Fact or fiction?????????

Well way back when I was in school they always told us the water would freeze faster if it was hot. So which is it does hot water freeze faster then cold??? Also back up why your answer is the correct one. Been thinking about setting some water out but it is to cold and I'm to lazy plus watching water freeze might get boring LOL

I read it somewhere that a specific amount of water loses heat at the same rate whether it's hot or cold, in a place of the same temperature. Therefore, the colder bucket of the two would freeze first.
Probably first questioned by a guy who fell asleep in the bathtub on a cold winter's night. It just seemed that it cooled off a lot faster because when he woke up, he was already cold....

Colder.I never questioned what I was told about this subject.

Vito

Are you kidding me? Thats like asking what weighs more; a ton of bricks or a ton of feathers.lol. Seriously though the hotter the water the longer it takes to get down to 32 F.

fiction, place a ice tray of each in the freezer and see which one freezes first. I could be wrong, what I do know is cold is not made, the heat is just removed.

(quoted from post at 23:45:40 12/27/09) Well way back when I was in school they always told us the water would freeze faster if it was hot. So which is it does hot water freeze faster then cold??? Also back up why your answer is the correct one. Been thinking about setting some water out but it is to cold and I'm to lazy plus watching water freeze might get boring LOL

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Why not just put two containers of water in your freezer and see for yourself?
I think this misconception originates from hot water lines freezing before cold lines. This is true because of material fatigue. The hot line has been heated and cooled many times and is therfore weaker.

That was one of the experments we had to do back in school and the kids that said hot was proven wrong

(quoted from post at 18:45:40 12/27/09) Well way back when I was in school they always told us the water would freeze faster if it was hot. So which is it does hot water freeze faster then cold??? Also back up why your answer is the correct one. Been thinking about setting some water out but it is to cold and I'm to lazy plus watching water freeze might get boring LOL

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our uncontrolled experiment would be worthless, because in heating the water you will alter the air content, alter impurities, etc., thus making the comparison invalid. Heat will transfer to the surrounding cold air at a greater rate from the hotter water, initially, than from the cooler water, BUT, once both reach the same temperature, thereafter, the rate from that temperature to freezing will be the same, IF both samples have same air & impurities content, control of evaporation and a number of tiny variables. The problem is that control of all these variables is so difficult that you can under differing circumstance find either one to freeze faster from time to time. So, bottom line for Joe Blow, is yes & no.
You didn't really expect a definitive answer, did you? After all this question is about as old as 'which came first, the chicken or the egg?'

Yes, you were told correct in school, warmer water WILL freeze faster. The warmer water has less mass and less disolved gas. My daughter won her high school science project with this. Her dad has a degree in the physical sciences and he would not steer her, or anyone else, wrong on this.

Water that has been boiled and at the same temp as the unboiled water will freeze faster.

If the water has been boiled its water vapor and no longer in the pot to do anything with

Under certain conditions, hot water will freeze before cold.That has been known for thousands of years. Noboby yet as proven WHY it happens. Personally, I've seen it happen many times when fixing plumbing in houses with unheated crawl spaces. Most of the time, the hot water pipes freeze first, not the cold water pipes.

One situation where some people have tried to explain it is with the "Mpemba Effect."

It has been proven to happen over and over by scientists, but "why" it happens is still theory.

The latest theory I've heard about is the following:

"Now Jonathan Katz, a physicist at Washington University in St. Louis, has come up with a new hypothesis. Katz's explanation hinges on the presence of solutes. or dissolved substances, in water. "Hard" water contains more solutes than "soft" water does "

Not the same or even close to the question which weights more a ton of feather or a ton of bricks because a ton is a ton. Now if you said a ton of gold or a ton of feathers well then believe it or not a ton of feathers weights more then a ton of gold

ROFL!

Back in 5th grade, our teacher stated hot water would freeze quicker than cold water due to the molecules being more sparcely distributed. My father disbelieved me, and we spent the night checking the freezer, the hot froze first.

