## Hot water is heavier than cold water.

Hot water is heavier than cold water.

If density is decreasing means its cover area is also increasing, and weight is irrelative to the area body occupies. Isn't it?

W=mg, to vary the weight we have to cop with its mass and gravity.
As gravity is constant then is it the mass of the water that is varying???

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 If you tried to measure it with typical scales and instruments you'd find hot and cold water weigh the same. But all energy has an equivalent mass which participates in gravitatational attraction. Therefore the heated water is a very tiny bit heavier than cold water.

 Quote by neduet Hot water is heavier than cold water. If density is decreasing means its cover area is also increasing, and weight is irrelative to the area body occupies. Isn't it? W=mg, to vary the weight we have to cop with its mass and gravity. As gravity is constant then is it the mass of the water that is varying???
Liquid water is most dense at 4 C.
so your statement "Hot water is heavier than cold water." if you mean a certain volume of water is true only from 0 C to 4 C.

This is also true,
W = density x volume x g, where density x volume = mass

So you can state either of the following:( increasing temperature above 4 C )
and neglecting the very tiny energy increase as per Antiphon
1. I start with a container of volume V containing water. Increasing the temperature will decrease the density of the water. Therefor, as I increase the temperature of the water, the water will expand and less mass of water will fill the volume V, due to the density decrease, and the water in volume V will now weigh less than before the temperature increase.
2. I start with a container of volume V containing water. Increasing the temperature will decrease the density of the water. Therefor, as I increase the temperature of the water, the water will expand and I need a larger volume V2>V to contain the water, which has the same mass and thus the same weight as before the temperature increase.

## Hot water is heavier than cold water.

Water is made of tiny pieces called molecules. Heat makes molecules excited. They jump around and move quickly! They need space to do this. Cold, on the other hand, makes molecules slow down and it can make them nearly stop. They don’t need as much room to move around and the space between them shrinks, It would seem that cold water would have to be denser than warm water

Mentor
 It would seem that cold water would have to be denser than warm water
This is true above 4°C. Below that, water forms more and more hydrogen bonds, which increase the volume and therefore reduce the density.

 Hot water is heavier than cold water.
Only if you want to include relativistic effects, which are extremely small here.

However, if you put real hot and cold water (of the same amount) on a very precise scale, you might measure a smaller value for hot water, as it needs more volume and therefore gets more buoyancy due to the air.

 Recognitions: Gold Member Science Advisor We should really get this thread in proportion I think. It starts off with a very ill defined statement "Hot water is heavier than cold water." and, instead of dealing with that, the thread leaps into relativity. I think that the OP may need to be expanded and clarified; it really doesn't mean a lot of sense to me, as it stands. Could we start walking before we try to run?
 If we look to what Einstein uncovered where mass is proportional to energy we can see that as we heat the cold water to a higher temperature giving the water a higher thermal energy this would give us a larger mass in theory and in experimentation. But you would need a very precise measuring system because the difference in mass would be extremely small compared to the overall weight. So yes, it makes sense that hot water is heavier than cold water but in normal/every day practices it's not very practical to even consider it or take it into consideration.