Does cold water weigh more than hot water. I think that it does.....but im not sure...

Hum,
per volume, yeah...

You should have asked about ice....

Maximum density is reached at 4 degrees celsius, so very cold water weighs less than water at 4 degrees.

Hum,
http://www.lsbu.ac.uk/water/images/anomal3.gif

From Here (http://www.lsbu.ac.uk/water/anmlies.html) (Forty-one Anomalies of Water)

Maximum density is reached at 4 degrees celsius, so very cold water weighs less than water at 4 degrees.Most of the deep-water ocean environment is at a pretty constant 4ºC (except around geothermal vents etc.) regardless of lattitude or surface temps. I think it is because that is the most dense temperature and to change temperature either up or down you have to fight the pressure.

-Dale

Can some one explain this?

weight=(mass)(Acceleration due to gravity)

wouldn't they have the same mass, regardless of temp; the acceleration should be the same too?

The point is that the same volume of water will have more mass at 4º than at another temperature. Since it has more mass the weight will be greater according to the equation you mentioned.

-Dale

So the molecules are moving slower which means there is room for more molecules?

In a way, but it is more due to how water molecules interact with each other (hydrogen bonding between the oxygen of one water molecule, and a hydrogen of another).

mass is same, weigt is more in cold though. learned that last year, also if you drop something in it, it would take longer for it to go through.