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Pop Quiz #2 - Freezing Water - High School Physics Revisited(36 posts)

Pop Quiz #2 - Freezing Water - High School Physics Revisitedjose_Tex_mex
Jul 2, 2002 6:42 PM
All,
Since we all did so well on the last quiz I thought I would post another question and this time provide the Gold Star (maybe mustard) for you to post via the honor system on your fridge.

Actually, I just wanted to lighten the mood of this board heading into the 4th of July Holiday.

Anyhow, here's the question. It's quite a famous one, I think Bernoulli came up with it:

You put two wooden buckets of water outside on a freezing day. There are no lids on either bucket. Bucket A has nearly boiling water whereas Bucket B has an equal amount of colder water (let's say 50 C). Which freezes first? As always please provide your rationale, even if it is "I am drunk and therefore it is..."

Extra Credit: What would the result be if we used steel buckets?
I cheatedDougSloan
Jul 3, 2002 5:50 AM
I cheated and found the answer (or was this "open book"?). You can find the answer to anything on the internet.

The answer is counterintuitive, for certain. I was amazed. I won't spoil the fun, though.

Doug
Extra creditmr_spin
Jul 3, 2002 6:23 AM
Which bucket will produce clearer ice?
Use distilled waterjose_Tex_mex
Jul 3, 2002 7:45 AM
I am not sure if the urban legends I have heard are true. However, I thought clear ice came from using distilled water and the way it was formed - in layers like in the restaurants.

With that said, hot water comes from your boiler where it has been sitting around getting hot. It's different from the cold water which is why you do not use it to make tea - it wouldn't taste right.

Gases including CO2 N2 and O2 are less soluble in cold water than warm water; therefore as part of the cooling and freezing process, millions of tiny gas bubbles are formed in the ice as the gases come out of solution. These cause distortion due to refraction. Burning them off at higer temps might cause a clearer ice cube.

Thus, if I had to take my pick I would go with the hotter water making clearer ice cubes. But I do not think that is correct as restaurants do not use this technique and neither do icicles.

Do I get the gold star?
yesmr_spin
Jul 3, 2002 7:57 AM
Your explanation is accurate. Basically you boil the air of the water, resulting in clearer ice cubes.
No Credit:Which way does the water spin down YOUR toilet? Why?nm128
Jul 3, 2002 6:28 AM
Depends on which hemisphere you are in...nova
Jul 3, 2002 6:43 AM
Hopefully we all remember that from high school. If not, this topic was covered on an episode of The Simpsons, so there is no excuse for not knowing it!
Only if your toilet bowl is a few hundred miles in diameterjose_Tex_mex
Jul 3, 2002 7:31 AM
The direction of the swirl in your toilet is dependent upon the dynamics of the jets therein. It is a common misconception that the coriolis force causes different swirls depending on which hemisphere you are in. In fact coriolis effect is far outweighed by the effects of small initial fluid vortices and wind (No pun intended) over the top of the bowl.
If your toilet bowl were a few hundred miles in diameter, then the Coriolis force of the rotating Earth would easily overcome the random water currents and force the bowl to empty its contents in a counterclockwise swirl. If you had Southern Hemisphere friends with an equally large toilet, then theirs would indeed empty in the opposite (clockwise) direction.
and deep too.....nm128
Jul 3, 2002 7:58 AM
Let's Drain Some Pools!!!jose_Tex_mex
Jul 3, 2002 8:31 AM
I wonder if we were to drain Olympic size pools in both hemispheres if we might get the effect? Physics wise the differnce isn't much - but it feels big!
I disagree. . . real life observationsMike P
Jul 3, 2002 8:56 AM
While I was in the military, I had the wonderful experience of being stationed on a submarine for a while.

In the Northern hemisphere, the water always flowed down the drain in a counter-clockwise rotation. When we went south of the equater, the water flushed clockwise. Same plumbing, same toilets (we called them shitters). The bowls were of a normal size and as such were much less than a few hundred miles in diameter. This is more easily observed by filling a sink, then pulling the drain plug.

The shitters were, however, made of metal, so I guess if they were to freeze, it would take longer to freeze than hot water in a wooden bucket. And the ice would be less clear. In either case, I wouldn't put the ice in my tea.

Mike
At the equator?bikedodger
Jul 3, 2002 11:49 AM
So, at the equator, did the water just stay in the toilet as it did not know which way to go? Or did half go clockwise and half counter clockwise?
Nah, if your theory were correct..nova
Jul 4, 2002 9:10 AM
If your theory were correct, then the water would swirl in different directions down my tub drain each time I drain it. Statistically, it would swirl 50% clockwise, and 50% counterclockwise.

