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ELI5 Yahaaa

Heavy for its size

What Is Density?

Density is not weight. It is how much weight is packed into a given space.

A big light thing Lots of space, littlemassA small heavy thing Little space, lots ofmass
A kilo of feathers and a kilo of lead weigh the same. They do not take the same room.

  1. Step 1 of 5

    Weight alone tells you very little.

    A lorry of feathers Heavy overallOne marble Light overall

    A truckload of feathers outweighs a marble. That says nothing useful about the materials — only about how much of each you happen to have.

  2. Step 2 of 5

    Density is mass per unit of space.

    Gold19.3 g per cm³Iron7.9Water1.0

    Take exactly one cubic centimetre of a material and weigh it. That number is the density, and it belongs to the material itself.

  3. Step 3 of 5

    It depends on the atoms and the packing.

    Lead Heavy atoms, tightlypackedAir Light atoms, far apart

    Heavy atoms packed tightly give high density. Light atoms with lots of space between them give low density. Both matter.

  4. Step 4 of 5

    Density decides what floats.

    Oil — 0.9, floats on waterlessdenseWater — 1.0the referenceHoney — 1.4, sinksmoredense

    Anything less dense than water floats in it. Anything less dense than air rises through it — which is exactly what a helium balloon does.

  5. Step 5 of 5

    Heat changes it.

    1 Heat it2 Particlesspread apart3 It rises

    Warm anything and its particles spread out, so it becomes less dense and rises. That single fact drives hot air balloons, wind, weather and ocean currents.

    You can layer honey, water and oil in a glass and they will not mix — each finds its place by density.

The short version

Density is mass packed into space, and it decides what floats, what sinks and what rises.

Try it yourself

Pour honey, then water, then cooking oil into a glass. They settle into three stripes, heaviest at the bottom.

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