# Why is water heavier than it looks?

## Main Question or Discussion Point

Why?

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haruspex
Homework Helper
Gold Member
I think this question belongs in the psychology section.

Bobbywhy
Gold Member
Better Best, Welcome to Physics Forums!

How heavy, exactly, does water look?

Cheers,
Bobbywhy

Well, idk. You're able to easily move it around and stuff but when you try to pick it up it takes effort.

Well, idk. You're able to easily move it around and stuff but when you try to pick it up it takes effort.

Would that make it heavy?

BruceW
Homework Helper
Well, idk. You're able to easily move it around and stuff but when you try to pick it up it takes effort.
no, it's not easy to move around. Its inertial mass and gravitational mass are the same.

Drakkith
Staff Emeritus
Would that make it heavy?
Water moves around things because it is a fluid. (It is also a liquid)
To quote wiki:

In physics, a fluid is a substance that continually deforms (flows) under an applied shear stress.
How HEAVY something may be is related directly to its mass.

Bobbywhy
Gold Member
Water moves around things because it is a fluid. (It is also a liquid)
To quote wiki:

How HEAVY something may be is related directly to its mass.
Oh, ok. Well then can you explain that to me? Because a balloon full of air and a balloon full of water the same size basically look similar, but the one with water is much heavier. How is that so if they're taking up the same amount of space? Stupid question, I know.

This may come as a surprise to you but your eyes are not scales. They detect light, not mass.

Last edited:
Drakkith
Staff Emeritus
Oh, ok. Well then can you explain that to me? Because a balloon full of air and a balloon full of water the same size basically look similar, but the one with water is much heavier. How is that so?
For a gas like helium in a balloon, there are FAR fewer atoms of helium that will fit in the balloon compared with water. This isn't because helium is "larger", it is because helium is a gas normally. The atoms are flying around very quickly and don't stick together at all like water does. Water molecules attract each other and are much heavier than helium atoms are, so they are much harder to turn into a gas. (Which is why water is a liquid all the way up to 100 Celsius while helium is a gas unless you cool it to around -270 Celsius)
See the following links for more.

http://en.wikipedia.org/wiki/Liquid
http://en.wikipedia.org/wiki/Gas

Borek
Mentor
Because a balloon full of air and a balloon full of water the same size basically look similar, but the one with water is much heavier. How is that so if they're taking up the same amount of space?
My troll detector goes "ping". This is a question children in preoperational stage may ask - that means, up to 7 y.o.

BruceW
Homework Helper
Oh, ok. Well then can you explain that to me? Because a balloon full of air and a balloon full of water the same size basically look similar, but the one with water is much heavier. How is that so if they're taking up the same amount of space? Stupid question, I know.
I'm going to assume no troll, and say the answer is density. You can imagine the water balloon has got more stuff inside, even though it has same volume as the air balloon. The ratio of 'stuff' to volume is density. (Or, more technically than 'stuff', I should say mass). In an equation:
$$density = \frac{mass}{volume}$$
And the density of different materials is different.

sophiecentaur