Density (Gravity)

On a flat Earth, not all directions are equal and that there is significance to the direction 'down' over any other. This is something many feel intuitively but here is scientifically formalised.

The driving force behind objects going down is their density rather then their mass. An object's motion is dictated by the density of their surroundings; if an object is denser, it descends. If it is less dense, it will go up. This is best demonstrated with reference to water. Less dense rock, like pumice, floats, while denser rock will sink immediately. However with salt water, where molecules of salt exist throughout the liquid and thus make it denser, more things will be able to float.

Should an object be put in water with a sufficient amount of salt that their densities are equal, the object will essentially be weightless.

Given that everything is typically denser than the air, the medium that surrounds us, we are forced down to the Earth. Less dense gases ascend.

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