Why does cold water weigh less than hot water?

Question

Wow. Such a lot of different opinions. Having read them I am thinking this as an analogy.

Cold water = 1000 people standing on a trampoline (like inactive atoms) weigh x amount.

Hot water = 1000 people jumping on the trampoline (like active atoms) therefore not everyone's weight would be measured at the same time giving a weight less than x.

Who thinks this sounds right?

Thanks everyone. I have found this web site that gives a good practical example and explanation.

http://www.abc.net.au/science/surfingscientist/pdf/teachdemo10.pdf#search=%22cold%20water%20hot%20water%22

Answer 1

It does not always. That depends on the cold water temperature. Maximum density is 4 C above freezing (39.2 F). Water colder than 4 C is lighter than water at 4 C. Water warmer that 4 C is lighter than water at 4 C. And water will get less dense the hotter it gets.

Why is water colder than 4 C less dense? Because it is starting to arrange itself in a less dense matrix on the way to ice formation. Ice is less dense because the water molecules form "bridges" (hydrogen bonds) that leave some gaps. As temperature raise, the motion of the individual molecules get too large for the intermolecular bond to keep them in check, and the gaps reduces until maximum density is reached at 4 C.

Hope that makes sense.

Answer 2

As mentioned,
Cold water is denser than hot water. ( at the same pressure).

Temperature is the measure of molecular vibrational energy.
If you could see the molecules, they would be vibrating and banging into each other. The hotter the molecules(solid, liquid or gas), the more they are shaking and banging around.
If you cool them, there they will have less vibrational energy.
If you cool them to the point that they no longer have any vibrational energy, that is called Absolute zero. -273.15C, 0 Kelvin, -459F. So there is a lower limit to how cold you can get something, but no upper limit to how hot something can get.

For example, if you heat the air inside a balloon, it will get bigger, because the molecules are banging around into each other more.
Put it in the freezer, and it will shrink. The same is true for liquids. The molecules of water, are attracted to each other because water has a slightly positive end, and a negative end.
( polar ). This is why water molecules stick together, and why water is a liquid at room temperature. Heat it up, and the water expands slightly. Heat it up past the point that the attractive force holding together the molecules bouncing into each other, and the molecules are bounced away, and the water boils.
This occurs when the vapor pressure of the water equals the atmospheric pressure.

Answer 3

It depends on what you mean by cold or hot. Water weighs most at 4° C. In other words water is densest at this temperature. Water that is colder or warmer than 4° C is less dense or lighter than it is at 4° C. This is why ice floats.

Other than that, the molecules and atoms in water speed up when they get hot. This makes them spread apart and the water expands. The expansion makes the water less dense and therefore weigh less than colder water per given volume.

Answer 4

all water "weighs" the same for the same mass, regardless of the temperature.

At atmospheric pressure, the DENSITY of water is maximum, at about 39 degrees F. As it warms or cools from that point it expands, so the density decreases. As water freezes its density rapidly decreases -- so ice floats in water. The solid will sink in the liquid phase for almost all other substances.
Think of all the things which would be different if ice were more dense that liquid water and "sunk".

Answer 5

Other way around. Cold water does weigh more than hot water because it is more dense at a
colder temperature. The strange thing about this behavior is that once the
water freezes and forms ice, the ice is less dense than the water.

Answer 6

That is not correct. Your example is incorrect. There is no difference. The water in the beaker, hot or cold all of the time and not jumping into the space above the beaker so that the weight of those molecules would not be present in the weight.

Answer 7

It is the other way around. The molecules in cold water are less excited than in hot water. They are closer together and the water is denser. It you measure the same volume of water, the cold water will weigh more.

Answer 8

even with being dealt with as incompressible, water does enhance/settlement slightly less than temperature variations. usually it is going to enhance really (even as above freezing) because it really is heated; so its unique volume v --> V a more effective volume the position V > v. once you've a beaker with fixed volume W = v, the water will be purely contained in that beaker. yet even as heated, assuming the beaker volume does not replace, and v --> V, we may have V - W = e > 0 and a number of that water (e) will spill over the lip. it really is, countless the mass will flow over the facet. hence, the beaker and the most suitable water in it is going to weigh decrease than even as the water became cooler. issues are really diverse even as the water freezes or boils even with the undeniable fact that. therefore, what became written above assume hotter than freezing and below boiling.

Answer 9

Acctually i think hot water weighs less then cold water. And if thats what you meant its because the molecules are moving much faster in hot water but in cold water they are just standing still which would make it heavier.

Answer 10

Those who said cold water weighs more are correct. From a text on Fluid Mechanics, the density of water at 40 F = 1.940 slugs/cu ft, at 200F it drops to 1.868