For example, most “full view” iceberg pictures I’ve seen, the iceberg has been vertically oriented – if ice is less dense than water, wouldn’t it at least be horizontal, with more than 10-15% of the mass visible above water?
In: Physics
The density of ice is about 90% that of water. That means that, if you attempted to fully submerge the iceberg (assume for a moment that you can), whatever volume of water the iceberg displaced, the water would push back with a bouyant force of ~110%* the weight of the iceberg. That forces the iceberg up a bit, until there is equilibrium, where the submerged portion of the iceberg elicits enough bouyant force from the water to balance its weight.
To think about it more intuitively, contrast this with a bag of air that you attempt to fully submerge in the water. The bag is going to eventually just float on top of the water surface, unsurprisingly because its density is just 0.1% that of water. Put a weight in the bag of air and it will submerge a little more. Add more weight until the average density of the bag matches that of ice, and you’ll find that only about 10% will be submerged, like an iceberg.
* This happens because, whatever *volume* of fluid you displace, the surrounding fluid will push back with enough force to support the *weight* of the missing fluid. This phenomenon is why hot-air balloons and helium balloons can float.
First of all, I don’t know that ELI5 and the density concept really fit together. But oh well.
My explanation goes like this:
Ice is less dense than water, but only slightly. On the other hand, it is much (!) more dense than air. So its “desire” to leave the air towards gravity (sink) is stronger than its “desire” to leave the water away from gravity (float).
It’s a matter of mow much less dense than water ice is. Basically, something less dense will float until enough material is out of the water that the submerged volume and total weight reach a matching density point with the water.
For example, let’s say you’ve got a cube of styrofoam that’s half the density of water. When you put it in water, half of the volume will submerge, because the total weight/half the volume = the density of water.
Ice is only about 9% less dense than water, which by the rule above means that only about 9% of the volume will be above the water line.
The amount of ice exposed is directly related to how much less dense ice is vs liquid water. Ice is 10% less dense, therefore 10% of the ice sticks out of the water. The 90% that is underwater is the same mass as the water it is “pushing” out of the way.
It’s 10-15% less dense. That means 10-15% of it is going to be above water.
And object that floats will displace a volume of water that has weight equal to itself. Then the remaining volume of said object will be above the water.
Objects that are less dense that water. Are going to have a different percentage of their volume of above the water based on their density. That’s why say…a balloon filled with air will be almost completely above water. Air has a very low density.
Edit: oh, and they end up being vertical because that’s more stable. If it was horizontal and one side was even slightly heavier eventually that side would sink in and “flip” the object into a vertical position. Even if it were horizontal though it would still only have 10-15% of its volume above water, of course.
Let’s say you take something else that floats on water, like the human body, when laying flat your weight is spread over a wider area, making you able to float, but do you try to stand straight up in water you start to sink because all your weight is confined to a smaller point. It’s the same for icebergs, ice may be leas dense then water, but if you add enough weight in one spot it will sink
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