Im not sure about that question but I do know that tap water will boil quicker in the microwave than purified water. Purified water will even explode in your face if you get it too near the boiling temperature ( 212) and happen to place a foriegn object like a spoon in it.

The mass will have little to do with it. A gram of water is a gram of water.

My high school physics teacher threw a knuckleball into an extra credit question on an exam once.

Take a 500 gram snowball of uniform temperature of -5*C. Throw it at a wall. How fast does it have to be going to melt completely on impact?

The red herring was the mass. It made no difference. Each gram/mole/molecule of water requires the same amount of energy to warm to the melting point. Similarly, each unit of mass of the water needs to transfer sufficient energy out to freeze.

It has to do with the amount of impurities in the water. Water which has been heated tends to have less dissolved gas, particularly chlorine if you have city water. With less dissolved gas or other impurities, the water will freeze at a slightly higher temperature. That's why salt is used to melt ice...a strong salt solution may not freeze until somewhere below 0.

Therefore, water which has been heated will typically freeze at a slightly higher temperature than water from the same source which has not been heated.

Try this will distilled water, and I'll bet the cold water will start to freeze first, simply because the hot water has to cool off before it can start to freeze.

Never ceases to amaze me what sort of nonsense & mis-information people like teachers can come up with.

Keith

Warm water has less mass per volume. Steam is an extream, but revelant example. If, everything else equal, you start out with a cup of water at 210 F and anouther at 50 F the warmer water will freeze quicker and you will have a smaller ice cube. I can not imagine how throwing a showball compares. However if you were to throw a snowball at several times the speed of sound friction forces would cause it to melt rather quickly.

They relate because the freezing of the water or the melting of the snowball are both a matter of transferring energy.

And yes, in our post-mortem of that exam, those who did not see past the red herring brought up the friction factor, as I recall the correct speed was right up there. The teacher reminded us that this was high school physics. And now I think of it, he worded the question so that the mass of the snowball was 500g at the moment it hit the wall, taking out the friction factor. But it would have made no difference, either, how densely the snowball was packed. A gram of water is a gram of water.

Nothing was said about "boiling"! I suppose you are going to tell me if you place a cup of 150 degree water beside a cup of 35 degree water in the same freezer that all that heat in that 150 cup will be depleted down to 32 degrees faster than the 35 cup will lose 2 degrees. Are you people related to Al Gore?

It requires 1 btu (British thermal unit) to raise or lower 1 lb of pure water 1°F at sea level. That is called sensible heat.

It requires 144 btu to change the state of 1 lb of 32°F liquid pure water to 32°F solid ice at sea level. That is called latent heat of fusion.

To change the temperature of 1 lb of 212°F water to 32°F water requires the extraction of 180 btu. To change the state of that 1 lb 32°F water to 32°F ice requires a further extraction of 144 btu.

So you're simply talking about the extraction rate of btu (heat) from the water. The greater the temperature difference the faster the transfer rate.

Let's say you have #1 liquid at 200°F and #2 liquid at 100°F. After 10 minutes the 200°F #1 liquid cools to 100°F (-100 btu) while the 100°F #2 liquid only cools to 60°F (-40 btu).

Now #1 is 100°F and has the same transfer rate as #2 did (-40 btu) over the next 10 minutes while heat continues to be extracted from #2. So you can see that #1 can never catch up with #2.

Joe

So Scotty, your position is that a gram of water is a gram of water, that is it, it will always act the same. Reguardless of temperture, even physical state, gas, liquid or solid. In a way I agree, 1 gram of water in its solid form, ice, will turn to ice quicker than 1 gram of steam will. However that is not what we are talking about.

A good paper regarding this:

http://math.ucr.edu/home/baez/physics/General/hot_water.html
Untitled URL Link

A gram of water will always act like a gram of water in its given state. And it is the basis of the VERY simple initial question. In the real world the question is theoretical, just as the snowball proposition, and, to my mind serves the same purpose, to illustrate the myriad real-world variables that have to be taken into consideration.

I'm talking about water. If we want to talk about salt water, hard water or carbonated water, then that's another discussion. You quite rightly brought up the effects of friction on a snowball traveling at a high rate of speed. As to our freezing water, others have brought up issues such as solubility of gases and minerals in the water which will affect the outcome.

