# What is heavier, water or ice?

I was reading this link and I never saw a definite answer. One would think if you have 1000 pounds of water, and you froze it and weight it you would still have the same 1000 pounds of water when weighed at sea level. Even though there is less movement, right?

• Same mass, different density, so ice floats on water. Commented Oct 16, 2019 at 8:07

For all practical purposes the weight will remain 1000 pounds when you freeze it. In theory the mass of the water will reduce somewhat through cooling because it will contain less energy when frozen, but the effect would be utterly negligible.

Although the weight will be the same, water expands in volume by about a tenth as it freezes (which is why, for example, pipes burst in icy weather). Since it is therefore less dense, your frozen block of 1000 pounds of ice will float on water, but that is because its volume has expanded on freezing and not because its weight has reduced.

• +1 A more important effect would be the different buoyancy due to the ice's larger volume. It would be great if you could also add an estimation of this effect for completeness. Commented Oct 16, 2019 at 6:47
• @ahemmetter: To be fair to Marco, the question has nothing to do with volume, density, or buoyancy. Commented Oct 16, 2019 at 12:06
• @James Since the question specifies "weighed at sea level", the difference in buoyancy will be the largest deviation from the straight-forward answer (1000 pounds). Commented Oct 16, 2019 at 12:49
• @James, people who have not been educated in the physical sciences often say "weight" when they really are talking about density. Even though the question literally was, "which is heavier..." it is quite reasonable to think that the OP will be satisfied by an answer that talks about density. Commented Oct 16, 2019 at 13:58
• @ahemmelter 10% volume increase is 100 pounds of water volume. Air is 784 times less dense than air: 2 ounces of extra force.
– JEB
Commented Oct 16, 2019 at 14:34

Depends on how you are defining "weight".

If you mean weight as in the vector or scalar of the gravity acting on an object, Marco's answer is what you want.

There is a third meaning of weight. This is essentially "what a scale measures". This definition also fits with how people typically experience the effects of weight.

If we use that definition, then when standing on Earth, you could say your weight is what is countered by the normal force of the ground. By this definition, astronauts in orbit are also "weightless", even though they still have mass, and gravity acting on them.

Now, when you freeze the water, the mass stays the same (so the downward force $$mg$$ is the same); but the upwards buoyant force from the air increases, due to the increased volume. Since the mass stays the same and buoyancy increases, this means the net downward force of the ice block will reduce, and therefore it's "weight" as measured by a scale would decrease.

In the context of the Quora question, I think this third definition of weight is the most relevant; because it is the easiest way to measure weight, and is typically what a layperson thinks of when they consider "how much does this object weigh?". This is why people will say freezing water will reduce it's weight.

If it were weighted in a vacuum, you wouldn't expect to see a detectable change in weight due to freezing. But vacuum conditions aren't the typical human experience, and most people don't have access to a vacuum chamber with a scale in it.