Heat Energy

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Heat ALWAYS flows from a warmer region to a cooler region!!!

Different metals conduct heat energy differently to others. Conduction is the transfer of heat energy (in this example) from atom to tom in contract with each other. Heat vibrates atoms faster, and the vibrations cause bumping and vibration in the next atom, and so on.

*Other conduction might be air getting hot when it touches a hot element.

Flasks with different exterior coatings (black, silver, colourless) radiate heat energy differently to others. Radiation is the movement of infra-red energy from a hot place to a a colder doge.

Silver surfaces radiate heat back into the water, so this stays hotter for longer. Black surfaces absorb heat well, but also radiate out too. A lot of energy radiates away from the water, so it gets colder sooner.

Conduction: Heat energy is transferred from a hot place or surface onto another surface that is less hot. Contact between the substances allows conduction. Grabbing a hot spoon hurts because heat energy is conducted from the spoon to your hand. Cold bodies going into hot showers feel warmer because heat energy of the water is transferred by conduction onto your skin. A stone surface that was out overnight is cold, and it feels hot because your foot's heat energy is transferred by conduction to the stone. Walking over hot coals does not burn because you are there for such a short time and the charcoal/ash is a very poor conductor of heat.

All materials can be classified as either conductors or insulators.

A conductor is… a material that transfers heat well. Metals are good conductors of heat energy. This is because the atom particles are so well arranged that the first atoms to get hot vibrate a lot and bump the next, which bump the next etc.

Examples of heat conductors are… copper, platinum, gold

An insulator is… a material that does not transfer heat well

Examples of heat conductors are… cotton, vacuum, wood

CONVECTION: Convection is the cyclic movement of less dense hot particles that move up and more dense cold particles go down. Eventually all particles get heat energy from the element.Liquids are bad conductors of heat energy. However, a kettle of water can be heated to boiling point in minutes because a different method of heat transfer occurs. The water in contact with the heating element is heated by conduction. When the water is heated, it becomes more spread out, or less compact. Because the warm water is less dense than the cold water, it rises and the cold water sinks. As the warm water rises, it gives out heat to its surroundings and becomes denser. Eventually it starts to sink again and a steady stream of water is set up. The process is called convection and the circulating streams are called convection currents.