This is one of those questions where the answer has never made sense to me. We're supposed to drink all this water. I remember the old days before weigh in at Weight Watchers (which met at lunch time) I wouldn't eat or drink all morning before the weigh in. Here's why...

A gallon of water weighs approximately 8 pounds (8.34 to be exact) and a pint (which is 8oz) of water weighs 1.04375 pounds. So don't you GAIN a pound every time you drink a glass of water? And we're supposed to drink 8 glasses a day?

I realize there are no calories, but WHERE does the WEIGHT go?:think

You have to keep in mind that we're constantly losing Water, constantly, and 2 liters a day may not even be enough to replace what's being lost.

Most adults lose between 2.5 and 3 liters of water per day. Urination/defication, sweating, breathing... all remove fluids from your body (jsut breathing causes a loss of about 1 liter per day - add extra for heavier breathing, deep breathing, etc).

So if by "where does the weight go" you're asking where the Fluid goes -- it's absorbed. You're roughly 60% water, so you're just replacing -- you.

you pee about as much as you take in because it is constantly recycled. ever notice if you only drink one or two glasses of water you only pee maybe twice or three times that day? But if you drink a lot then you pee a lot. it just gets recycled. People who are proud of their "water weight" being lost, are unknowingly proud that they are dehydrating themselves. LOL

Not to be gross, but I drink a LOT, and not that much comes back out in the bathroom. I must spit a lot when I talk! LOL

I also can't figure out why a fly doesn't hit the roof of an elevator when it flies in the door just before it goes down, or doesn't smash into the windshield if it flies in a car window at 30 miles an hour.

Hubby will like the idea of some more 'heavy breathing' !

Now you are just making my head hurt. LOL

I also can't figure out why a fly doesn't hit the roof of an elevator when it flies in the door just before it goes down

Because the fly is not affected by the elevator's movement/intertia. If it's a dumb fly that doesn't realize the roof of the elevator is coming quickly, it will smash. Otherwise it's no different than you standing outside of an elevator, sticking your hand in, and wondering why your hand doesn't drop as the elevator drops.

, or doesn't smash into the windshield if it flies in a car window at 30 miles an hour.

Because there's a cushion of air flowing around the car, that the fly "glides" on - like a Water slide. Unless it's a big ass fly, then has more velocity than the cushion does resistance, and *splat*.

Ok, I know you weren't really looking for answers, but I'm bored and a :nerd: who's married to a physics :nerd:.

Now I know everything I ever wandered about flies and peeing. I have laughed my tail off. You guys are hilarious. LOL

I live in TEXAS and the flies are much larger down here! LOL!

The sticking the hand in the elevator theory doesn't work, cause your feet are still stuck to the floor outside the elevator. The fly didn't change weight when he flew into the elevator.. so unless he is flying 'down'; logic would dictate that he hit the roof... right?

Or the other option you propose is that the fly has 'conscious' thought and that he flew into the elevator because it's easier than flying up the stairs?? :think hmmm....

A fly doesn't hit the back of the windshield because it does not have enough mass to carry momentum through the surrounding air, which is traveling at the same speed as the car - so it quickly adjusts to the speed of the air around it. Just like if a feather blew in the window it would not fly all the way back to the back window. Plus the fly can adjust its own speed in addition to having the advantage of small mass.

Similar to how far can you throw a light object vs a heavy object??

Momentum can be thought of as mass times velocity. People being heavy will have lots of momentum whilst the fly and the air will have little. The fly or an air particle will therefore have insufficient momentum to force themselves through the surrounding air particles. A person having lots of momentum would easily punch through the surrounding air and carry on to the back window and SPLAT!

The sticking the hand in the elevator theory doesn't work, cause your feet are still stuck to the floor outside the elevator. The fly didn't change weight when he flew into the elevator.. so unless he is flying 'down'; logic would dictate that he hit the roof... right?

EEk, ok -- will do my best to avoid getting deep into it, the lingo, etc. This may cause me to omit scientific detail in favor of getting the "point across", but so be it. :confused:

Short answer - Nope, and it is the same thing (metaphorically speaking).

