Thermal Physics

• Matter


  Can be described by its outer shape and the behavior of its molecules
• Solids


  • Fixed shape and volume, with molecules closely packed, vibrating in place, and strongly bonded
• Liquids


  • No fixed shape but have a fixed volume, with molecules loosely packed, sliding over each other, and still strongly bonded
• Gases


  • No fixed shape or volume, with molecules very spread out, moving freely and quickly, and having very weak or virtually no bonds
• Temperature


  The average kinetic energy of the molecules in a substance
• Molecules


  Have both kinetic energy (due to movement) and potential energy (due to attraction to each other)
• Internal energy increases


  When a substance is heated because molecules move faster and farther apart
• A gas has no fixed shape or volume and takes the shape and volume of its container
• Absolute Zero


  The coldest temperature in the universe, where molecules have no kinetic energy
• Kelvin scale


  The same as the Celsius scale, but shifted so that absolute zero is at 0 Kelvin
• Converting between Celsius and Kelvin

  1. To convert Kelvin to Celsius, add 273

  2. To convert Celsius to Kelvin, subtract 273
• Changes in State


  1. When a substance is heated, its temperature rises as molecules move faster

  2. At the melting point, a solid changes to a liquid, and the temperature remains constant during melting

  3. During boiling, a liquid changes to a gas, and the temperature again remains constant

  4. The temperature stays constant during melting and boiling because the energy is used to weaken and break bonds between molecules, not to increase kinetic energy

  5. The same principle applies during condensation and freezing, where energy is used for potential energy instead
• Evaporation


  Occurs when the most energetic molecules on a liquid's surface break their bonds and escape, transforming the liquid into a gas
• As evaporation progresses


  The remaining liquid loses energy, resulting in a decrease in temperature
• Sweating helps regulate body temperature as sweat absorbs heat from the body during evaporation
• Factors that increase the rate of evaporation

  • Heating the substance
  • Increasing the surface area of the liquid
  • Introducing air currents or wind
• Thermal Expansion


  When heated, the volume of a substance increases as the molecules move faster and further apart
• Gases expand more than liquids, and liquids expand more than solids due to the strength of their bonds</b>
• Thermal expansion depends on temperature and the initial size of the object, with longer objects expanding more than shorter objects
• Thermal expansion can cause problems such as buckling of railway tracks and contraction of electrical cables, which can be addressed by allowing for expansion and contraction
• Brownian Motion


  The random and jerky motion of dust particles in the air due to collisions with fast-moving air molecules
• Pressure


  The force applied over a large area of the container due to the collision of gas molecules with the walls
• As temperature increases


  The volume of a gas increases, and they are directly proportional
• As temperature increases


  The pressure of a gas also increases, and they are directly proportional
• Pressure and volume


  Are inversely proportional
• PV = constant


  Relates pressure and volume, where P is pressure, V is volume, and the constant represents the initial conditions
• Heat transfer methods


  • Conduction
  • Convection
  • Radiation
• Conduction


  The transfer of heat through direct contact between objects
• Convection


  The transfer of heat through the movement of a fluid (liquid or gas)
• Radiation


  The transfer of heat through electromagnetic waves
• Metals are good conductors of heat, while wood and plastic are poor conductors
• Convection occurs when a heated fluid rises and is replaced by cooler fluid, creating a convection current
• Radiation does not require a medium and can occur in a vacuum
• The sun's heat reaches Earth through radiation
• Specific Heat Capacity (C)


  The amount of heat energy needed to raise the temperature of one kilogram of a substance by one degree Celsius
• Equation for Specific Heat Capacity

  C = E / (m * ΔT), where C is specific heat capacity in J/kg°C, E is the heat energy in J, m is the mass of the substance in kg, and ΔT is the change in temperature in °C
• Equation for Heat Energy (E)

  E = P * t, where E is the heat energy in J, P is the power in W, and t is the time in s
• This equation can be substituted into the equations for specific heat capacity (C) and latent heat (L) to find the values of C or L