Heat energy

• Particles that make up matter are in constant motion. They vibrate.
• In fluids, the particles move from place to place.
• Anything that moves has kinetic energy.
• An object is hotter on average if its particles have more kinetic energy.
• Temperature is measured using thermometers.
• An object is colder on average if its particles have less kinetic energy.
• Temperature measures the average kinetic energy that the particles of an object have.
• Units of temperature:

  • Celsius (°C)
  • Kelvin (K)
• The Celsius scale defines 0 degrees as the temperature that water freezes.
• The Celsius scale defines 100 degrees as the temperature that water boils.
• The normal body temperature is 36 to 37 degrees Celsius.
• The normal room temperature is 20 degrees Celsius.
• Absolute zero is the temperature where particles stop moving completely. It is the lowest possible temperature.
• Absolute zero: 0K or -273 degrees Celsius.
• If two objects of different temperatures are placed in contact with one another, the hotter one cools down and the colder one warms up until they are both the same temperature.
• Particles in a hotter object will lose kinetic energy and the particles in a colder object will gain kinetic energy from the hot one.
• The amount of energy transferred is called the heat energy.
• Heat is measured in joules (J).
• How much the temperature changes based on the heat energy depends on:

  • The material
  • The number of particles
• If the bond between particles is weak, a small transfer of heat energy can result in lots of extra vibration, therefore a large increase in temperature.
• If the heat energy is shared between a lot of particles, the average increase of kinetic energy per particle will be small.
• Heat energy causes the particles to move faster.
• Expansion also causes the density to reduce.
• The transfer of heat energy can cause bonds between particles to break completely, resulting in a change of state.
• During changes of state, the kinetic energy doesnt increase, so the temperature does not rise.
• Conduction is the transfer of energy from particle to particle.
• Conduction is the most effective in solids.
• Poor conductors are called thermal insulators.
• Convection is the transfer of energy as particles move from place to place.
• Convection only happens in fluids.
• Convection occurs because of the difference in density of the hotter and colder fluids.
• In convection, the cold fluid is more dense so its sinks, pushing the less dense hotter fluid up.
• As particles vibrate, the emit Infrared Radiation (IR).
• While emitting IR, the particles lose energy and slow down while making the temperature of the object drop.
• The faster the vibrations, the more IR emitted. Causing the hottest objects to emit the most IR.
• When particles absorb IR, they gain energy and move more, causing them to heat up.
• Dull or dark coloured surfaces are good at absorbing and emitting IR.
• Shiny or light coloured objects are bad at absorbing and emitting IR. They reflect it, away from the object on the outside and back into the object on the inside.
• IR does not require any particles to travel between them, so it can transfer heat energy through solids, liquids, gases and vacuums.
• The suns heat reaches earth through IR.