6.2.6

Molecular Kinetic Theory Model

Test yourself

Brownian Motion

Brownian motion was the first direct evidence of atoms.

Illustrative background for Robert BrownIllustrative background for Robert Brown ?? "content

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.
Illustrative background for AtomsIllustrative background for Atoms ?? "content

Atoms

  • 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.

Illustrative background for Pressure Illustrative background for Pressure  ?? "content

Pressure

  • 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.
Illustrative background for Temperature and volume Illustrative background for Temperature and volume  ?? "content

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

3Waves

4Mechanics & Materials

5Electricity

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)

Go student ad image

Unlock your full potential with GoStudent tutoring

  • Affordable 1:1 tutoring from the comfort of your home

  • Tutors are matched to your specific learning needs

  • 30+ school subjects covered

Book a free trial lesson