Pressure and Density
- How heavy something is for its size (how tightly packed the particles are)
- Density = Mass / Volume
- The units for density are: g/cm2 or kg/m2
- (If you do not know the volume of an object, immerse it in water and measure the displacement.)
- The force that is being applied to something.
- Pressure = Force / Area
- Units of pressure are: Pa (pascals) or N/m2
- If a force is applied on a large area, the pressure is lower than the pressure of the same force on a smaller area.
- In gases and liquids the pressure acts equally in all directions and the pressure increases with depth.
- For liquids and gases: Pressure Difference = Height x Density x g (10)
Changes of State
Solid --melts-> Liquid --evaporates-> Gas --condenses-> Liquid --solidifies-> Solid
- Strong forces of attraction between particles with little energy and very small vibrations.
- Fixed in a regular arrangement.
- Weaker attractions with more energy and random movements at a low speed.
- Close but moving particles, arranged irregularly.
- No attractions between particles.
- High energy, random movements at high speeds.
Evaporation --> Particles escape from liquid to gas. They have to be moving near to the surface of the liquid at a high speed and in the right direction (enough kinetic energy).