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Science Sunday: How buoyancy works

Things float because of density. Specifically they float when they are less dense than the fluid you put them in.
Posted at 12:25 PM, Jul 10, 2022
and last updated 2022-07-10 15:36:58-04

BAKERSFIELD, Calif (KERO) — If you've ever wondered why something as small as a marble can sink, but something as large as ship can float, then you've thought about the science behind buoyancy.

In this edition of Science Sundays, we'll be experimenting with different densities to see whether or not things float and how it relates to buyoancy.

Items Needed:

  • Two glasses both filled with water
  • Two raw eggs
  • Salt

Fill one glass with fresh water. Grab a second glass of water and add 2 tablespoons of salt then stir to make your salt water. Drop one egg in each glass and watch as the egg in the salt water floats and the one in the fresh water doesn't.

Things float because of density, specifically they float when they are less dense than the fluid you put them in.

In our example, fresh water has a density of 0.99 grams per milliliter, and the egg has a density of 1.03 grams per milliliter. Since the egg is more dense it sinks.

Density is equal to mass over volume. Mass is the amount of matter, or the amount of stuff in an object. Volume is the amount of space that stuff takes up. When we add salt to water we’re adding more stuff so the mass goes up a lot, but the volume doesn’t change much since the salt dissolves in the water. That means the density increases, and salt water is more dense than fresh water.

So the more salt we add, the more dense the water will become, and the better the egg will float.