# Why does density decide whether something floats or sinks? [duplicate]

Possible Duplicate:
Balloons and lifting gases

I understand that density of an object dictates whether or not it will float, but what I don't get and can't get any satisfactory explanation... What causes an object of lower density to float?

Can someone clarify? Differences in pressure ( a little more on that) ?

Thus far, I've rationalized it in this way ( I sense it's wrong, but still):

Object with a lower density has a spread out mass distribution along the volume and therefore, the contact surface. Since water's density is 1 g/cm$^3$ ( our definition of mass says that 1 g is equal exactly to a 1 cm$^3$ volume of water)... When you have an object with a lower than water density, it exerts a force on the water due to gravity, but because at every specific point the weight of the object is always less than the one of water, it is unable to clear its volume of water out.

I know, doesn't make any sense, please help! Every explanation on the Web just says it's dependent on the density of the object and that's that.

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## marked as duplicate by David Z♦Sep 6 '11 at 1:17

I think this is covered by the various questions that have been asked here about buoyancy, including the answer I posted to the linked (duplicate) question explaining how buoyant force arises from pressure differences in the fluid. If that doesn't satisfy you, though, you can edit this question to explain what you're still confused about and I'll reopen it. –  David Z Sep 6 '11 at 1:19