eli5: Why does adding salt increase the buoyancy of water?
In: Chemistry
Buoyancy provided is the equivalent to the weight of the water displaced by a floating object. Adding salt increases the density of the water, meaning less water needs to be displaced to provide the same buoyancy, making it “more buoyant” than plain water
Adding salt to water increases the buoyancy of things floating in the water, not of the water itself.
The buoyancy of things floating in the water increases when you add salt because salt water is denser than fresh water. Salt water is denser than fresh water because salt and other contaminates can actually “sit” in between the molecules of water increasing the mass without increasing the volume.
In layman’s terms, adding salt increases the density.
The density of fresh water is about 1,000kg/m^3 – regular floaty floaty.
The density of the Dead sea is about 1,240kg/m^3 – you’ll bob about in it like a cork, lots of floaty floaty.
The density of mercury (liquid metal at room temperature, not the planet) is about 13,546kg/m^3 – so much floaty floaty that solid iron anvils will bob about on the surface like corks.
https://www.technology.org/2018/05/31/how-can-a-heavy-iron-anvil-float-on-liquid-mercury-video/
Hope this helps with the mental picture.
You might have noticed that “lighter” objects (more precise: less dense objects) swim better than “heavier” objects, if both are in the same fluid. The reverse is also true: the same object will swim better in a heavier fluid (in technical terms: buoyancy results from a difference in density).
Saltwater is heavier than freshwater. Not so much you’d notice it when holding a glass full of it, but enough that you notice it when you try to dive with your lungs full of air.
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