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Density and the Particle Model

Differences in the density of solids, liquids and gases can be explained using the particle model of matter.

Solids

Solids

  • Solids are the most dense state of matter.
  • The particles are packed tightly together.
Liquids

Liquids

  • Liquids are less dense than solids but more dense than gases.
  • The particles in liquids can move around each other.
Gases

Gases

  • Gases are the least dense state of matter.
  • The particles are free to move with negligible (tiny) forces between particles.

Calculating Density

To find out the density (density=mass/volume) of an object, we measure its mass and volume. We can measure the mass of an object using a balance (scales). We can calculate the density of:

Liquids

Liquids

  • For measuring the density of liquids, place a measuring cylinder on a balance and set the reading to zero.
  • Pour the liquid into the cylinder and write down its mass and volume. Then calculate the density.
Irregularly shaped solids

Irregularly shaped solids

  • For solids, we can use the Law of Displacement to estimate its volume.
  • This is done using a displacement can, or a graduated measuring cylinder.
  • The volume of displaced water is measured, and this is the volume of the object.
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