Wikijunior:Particles/Summary

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

 * $$\text{Density} = \frac{\text{Mass}}{\text{Volume}}$$
 * 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