Temperature

• Heat and temperature are not the same
• Temperature


  A measure of how hot or cold something is
• Heat


  A form of energy that flows from a hotter object to a colder object, also known as thermal energy
• Heat transfer


  Energy transferred from one body to another, causing temperature changes
• Example of heat transfer


  • When a pan with water is placed over the fire, heat causes the water temperature to go up
• Thermometers are used to measure temperature
• Thermometers


  • Work because the fluid inside them expands when heated
• Heat


  The amount of thermal energy transferred from one body or system to another
• Main effects of heat

  • Changing states of matter
  • Expansion
  • Contraction
• Temperature


  The amount of heat in a system
• Temperature scales


  • Degrees Celsius (°C)
  • Degrees Fahrenheit (°F)
  • Kelvin (K) - SI unit of temperature
• Heating water


  1. As water is heated, the temperature increases steadily

  2. Solid state: water molecules gain kinetic energy and move faster

  3. Liquid state: water molecules move even faster, more kinetic energy is taken in, more movement and attractive forces break, molecules can escape as a gas

  4. When ice is heated, temperature remains constant at the melting point, 0°C

  5. When water boils, temperature remains constant at the boiling point, 100°C
• Increasing heat energy


  Results in an increase in temperature and changing physical state
• Expansion and Contraction


  1. When a material is heated, it expands; when cooled, it contracts

  2. Most materials - solids, liquids, and gases expand when heated and contract when cooled
• Convection


  1. Heat transfer by the bulk movement of molecules within fluids such as gases and liquids

  2. Heat transfer in fluids by the actual motion of matter
• Convection happens in liquids and gases
• Convection may be natural or forced
• Convection involves a bulk transfer of portions of the fluid
• How is Heat Transferred through Convection?

  When a fluid is heated from below, thermal expansion takes place. The less dense, hotter part of the fluid rises up, and the colder, denser fluid replaces it. This process is repeated as the heat is transferred through convection
• Land and sea breezes

  • Sea breeze
  • Land Breeze
• Sea breeze


  The sun heats up both the sea surface and land. The temperature above the land rises and heats the air in the atmosphere above it. Warm air expands and rises, cooler air over the sea rushes in and takes its place, creating the sea breeze
• Land Breeze


  During the night, the land and sea start cooling down. The air above the sea, being relatively warmer, expands and rises. The cooler air above the land sets up a flow of cool breeze offshore, known as the land breeze
• Heat energy


  Transferring it from one place to another
• Types of heat transfer

  • Conduction
  • Convection
  • Radiation
• Conduction


  The transfer of heat when particles collide
• Conduction


  • Takes place in solids because their particles are closely packed and touching each other
  • All solids conduct heat to some extent but some conduct heat better than others
  • All metals are good conductors
  • Nonmetals are poor conductors or good insulators
  • Metals are better conductors than other solids because they possess free delocalised electrons
  • Electrons are delocalised as they are not held in one place
  • When a metal is heated, delocalised electrons gain kinetic energy and move faster throughout the metal from the hot end to the cold end
  • Heat energy is transferred from one place to another both by the vibrations of molecules as well as by the movement of free electrons
  • When one part of the solid is heated, the heat gives energy to the particles causing them to vibrate and pass on this heat to other particles next to them
  • This causes the heat to travel through the solid until the entire solid is heated
  • Because the particles are further apart in liquids and gases, conduction does not take place in them as readily as in solids
  • The pot handle would be made of a good insulator such as plastic or wood so that it feels cooler when held
• Conduction takes place in solids because their particles are closely packed and touching each other
• All solids conduct heat to some extent but some conduct heat better than others
• All metals are good conductors
• Nonmetals are poor conductors or good insulators
• Metals are better conductors than other solids because they possess free delocalised electrons
• Electrons are delocalised as they are not held in one place
• When a metal is heated, delocalised electrons gain kinetic energy and move faster throughout the metal from the hot end to the cold end
• Heat energy is transferred from one place to another both by the vibrations of molecules as well as by the movement of free electrons
• When one part of the solid is heated, the heat gives energy to the particles causing them to vibrate and pass on this heat to other particles next to them
• This causes the heat to travel through the solid until the entire solid is heated
• Because the particles are further apart in liquids and gases, conduction does not take place in them as readily as in solids
• The pot handle would be made of a good insulator such as plastic or wood so that it feels cooler when held
• Radiation is the transfer of heat through a vacuum
• The Earth is separated from the sun by a vacuum of space