket (I am sure someone will come with a dollar amount shortly).

[Sapo]

Originally Posted by TruCelt

That's what I was thinking. But I doubt this is a link I want to click on from work. ;-)

How much movement is there?

I wouldn't say it is NSFW. It is a lot more humorous than it could be offensive. There is no anatomy shown at work, as it were.

[Sapo]

Originally Posted by ivn1188

Friction is a mechanical difficulty.

The answer to the thought experiment is "yes".

The answer to will this work in the real world is obviously "On which seesaw?". It will work on any seesaw that has less friction than it takes to resist about a pound (1 pint of water) pressing down at whatever distance the seat is from the fulcrum.

This is, in essence, my question. Is the seesaw where this could happen one that can be found in normal playgrounds (as opposed to a NASA lab)?

[Sapo]

Originally Posted by Evil Jon

Ask mythbusters, this is something they'd try.

This does sound like something they would try. Time to drop them a line, I guess. Is anyone here a regular at their board?

[Sapo]

Originally Posted by Joe Frickin Friday

It'll depend on exactly where the two centers of mass are with respect to the pivot axis:

-if the two COM's can be connected by a line that passes above the pivot axis, the system will be bistable: it will sit with one mass on the ground until a critical amount of mass is removed from that end, at which point it will tilt until the other end smacks the ground. When I donate blood at the local Red Cross place, they have a device that measures out a pint of blood like this: when the pint bag fills up, it's heavy enough to overcome the counterweight at the other end and the whole thing goes CLUNK, catching the attention of the staff.

-if the two COM's can be connected by a line that passes through the pivot axis, the behavior is similar to above, but less severe.

-if the two COM's can be connected by a line that passes below the pivot axis, the stable position will depend on the mass imbalance between the two ends. Remove a small amount of mass from the lower end, and the seesaw will resettle at a new angle, not necessarily thunking the other end all the way to the ground (unless you remove a lot of mass).

This post alone was worth the thread. I still want the answer, though.

[Irishman]

SCSimmons said:

8 pisses a day is a lot.

Really? That's once every 3 hours. If you piss less often, and still stay with the max 2L a day, then you piss more at a time.

Admittedly, I pee often, and I doubt there are a lot of pregnant women trying this experiment (not that I'm one of those), but I didn't think my numbers were way out of line.

So are 2 lbs of change in a pocket (I am sure someone will come with a dollar amount shortly).

Hmm, using weights from the US Mint site, I'm getting $20 in quarters (i.e. 80) or dimes (i.e. 200), or a little less than $10 in nickels (i.e. 40). This happened several years ago, so my memory is fuzzy, but things aren't quite adding up.

[brossa]

Originally Posted by Chronos

The real problem, I think, is that if it's close enough for peeing to make a difference, it'll also be close enough for small shifts in the person's position to also make a difference.

I agree with this; even if his feet don't move on the seesaw. Altering posture so that his weight moves from the toes/balls of his feet to his heels would produce a greater change in the torque on the pivot than would a weight loss of, say, a liter.

Let's see; a back of the envelope guesstimate with a 70kg guy who can shift his COG from 220 cm to 200 cm from the fulcrum without moving his feet will produce a change in torque 6.4 times greater than a guy at 220 cm who goes from 70 kg to 69 kg by peeing a liter.

This math may be totally wrong.

[SCSimmons]

Originally Posted by Irishman

Really? That's once every 3 hours. If you piss less often, and still stay with the max 2L a day, then you piss more at a time.

Admittedly, I pee often, and I doubt there are a lot of pregnant women trying this experiment (not that I'm one of those), but I didn't think my numbers were way out of line.

Actually, Sapo said that. I just implied it.
Also, it's once every three hours if you get up twice in the night to pee. It's every two hours if you manage to sleep through the night ... I'm taking a diuretic for high blood pressure, and I still don't pee that often. But I'm sure I do pee more than a cup at a time. Hell, sometimes I feel like Austin Powers waking up from a thirty-year deep freeze hibernation. (Wait, was that TMI?)

[Machine Elf]

Originally Posted by Sapo

This is, in essence, my question. Is the seesaw where this could happen one that can be found in normal playgrounds (as opposed to a NASA lab)?

OK, a plain ol' regular playground seesaw? What's the typical length for a playground seesaw at an elementary school, maybe ten feet from fulcrum to either end? This pic on Wikipedia look sabout right.

How much does the urine in one evacuation weight? 1 pint equals about half a liter, so 500 grams, so ~ 1 pound of urine. Unload one pound of urine from its location ten feet away from the pivot, and you've decreased the torque on that end of the seesaw by 1# x 10' = ten foot-pounds.

So the fundamental question is this: on a typical playground seesaw, is the friction torque on the pivot bearing typically less than 10 foot pounds? IMHO it's going to vary somewhat, but in most cases, I'd guess no. I think the typical seesaw pivot is just a short length of pipe riding on the exterior of a cross-bar (see pic at above link), and if you're lucky, it's not too rusty and maybe there's a bit of grease in there. That'll take more than 10 foot-pounds to get it moving.

[Baracus]

Originally Posted by Joe Frickin Friday

So the fundamental question is this: on a typical playground seesaw, is the friction torque on the pivot bearing typically less than 10 foot pounds? IMHO it's going to vary somewhat, but in most cases, I'd guess no. I think the typical seesaw pivot is just a short length of pipe riding on the exterior of a cross-bar (see pic at above link), and if you're lucky, it's not too rusty and maybe there's a bit of grease in there. That'll take more than 10 foot-pounds to get it moving.