That doesn't happen - it ALWAYS swirls in the same dirction. I'm 36, and I've been taking baths in the northern hemisphere for a long time.
If so Coriolis is greater than gravity, but I can't feel it...jose_Tex_mex
Jul 4, 2002 8:01 PM
Nova,

My point is that there's many more factors which influence the swirl of drainage than the Coriolis. Simply put, the different swirls being due to the Coriolis is an urban legend.

Your tub was not designed with science experimentation in mind, or maybe it was. Tubs are made to drain and thus channel water in a given direction. Is your tub 100% level width wise and length wise? Is your tub 100% symmetric? Is the surface area of your tub 100% consistent and smooth or might it cause turbulence.

When you drain the water on your tub is it still moving? How many hours did you allow the water to stand to ensure there was not motion due to your being in it or its filling?

Is the tub and water kept at thermal equillibrium. If the water is not 100% uniform temp (and with the tub) then there will be currents. Can't have currents if it's all about Coriolis.

Statistically, I did not say it was random so I doubt it would be 50/50. There are factors which influence its swirl. The Coriolis Force is not a major contributor. Probably less than 1/billionth of gravity.

Don't take my word for it do a google search and see what the Physics sites say.

Coriolis is a macro event. There are SOOOOO many more factors contibuting SOOOOO much more to the drain.

Again, this is one of those popular urban legends.

Think about it. If the Coriolis Force was soooo strong that it could overcome gravity and swirl the water it would be as trivial to show as gravity. Try proving the Coriolis force exists. Better yet, search on-line for those who have using micro events - it's not quite easy.

This would have been a good Pop Quiz #3.
yes, however...nova
Jul 5, 2002 4:16 AM
All good points, and I'm not a physics wonk as you appear to be (that wasn't an insult!)

How many tubs and sinks have I used in 36 years, all over the world? (Northern hemisphere, anyway) I have no idea. But it is an awful lot.

When a tub or sink is plugged to retain water, and then the stoppage is removed to allow drainage, it ALWAYS rotates the same way. ALWAYS! So what's up with that? They are all unlevel in the same fashion? They are all designed to swirl the water in one direction? No way.

Perhaps a better question would be, why doesn't the water drain "straight" down, on at least SOME of these bathroom fixtures?

And how do you explain the submariner's observations in the post above?
And besides....nova
Jul 5, 2002 4:20 AM
If all sinks in the USA are designed to swirl water clockwise (or are all deliberately unlevel and thus ALL produce said rotation), you can rest assured that the French would design their sinks to do the opposite of whatever is happening in US sinks.

(consider NTSC v. SEACAM television formats...)
straight dopeDougSloan
Jul 5, 2002 6:17 AM
http://www.straightdope.com/classics/a1_161.html

http://www.gi.alaska.edu/ScienceForum/ASF2/221.html

http://www.bnl.gov/scied/contests/maglev/mste/res/spin.html
just filled a sink several times...nova
Jul 5, 2002 8:38 AM
and the draining water spun counter-clockwise every time.

The sink is not manufactured with little sluices to make the water spin that way.

Perhaps it isn't level. Perhaps the motion of the water just sets things up so that when it drains, it spins counterclockwise.

My point is that after 36 years of draining sinks and tubs, I do not recall ever seeing water drain in a clockwise direction. Of course, I may have seen such an event and just don't remember it. But if I ever DO see it, I'll be sure to post it here :)

Also, there is such a thing as statistical probability. If all the factors cited by Jose and the websites really have a truly randomizing effect on the direction of the spiral, why don't we see more of a 50/50 split (clockwise to counterclockwise?)

Those "randomizing" factors produce statistically predicable results over 99% of the time. So they aren't randomizing after all.... Consider the question in the context of probability (an area of mathematical study unto itself) and the physics side of things do not provide an accurate answer.

I think the physicists need to consult with the mathematicians to figure this out.
quantified versus qualifiednova
Jul 5, 2002 9:05 AM
Direction of water spiral (observed): 100% Quantifiable. Water spiral is nearly ALWAYS (to my knowledge) reported to be in the same direction depending upon hemisphere, regardless of whether or not this is an urban legend.

Level-ness of fixture (sink or tub) on all planes: Completely unquantifiable given the test environment of every sink & tub in the world.

