Chapter: Heat

• Introduction to Heat

  • Definition: Form of energy that causes a sensation of hotness
  • Temperature: Measure of the degree of hotness of an object
  • Units: Degree Celsius (°C), Fahrenheit (°F), Kelvin (K)
  • Measuring Instrument: Thermometer

• Measuring Temperature

  • Clinical Thermometer
    • Purpose: Measuring human body temperature
    • Range: 35°C to 42°C
    • Normal Human Body Temperature: 37°C (or 98.6°F)
    • Special Feature: Kink prevents immediate fall of mercury level
  • Laboratory Thermometer
    • Purpose: Measuring temperature of water and other objects
    • Range: Usually -10°C to 110°C
    • Precautions: Keep upright, immerse properly, do not touch container walls

• Transfer of Heat

  • Direction: Flows from a hotter object to a colder object until temperatures are equal
  • Modes of Transfer: Conduction, Convection, Radiation

• Methods of Heat Transfer

  • Conduction
    • Definition: Process of heat transfer from hotter end to colder end in solids
    • Conductors: Materials that allow heat to pass easily (e.g., metals like iron, copper, aluminum)
    • Insulators (Bad Conductors): Materials that do not allow heat to pass easily (e.g., wood, plastic, paper, water, air)
  • Convection
    • Definition: Transfer of heat by the movement of fluids (liquids and gases)
    • Mechanism: Hot fluid rises, cold fluid sinks to take its place
    • Natural Phenomena: Land Breeze and Sea Breeze
      • Sea Breeze: Day time, wind blows from Sea to Land
      • Land Breeze: Night time, wind blows from Land to Sea
  • Radiation
    • Definition: Transfer of heat without any medium (can travel through vacuum)
    • Example: Heat from the sun reaching the Earth
    • Absorption: Dark-colored surfaces absorb more heat than light-colored surfaces

• Understanding Clothing in Different Seasons

  • Summer Clothing
    • Preference: Light-colored clothes
    • Reason: Reflect most of the heat
  • Winter Clothing
    • Preference: Dark-colored clothes
    • Reason: Absorb heat
    • Woolen Clothes: Trap air between fibers (air is a poor conductor/insulator) to prevent body heat loss