Molecular Kinetic Theory Model

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Brownian Motion

Brownian motion was the first direct evidence of atoms.

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Robert Brown

  • Robert Brown noticed that tiny pollen grains suspended in still water moved about in random paths.
  • The pollen would change direction without colliding with other pollen grains.
    • This can be observed with a microscope for any small particles in a fluid.
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  • The random motion of the pollen grains is caused by atoms randomly colliding with pollen in the fluid.
  • This is direct evidence of atoms existing.

Pressure of an Ideal Gas

The pressure of an ideal gas is closely related to the temperature and volume.

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  • The pressure from a gas comes from molecules colliding with the wall of a container.
  • Pressure can be increased by:
    • Increasing concentration - collisions between molecules are more frequent if the molecules are packed together more tightly.
    • Increasing temperature - hot gases have more kinetic energy and so more collisions will happen.
    • Decreasing container size - this will increase the number of collisions.
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Temperature and volume

  • Pressure is linked to temperature and volume.
  • Consider pumping up an empty car tire.
    • Initially, the temperature will remain the same as the volume increases from a small increase in pressure.
    • Next, the pressure will increase a lot as the volume refuses to expand more.
    • Finally, the temperature will increase as the car is driven, this will increase the pressure.

Jump to other topics

1Measurements & Errors

2Particles & Radiation


4Mechanics & Materials


6Further Mechanics & Thermal Physics (A2 only)

7Fields & Their Consequences (A2 only)

8Nuclear Physics (A2 only)

9Option: Astrophysics (A2 only)

10Option: Medical Physics (A2 only)

11Option: Engineering Physics (A2 only)

12Option: Turning Points in Physics (A2 only)

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