Motion of water in fixture: non-quantifiable in the vast majority of observations (trillions of "drainage events" in the US alone)

Maybe my bloodsugar is too low to understand (it's lunchtime) but if you start looking at the measurable results, the water -prefers- to spin in just one direction.
ignoring the scientists?DougSloan
Jul 5, 2002 9:39 AM
Did you guys read the scientific findings on this? One sink isn't a good test. Do lots of sinks, bath tubs, etc., and use the same methodology, that is, empty right away or wait 24 hours.

For some reason, I accept their findings more readily than any of our reasoning or anecdotal observations.

Doug
math v physics, again.nova
Jul 5, 2002 11:42 AM
sure - everything they say makes sense in the context of what they are saying. Jose said that he wasn't talking about statistical results. He can't, otherwise the position he takes wouldn't hold water. (pardon the pun)

But the fact is: you consider this an urban legend because it is a near universal observation. People think this because they see it. That means it is quantifiable. Something is true if it is quantifiable in the affirmative. So why does everyone see water rotating one way down a drain? OK, I accept that it isn't due to the Coralis effect. So tell me why it DOES rotate one way down a drain over 99% of the time for over 99% of the eyeballs watching it?

Math is the only true universal language. It is unconstrained. Physics is constrainted by human perspective. And that is one MAJOR constraint.

Remember, the most educated and advanced minds in human history have at times:

Thought that the Earth was flat
Thought that draining your blood would prevent disease
Thought that bathing would cause disease

And this stuff was in *writing*... which of course made it true for everyone who read it...
Cock a doodle doo - and the sun rises!!!jose_Tex_mex
Jul 5, 2002 1:33 PM
Nova,
You asked for the Physicists to talk to the Mathematicians well, I have degrees in both Physics and Math - what luck!

(Me Being ficitious)
Every morning the rooster across the street crows and the sun comes up. This happens EVERY morning for my ENTIRE life. Do we therefore conclude that the effect of the rooster crowing is the sun rising? Hope that rooster never dies!

Also, you're killing me wrt "Physics is constrainted by human perspective." That just hurts. Them are fighting words!!! Physics is more like math in words. Remember, Newton invented Calculus in order to derive his laws of motion. One of the reasons I post these Pop Quizes is to show via Physics how wrong our perceptions can be. Math doesn't do a lot until a Chemist, Physicist, Biologist, or other "ist" gets a hold of it.

There are a lot of real life phenomena I can explain by using high level Mathematics and Physics. The problem is that not many others can understand them. When asking for proof of such an event one must keep this in mind.

A few points:
1) No-one ever said the event was random. It is influenced by factors. A major one not being Coriolis. These factors effect the drain and cause the result.

2) WRT Statistical Methods. If you flip a fair coin 1 million times you would expect to see a bell shaped distribution whose first standard deviation coincides with a point of inflection, blah, blah, blah... HOWEVER, I could flip the coin 1 million times and get all heads or all tails.

4)The urban legend is that the swirl is caused by Coriolis. I not mean to imply the swirl going in any direction was an urban legend.

5) Not everyone sees the same motion. That's a statment you cannot make. You could do a random sampling of the population and make an inference upon a sufficiently large number of respondants... Studies show that a significant number of people... You might want to post this as a thread and see if we can get some people from down under to reply.

6) As for your sink - glad you using experimentation! Try putting a marble in the sink and see if it moves. However, did you take into account all of the constraints mentioned in my prior posting?

This is an extremely difficult problem to solve (as it's real life) and goes mostly to thermodynamics and fluid dynamics. You'll also want to be up on your partial diff eq's.

With that said, let's try to see why the swirl goes in one direction. I suspect that the most influential factors are:
1) The motion of the water prior to drainage.
2) The shape of the pipes draining.
3) The dynamcis of "pulling the plug.
4) The dynamics of the draining fluid.

A few factors to consider:
1) There aren't many manufacturers for bathroom whitewares. I imagine their designs intuitively display a consistent characteristic makeup. The marble test I just did in the bathroom tub went to the right of my drain and circled CC - just like the water. I would conclude the shape of my tub caused this.

2) Drain Vortices. Because of friction the water just does not "fall" straight down out of the tub drain. When water goes from a wide area to a narrower it speeds up. Thus, you have a vacuum effect in that the escaping water pulls the tub water. Due to friction the pull is not even and will probably follow the path of least resistance. The resulting effect is the development of a swirl.

3) Most drains have similar pipes underneath them - like the u-shaped pipe under the sink. This shape will have some say on the escape of the water and thus on the drain.