My teacher might have tossed in the volume of the snowball as another red herring to drag us through a calculation of its density. He could have called it an ice cube instead of a snowball. His aim was to pose the snowball as an isolated system to test a)our ability to state kinetic energy (joules) in terms of equivalent calories and b) our ability to distinguish between velocity and momentum, and how those factors apply to such a case. If kinetic energy in joules is equal to the one half the mass (in kg) times the square of the velocity (in m/s), it all becomes simple, and the mass is irrelevant to the required answer. It works with one gram (not much of a snowball!), 500 grams, 5 kilos (the head of a small snowman). They will all, in isolation, melt at the calculated velocity. The only difference will be the total number of joules/calories released to do the melting when it hits.

If I recall, those of us that got it doubled the mass of the snowball to 2kg for ease of calculation, set the required number of joules equivalent to 10,000 calories (to raise 2kg of water 5*C).

1/2*2*v-squared = 41,840 joules
v-squared = 41,840 joules
v = 41,840sq/rt
v = 204.54 m/s

That works out to about 450 mph, which is a pretty peppy fastball, so I don't expect anybody I know will me meltin' a snowball on my forehead.

Those that didn't get the answer for the most part reduced that velocity to 51+m/s to get back down to the given 500g mass.

As someone else pointed out, water can exist in both liquid and solid states at the 0*C freezing point and there is an exchange of energy involved in the transition either way that didn't enter into our high school calculations, and there are other factors that get into it, but the point of the exercise was that mass, in isolation, is irrelevant, to the calculation of heat exchange.

Which gets to other points made. Freezing water in an ice cube tray is an entirely different proposition from freezing water in a pipe. It's not just a matter of the surface area which may hinder or enhance the rate of heat exchange, but also the effects of pressure within a pipe as opposed to water free to contract or expand.

I don't mean to be a pain in the neck. I'm kind of enjoying the whole thread. Theory vs. real world.

I've done this experiment in several variations, numerous times. Cold water freezes faster than cold every time.

(quoted from post at 19:30:19 12/27/09) Not the same or even close to the question which weights more a ton of feather or a ton of bricks because a ton is a ton. Now if you said a ton of gold or a ton of feathers well then believe it or not a ton of feathers weights more then a ton of gold

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Not really. A ton is a ton is a ton. The catch you are referring to is which weighs more an ounce of gold or an ounce of feathers. Being that gold is weighed in troy ounces the feathers would weigh more as the troy ounce is less then a normal ounce. There is a troy pound but no such thing as a troy ton.

Scotty, my friend, I fear you are mixing up the first and second laws of thermodynamics. The second law indicates that heat can flow from a higher temperature region to a lower one, but not the other way around.

Not at all. Water will freeze when it has transerred enough of its own heat elsewhere. Ice will melt when enough energy is transferred to it from another source, whether that be a burner, ambient atmosphere or light. The heat to emit the snowball is created when the kinetic energy of the flying snowball is released on impact.

(quoted from post at 18:45:40 12/27/09) Well way back when I was in school they always told us the water would freeze faster if it was hot. So which is it does hot water freeze faster then cold??? Also back up why your answer is the correct one. Been thinking about setting some water out but it is to cold and I'm to lazy plus watching water freeze might get boring LOL

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Weigh the cubes from the hot and cold trays. The hot cubes are smaller and lighter which freeze faster.
Partly lower density and partly evaporating away prior to freezing.

I'm tickled to find another reader of John Baez here. Unfortunately it is clear that no posters subsequent to your mention followed and read the linked URL.

(quoted from post at 19:57:23 12/27/09) A good paper regarding this:

http://math.ucr.edu/home/baez/physics/General/hot_water.html
Untitled URL Link

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Agreed.

Science and Engineering ABOVE ^^^ Common Sense and Reasoning Below VVVVVV Same results!! To all others..... Al gore and others can, and do, justify anything they want you to believe by whatever means they can get their hands on. If the shoe fits.......