In that case they could just add more counterweight. There is no reason why the counterweight has to exactly match the weight of the pisser. I don't really see why they couldn't get this to work. You just keep adding to the counterweight until the see-saw just tips over. Remove a half pound from the counterweight and let the urine flow.

[Sapo]

Thanks to those who have done some math. I have no tools to check your work but I have faith that if they were totally off someone would have jumped at them.

Originally Posted by Irishman

Hmm, using weights from the US Mint site, I'm getting $20 in quarters (i.e. 80) or dimes (i.e. 200), or a little less than $10 in nickels (i.e. 40). This happened several years ago, so my memory is fuzzy, but things aren't quite adding up.

Are those two rolls of quarters in your pocket our are you really really happy to see me?.

[Sapo]

Originally Posted by Joe Frickin Friday

So the fundamental question is this: on a typical playground seesaw, is the friction torque on the pivot bearing typically less than 10 foot pounds? IMHO it's going to vary somewhat, but in most cases, I'd guess no. I think the typical seesaw pivot is just a short length of pipe riding on the exterior of a cross-bar (see pic at above link), and if you're lucky, it's not too rusty and maybe there's a bit of grease in there. That'll take more than 10 foot-pounds to get it moving.

Does anyone have a ball park figure of the amount of torque it would take to move a playground seesaw?

[Chronos]

1 pint equals about half a liter, so 500 grams, so ~ 1 pound of urine.

Yet further proof that nobody actually understands the American system of units: You just had to convert into metric and back, using two approximations, to come up with the result that a pint of water weighs a pound, which is one of the design features of the system.

[garygnu]

A pint's a pound, but no longer the world around.

[friedo]

Originally Posted by Baracus

In that case they could just add more counterweight. There is no reason why the counterweight has to exactly match the weight of the pisser. I don't really see why they couldn't get this to work. You just keep adding to the counterweight until the see-saw just tips over. Remove a half pound from the counterweight and let the urine flow.

You're missing the point. Even if the pisser decreases his weight so he is a pound lighter than the counterweight, he still has to overcome the friction of the fulcrum to allow the see-saw to move. If the maximum weight one can lose in a single piss is one pound, and the torque friction on the fulcrum is greater than ten foot-pounds, then the see-saw will not move. (Assuming a ten-foot see-saw.)

You can overcome this by using a longer see-saw and/or one with a higher-quality bearing. Neither of which are likely to be found on an average playground.

[Baracus]

Originally Posted by friedo

You're missing the point. Even if the pisser decreases his weight so he is a pound lighter than the counterweight, he still has to overcome the friction of the fulcrum to allow the see-saw to move. If the maximum weight one can lose in a single piss is one pound, and the torque friction on the fulcrum is greater than ten foot-pounds, then the see-saw will not move. (Assuming a ten-foot see-saw.)

Let me see if I can say this more clearly. For sake of argument, say the static friction of our ten-foot see-saw requires 50 foot-pounds to get moving. Put 4.9 pounds more weight on the opposite end than what the pisser weighs so we have a net torque of 49 foot-pounds - the see-saw doesn't move. The pisser releases a pound of urine. Now there is a net torque of 59 foot-pounds and the see-saw moves.

[friedo]

OK, that makes sense.

[Machine Elf]

Originally Posted by Chronos

Yet further proof that nobody actually understands the American system of units: You just had to convert into metric and back, using two approximations, to come up with the result that a pint of water weighs a pound, which is one of the design features of the system.

Somewhere in the back of my mind I knew that 1 fluid ounce of water weighs 1 avoirdupois ounce, but I was much more acutely aware that 1 cc of water weighs one gram. So my immediate impulse was to come up with an SI quantity of water, then an SI mass, and convert back to avdp. And whaddya know, it was suspiciously close to a pound of water; I just wasn't suspicious enough.

[Fastidiots]

Piss.

For the sake of art, I'd say this guy could probably pack 800g of fluid, and go in search of the nicest and newest see-saw he could find.

I say entirely possible.

[Sapo]

Originally Posted by Baracus

Let me see if I can say this more clearly. For sake of argument, say the static friction of our ten-foot see-saw requires 50 foot-pounds to get moving. Put 4.9 pounds more weight on the opposite end than what the pisser weighs so we have a net torque of 49 foot-pounds - the see-saw doesn't move. The pisser releases a pound of urine. Now there is a net torque of 59 foot-pounds and the see-saw moves.

So the friction doesn't really matter as long as you do your homework and account for it. Right?

[TimeWinder]

Originally Posted by Chronos

Yet further proof that nobody actually understands the American system of units: You just had to convert into metric and back, using two approximations, to come up with the result that a pint of water weighs a pound, which is one of the design features of the system.

I'd say that's pretty much the only design feature of the system, and as is typical for such a cobbled-together unit, we even got it wrong. A (US) pint of water weighs 16.69 ounces, more than two thirds of an ounce more than the design spec.

[Morgenstern]

Maybe if you added a good crap the see saw would respond. My experiments show that a crap eliminates .8 to 1.5 pounds. I weighed in when I was in a weigh loss program. A good crap and a pee before weighing was worth 1.5 to 2 pounds on a very sensitive scale.

[USCDiver]

One thing to consider with this particular picture (hopefully I didn't skim over someone else making the same point) is that the fellow in question is not done peeing yet. He clearly has a good stream still going in the After photo. So if this were a carefully balanced situation it will have to be closer than just full vs empty bladder.