Thermal Physics

•  Internal energy - the total energy of all the particles.
• Temperature - the average kinetic energy of each individual particle.
• Melting point - the temperature at which a solid turns into a liquid. 
• Boiling point - the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure of the liquid’s environment, causing the liquid to turn into a gas.
• Evaporation - when a liquid turns into a gas without reaching its boiling point.
• Evaporation only occurs at the surface of a liquid; particles with enough kinetic energy break free and turn into gas particles.
• There are three factors that affect evaporation:

  1. Increasing the size of the surface area
  2. Increasing the temperature of the liquid
  3. Creating a draught of air over the surface to speed up evaporation
• Heating up an object = expands

  Cooling down an object = contracts
• When the particles are heated up, they move faster. This also means that they become further apart, causing an increase in volume when the object is heated. 
• Brownian motion - the observation of the movement of other particles in a fluid that seemingly move on their own.

  Their movement is actually caused by the random movement of fluids, which collide with the larger particles to make it seem like they’re moving on their own.
• In Brownian Motion, the fluid particles (gas and liquid) cannot be seen through the microscope as they are too small. 
• Pressure of a gas - the impact of gas particles as they collide with the walls of the container that they are in.
• Boyle’s Law - when there is a decrease in volume of a gas, there is an increase in pressure of the gas.
• Thermal capacity - the energy needed to increase the temperature of a substance by 1℃.
• Specific heat capacity - the energy needed to increase the temperature of 1 kg of a substance by 1℃.
• Latent heat - the energy needed to change a substance from one state to another WITHOUT changing the temperature of the substance.
• Specific latent heat - the energy needed to change 1 kg of a substance from one state to another WITHOUT changing the temperature of the substance.
• SOLIDS:

  • Strong forces of attraction
  • Vibrates at a fixed position
  • If heated, its internal energy increases (gain energy and vibrate more)
• LIQUIDS:

  • Forces of attraction are not strong enough to keep molecules in a fixed position
  • If heated, internal energy increases since molecules move faster
• GAS:

  • Force of attraction are negligible
  • Molecules move at high speeds, colliding with each other
  • If heated, its internal energy increases 
• solid --> liquid is melting
• liquid --> solid is freezing
• liquid --> gas at a certain temperature is boiling
• liquid --> gas below boiling point is evaporation
• gas --> liquid is condensation
• In evaporation, the average kinetic energy of the remaining molecules in the liquid decreases, so the liquid becomes cooler