Temperature is all about particle motion. The hotter something is, the faster its particles move. This connection between heat and motion explains why things expand when heated and contract when cooled.

Heat always flows from hot to cold, seeking balance. This process, called heat transfer, happens through contact, fluid movement, or even invisible waves. Understanding heat flow helps us predict how materials will behave in different temperature situations.

Temperature and Kinetic Energy

Temperature and particle kinetic energy

• Temperature quantifies hotness or coldness measures average kinetic energy of particles in a system
• Kinetic energy associated with particle motion directly proportional to temperature
• Higher temperature faster particle motion higher average kinetic energy (boiling water)
• Lower temperature slower particle motion lower average kinetic energy (ice cube)
• Temperature scales: Celsius (℃), Fahrenheit (℉), Kelvin (K) absolute scale 0 K theoretical lowest temperature
• Molecular interpretation:
  • Gases: translational motion of molecules (air molecules)
  • Solids: vibrational motion of atoms (vibrating crystal lattice)
  • Liquids: combination of translational and vibrational motion (water molecules)

Heat Transfer and Thermal Expansion

Thermal equilibrium and heat transfer

• Thermal equilibrium occurs when objects have same temperature no net heat transfer (cup of coffee left on table)
• Heat transfers from higher to lower temperature objects (hot spoon in cold water)
• Heat transfer methods:
  1. Conduction: through direct contact (metal pot on stove)
  2. Convection: through fluid motion (hot air rising in a room)
  3. Radiation: through electromagnetic waves (sun warming Earth)
• Thermal equilibrium:
  • Basis for temperature measurement (thermometer in equilibrium with body)
  • Determines heat flow direction (from hot coffee to cold cream)
  • Influences heat transfer rate (faster transfer with larger temperature difference)

Thermal expansion in materials

• Thermal expansion increases object size as temperature rises due to increased atomic vibrations and separation
• Expansion types:
  • Linear: change in length (railway tracks)
  • Area: change in surface area (metal sheet)
  • Volume: change in volume (balloon in sun)
• Material properties:
  • Coefficient of thermal expansion measures expansion tendency
  • Crystal structure influences expansion behavior
• Material effects:
  • Metals expand more than non-metals (aluminum vs ceramic)
  • Liquids typically expand more than solids (mercury in thermometer)
  • Gases expand significantly with temperature increase (hot air balloon)
• Applications:
  • Expansion joints in bridges and buildings allow for movement
  • Bimetallic strips in thermostats bend with temperature changes
  • Precision instruments require temperature compensation (telescopes)

Calculations for thermal expansion types

• Linear thermal expansion: $\Delta L = \alpha L_0 \Delta T$
  • $\Delta L$: length change
  • $\alpha$: linear expansion coefficient
  • $L_0$: initial length
  • $\Delta T$: temperature change
• Area thermal expansion: $\Delta A = 2\alpha A_0 \Delta T$
  • $\Delta A$: area change
  • $A_0$: initial area
• Volume thermal expansion:
  • Solids: $\Delta V = 3\alpha V_0 \Delta T$
  • Liquids: $\Delta V = \beta V_0 \Delta T$
  • $\Delta V$: volume change
  • $V_0$: initial volume
  • $\beta$: volume expansion coefficient
• Problem-solving steps:
  1. Identify expansion type (linear, area, volume)
  2. Choose appropriate equation
  3. Gather information and convert units
  4. Solve for unknown variable
• Consider units consistency temperature scale conversions and material-specific expansion coefficients