HERE's an experiment. Fill up the sink cause a little swirl in the opposite direction by stirring. Does the swirl continue or is it counteracted?

Talk to you soon - gotta barbeque to go to. Hope you're doing the same...

Best of Luck
no bbq, but a ride is in store this eveningnova
Jul 5, 2002 2:06 PM
Thanks for the essay! Actually, I'm not "killing you", you are allowing me to "kill you". Now we are in the realm of psychology...

Manufacturers of most fixtures likely do not design their products with a "ramp" or sluices to get the water to spin a certain way. What if it is installed in an uneven fashion? (As they all likely are... ) then it would defeat the design, and waste money in the fabrication process.

Yep, agree on the drain vortices you describe.

Nope, most drains do NOT have similar pipes under them, you are being North-American centric. Hell, I've been to a fairly modern building in Germany where the toilet is literally a hole in the floor. (extreme, irrelevant example, but then so is your coin-toss example)

And yes, if I spin the water clockwise, it will evenutally counter-rotate and finish draining counter-clockwise.

Statistical sampling, in my opinion, would reveal that most casual observations of most people would result in the same quantifiable result. As a mathemetician, you know that you could flip a coin 1M times and get heads each time, but you also know that it isn't going to happen. It is like saying give 1000 monkeys 1000 years in front of 1000 typewriters, and they will produce the combined works of the Bard.

Good luck to you! I look forward to your groundbreaking discoveries in the world of academia/physics! Glad I could give you something to look down upon, it obviously gave you an ego boost! :)
HA!DougSloan
Jul 5, 2002 3:57 PM
I just did an experient. I have a bathroom with two identical sinks. I filled them both to the top, then let them sit a minute. Then, I unstopped them simultaneously. ONE SWIRLED CLOCKWISE, AND ONE COUNTERCLOCKWISE!

These are(ostensibly) identical sinks.

So, what does that prove?

Doug
Thank younova
Jul 5, 2002 4:36 PM
And thus, the myth is fully dispelled for me. (provided you are telling the truth, which I think you are :)

You may have proved my point that sinks are not likely to be fabricated to force water to swirl in one direction or another. Really, what would be the point from the manufacturer's point of view? (Toilets, yes. Sinks and tubs, no.)

I'd attribute the different swirls to the vacuum formed by the vortex...
or the equator runs through your bathroom! :^P (nm)nova
Jul 5, 2002 4:38 PM
x
Misspelled Facetiousjose_Tex_mex
Jul 6, 2002 2:01 PM
Sorry I offended you. I thought by saying "(Me Being Ficitious)" explained that what was said should be taken lightly - I even spelled Facetious wrong.
- Won't bother you again with "essays" or "academia."
Again, I apologize.
Answer Timejose_Tex_mex
Jul 3, 2002 8:28 AM
Hi Class,
Here's the answer, I hope. There could be some discrepancy here as results can also depend upon the initial volumes of water and the shape of the buckets.

As for the quiz being open book - not a problem. I always love to hear the answers in someone else's words. Better yet, in case I am wrong, it's nice to have a heads-up. Award yourself the gold star and where it proudly this 4th of July weekend explaining to everyone how you achieved it!

Aside: I am sure by now we are learning to go against intuition.

Ans: "Bucket A" with the near boiling water freezes first. Here's why...

Doesn't sound right does it? There's only one cooling curve for water based on time vs temperature. Hmmmm.

First of all we are dealing with buckets made out of wood - a lousy conductor. Heat will be lost basically by two methods: partly Newtonian and partly by evaporation of the contents. Because the buckets are made out of wood with no lids evaporation will play a much more important role.

When temperatures are high, most of the heat loss will be via evaporation. As the contents of the hotter bucket evaporate Bucket A undergoes a loss of mass much greater than that of Bucket B. The more evaporation that occurs the less mass there is to be cooled.

Remember water is difficult to heat and/or cool. Thus, over time Bucket A is able to make up for its positioning on the time cooling curve by having to cool less mass.

Experiments have shown a wooden bucket of water starting at 100C would finish freezing in 90% of the time taken by an equal volume starting at room temperature.

Kudos to our ancestors using wooden pails and buckets who noticed this.

As for the extra credit problem, now we have very good conductors - steel. Considerable heat is transferred through the sides of metal pails, and evaporation no longer dominates the cooling, so in this case intuition prevails and the cooler Bucket B wins the race!