When you're in the elevator, your feet are on the elevator floor. When the floor drops, you drop (gravity) because the elevator floor is no longer exerting pressure/resistance on you. The fly is not on the elevator floor, he is just occupying space in the elevator. Just as your hand is not on the elevator floor, it is just occupying space in the elevator.

If the fact that your feet are on the ground outside the elevator is tripping you up, then imagine you can float, and you're floating outside the elevator, and stick your hand in the elevator. Your hand still doesn't move.

Picture a fly hovering inside of a big glass tube. The fly is still - staying in the same spot, right? So let's assume that's all the fly can do, it can't fly to the left or right, it can only hover (trust me, that will make this MUCH easier to understand). If you grab the tube and shake it vigorously, the fly isn't going to start shaking too, it's going to stay in the same spot, and the tube is going to move around it. HOWEVER, if you have a dead fly that can't over, and is laying on the bottom of the tube, it will start shaking because its movements are no longer independent of the movement of the glass (skip long explanation about why something inside of something else moves when the outside piece is moved).

Lots of people get the same principle confused, and think that if they're in a plummeting elevator, all they have to do is jump right before impact and they'll be fine. And now they're dead. They're moving at the same speed as the elevator. The fly is not because it is only occupying space within the elevator, it is not moving with the elevator, it is moving independent of the elevator.

Enter relativity. The fly's position will lower when the elevator drops, but only relative to where the elevator was before. If you're outside look inside at the fly, and the elevator goes down 3", the fly will still be in the same place as you look at it. But relative to the people in the elevator, the fly is 3" higher than where it was.

Here's another way to look at it:

If you're standing in the back of a truck that's moving down the highway, and you throw a ball into the air (assuming a vaccuum), the ball will come back down in the bed of the truck. The only reason it doesn't come down in the bed of the truck "in the real world" is because while it's in the air, the moving air exerts force on it and slows it down/pushes it, so it ends up outside of the truck bed. In a vaccuum the ball would land in the bed of the truck because it's moving at the same velocity as the truck is, you are, etc. When you throw it up, it still carries the momentum even though it's temporarily "detached" from the truck.

If you're driving the truck with the windows rolled up, air conditioning off, etc. and there's a fly in the cabin and you apply the brakes sharply, the fly doesn't go flying into the windshield, it keeps buzzing around your head. Same principle as the elevator.

If you think this is hard to wrap your head around, try listening to some of the quantum stuff my husband rambles on about... the physics around black holes, time travel, etc. I can keep up iwth him most of the time, but sometimes all I can do is there and watch his dust as he flies right over my head. His latest kick is string theory - also called The Theory of Everything as it "it attempts to provide a complete, unified, and consistent description of the fundamental structure of our universe." He gets going on that stuff, and I just start flipping the channels. :confused:

donali and Wheetsin,

My head hurts the same way as when hubby tries to explain it. He's the hard core science type also. Usually when he gets started, my eyes kinda glaze over and I start nodding my head. :confused: We've had the fly & elevator discussion many times - I think I about have him convinced it will hit the ceiling! LOL!

Your descriptions make sense (especially the dead fly in a test tube), but that little part of my mind is also asking hubby while we're flying where the 'magic' went when the plane does an unexpected 'bobble' (my term, not his).

Water weighs 2.2# per quart.

Nm123456789

the weight of water is about 10#/gallon., This is based on a 10 gallon fish tank weighing approximately 100# heavier filled than unfilled. I am totally trusting the fish experts who told me this so take it with a grain of salt :tea:

Okay, this is easier to understand if you think of the air as something thick with mass, like Jello. If a fly is suspended in jello (which fills the elevator) it will move up and down with the elevator without changing position, because it is too light to move through the jello on its own.

Suspend something heavier in the jello, like a marble, and if there is enough speed in the elevator going down, and enough of a sudden stop, the marble will move through the jello and end up on the bottom at that sudden stop.

So to a fly, air is more like the consistency of jello than it is to us. Just like we would be hard put to make our way through thick mucky mud, but to an elephant it's nothing.

And glass is a liquid... Seriously...