< Wikijunior:Particles

Introduction

  • Properties of matter
    • Matter must have mass
    • Matter must take up space

Matter

  • Different kinds of matter
    • Solids' shapes cannot be altered, and nor can its volume
    • Liquids' shapes can be altered, but not its volume
    • Gases' shapes can be altered, and so can its volume
  • Change of states
    • Solid → Liquid: Melting
      • Happens at a fixed temperature
    • Liquid → Solid: Freezing
      • Happens at a fixed temperature
    • Gas → Liquid: Condensation
      • Does not happen at a fixed temperature
    • Liquid → Gas: Boiling
      • Happens at a fixed temperature
      • Evaporation does not happen at a fixed temperature

Particle theory

  • Matter is made of particles;
  • Particles are infinitesimal, and current scientific instruments cannot see them;
  • Different kinds of particles have different sizes;
  • There must be gaps between particles
  • Particles are always in motion.

Diffusion

  • A common phenomenon observed in particle movement
  • Particles always go to a place of lower density

Brownian motion

  • When particles collide, they move in random directions
  • Observed in smoke cells
  • Discovered by Robert Brown
    • In 1827
    • While observing pollen grains

Particle model

  • A model that mimics the movement of particles
  • Can explain:
    • The three states of matter
    • Gas pressure
    • Density
    • Thermal expansion and contraction
  • Heat makes particles move more vigorously

Three states of matter

  • Solid
    • Particles cannot move freely
    • Particles only vibrate in fixed positions
    • Particles take on a fixed shape
  • Liquid
    • Particles do not take on a fixed shape; their shape depends on that of their container
    • Particles have a fixed volume
    • Particles can slide over one another
    • Particles do not move as freely as those in gas
  • Gas
    • Particles move freely in all directions
    • The shape and volume depend on that of the container

Gas pressure

  • Refers to the pressure exerted on a surface by gas
  • Measured
    • in Pascals, or 'Pa'
    • With a Bourdon gauge or pressure sensor
  • Appears in air, in which case it's called air or atmospheric pressure
  • Vacuum
    • Absence of air
    • Magdeburg hemispheres
      • Two hollow hemispheres form an empty sphere
      • The hemispheres cannot be separated
      • The air pressure on the outside greatly exceeds that of the inside

Density

  • If an object is submerged in a liquid or gas, it:
    • Floats if its density is less than that of the liquid or gas
    • Sinks if its density is more than that of the liquid or gas
  • Density of water = 1
  • Hot-air balloons
    • There is an engine in the balloon
    • As the engine is heated, the particles inside the balloon move more and are therefore further apart
    • As density of the air inside the balloon deceases, it floats.
  • Ships
    • The overall density of ships are under that of the water because there is a lot of air inside
  • Submarines
    • Whether it is submerged or surfaced depends on the ballast tank
    • When the ballast tank is filled with seawater, it sinks
    • When the water is pumped out, it surfaces

Thermal expansion and contraction

  • Particles move more vigorously when heated, and are further apart as a result
  • This makes the object larger, or expands
  • When they are cooled, the particles move less vigorously and are closer together
  • The object is made smaller, or contracts
  • Bimetallic strips
    • Made of two metal strips composed of different metals
    • The metals do not expand to the same extent
    • The strip bends when heated as a result
    • Used in
      • Thermostats
        • The connection is cut off when an appliance is too hot
        • The bimetallic strip in the appliance expands and therefore no longer completes the circuit
      • Fire alarm
        • The circuit is closed when the fire alarm is too hot
        • This makes the alarm ring because the built-in bimetallic strip completes the circuit
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