Lesson Learned Here: Physics postings are much more fun than Political. I think I'll stick to the Physics.
websiteDougSloan
Jul 3, 2002 8:31 AM
http://victoria.tc.ca/science/information/science/physics/physics11.13.html

Good question. I never would have thunk it. I enjoy those physics questions that are totally counter-intuitive. I'd bet there are many in the bicycling realm that we take as dogma that are untrue, too. Anyone know of any?

Doug
Steer in the direction of the fall in order to not fall.jose_Tex_mex
Jul 3, 2002 8:53 AM
Glad you enjoyed that one. I think I remember it from a Thermo class where we were talking about how incredible water is.

WRT Bicycling, I do not know the entire specifics of the Physics involved. However, one counter-intuitive thought is that when you are falling one needs to turn in the direction of the fall in order to return upright. We do this all day long when we steer. If we could not steer the bike would be un-rideable.
that's a good oneDougSloan
Jul 3, 2002 9:10 AM
Same thing about overlapping wheels -- steer into the other rider.

Countersteer.

Aluminum is harsh (when it's much softer than other frame materials).
Here is what I got out of this threadnova
Jul 5, 2002 4:19 PM
These are interesting questions. You personally know that there are myths and misconceptions about things like why water swirls the way it does down a drain.

You are kinda/sorta looking down your nose at people who buy into the myths, while at the same time trying to dispell the myths.

Here is the rub: you are also kinda/sorta looking down your nose at people who don't accept what you have to say as being the end-all on the discussion. A little bit of hipocrasy is always entertaining... :)

You strike me as someone who is a student or works in academia (?) It may surprise you to learn that I have an MS in a Telecom, but I wouldn't look down my sniffer at someone who couldn't tell me how Nyquist's Theorem might apply to how RBR is being brought to them at their desktops... or discuss the relative disadvantages and merits of fixed verus variable payload sizes in cells and frames. (And trust me, electrically-formatted cells and/or frames skitting across a wire are allowing you to read this right now) Heck, odds are that I may have played a role in developing the technology which is allowing you to read this message.

But I'm no better or worse than the guy who is scrubbing sinks and toilets right now on the 17th floor of 277 Park Ave, and has no clue as to why the water is swirling one way or another and couldn't tell me that 'modem' is an abbreviation for Modulator/Demodulator.

Your dismissive nature of someone who questions your postings says something about your scientific detachment. Someone else wrote to me "Do you really not beleive the scientists?" Well, Extreme Example: Nazi Germany had Scientists. (I said it was an extreme example! but it illustrates a point)

So - higher education is about creative thinking. Being creative involves asking questions, and not accepting things by rote. And it is good that you are educated. But if you don't question the things that people tell you, especially on this board (!) what are you thinking!? (and I had the sheer audacity to question *you* - eegad, I must be a dolt!)

Sooner or later, discussions on this board tend to lapse into who has a better education, who has more money, blah blah blah. It is actually kind of disgusting. Bottom line: if you think you know it all, you don't know much.
Making Tea? Don't Use the Hot Water! - Another Question?jose_Tex_mex
Jul 3, 2002 8:40 AM
When I was young and my parents asked me to put on the kettle for tea I always used the hot water. My rationale was that it took less time to boil - I was right. Impatient youth.

However, parents and grandparents could always tell I used the hot water and complained of the taste.

I did not realize that we weren't just drinking H20 but dissolved gasses et al. Remember, H20 is colorless, odorless, and Tasteless. We can cerainly taste water (ever drink real H20?). The problem was that the hot water came from the boiler where it had been sitting probably for hours degassing - de-tasting.

Needless to say I use cold water today as it tastes better. However, now I have to wonder why this is. Both the hot and cold water need to reach the boiling point before we make tea. Do not both applications of heat de-gas the water? Or, is there a minimum amount of time the temperature must be held to de-gas the water? That is, perhpas, the relatively short boil time of the tea has a role to play.

Perhaps, boilers are just nasty places for tasty water to be.

Any ideas?
hot water=sediment from hot water heater (nm)JS Haiku Shop
Jul 3, 2002 10:04 AM
will this be on the test?128
Jul 3, 2002 9:38 AM
so, are we basically saying that less water by mass will freeze faster than a greater mass of water? Because we've lost water to evaporation in certain containers? That actually seems intuitive, once you get past the mass issue. I was hoping for something a little more sexy. Science is....a let down!

Tried this experiment once in the freezer with the usual plastic ice trays: cold water froze first. Margarita; second.
nmjose_Tex_mex
Jul 18, 2002 8:49 PM