Physics 1a

Energy can change from one form into other forms and transferred from one place to another but cannot be created or destroyed. Useful energy is energy in the place we want it and in the form we need it. Waste energy is energy that is not useful. Both useful and waste energy end up being transferred to the surroundings which become warmer. Energy is measured in joules. Heat tends to flow away from a hotter object to its coolest surroundings.Heat is transferred in three different ways: Radiation, Conduction and Convection.Thermal radiation is the transfer of heat energy by electromagnetic waves. Convection and conduction involve the transfer of energy by particles. Metals are good conductors because they contain lots of electrons that can move about freely inside the metal. Conduction of heat - Occurs in solids and Convection of heat - Liquids and gases only. Conduction of heat is the process where vibrating particles pass on their extra kinetic energy to particles next to it. Metals conduct heat better than plastic or wood because of their free electrons. Convection occurs when the more energetic particles move from the hotter region to the cooler region and take their heat energy with them. Convection currents are all about changes in density.

Efficiency is a measure of how much useful energy you get out of an object from the energy you put in to it.

Conduction

• Metals are the best conductors because they have free electrons.
• Particles vibrate and pass on their energy. Free electrons move about passing on energy.
• solids that do not let heat travel through them are called insulators.

Convection

• Hot air/liquid rise and cold air/liquid sinks.
• As the particles move away from the heat source they loose their energy and move together becoming more dense.
• Particles gain energy and spread apart causing the liquid or gas to become less dense.
• Less dense rises and more dense sinks.

Radiation

• Shiny light surfaces are poor absorbers but good reflectors.
• The hotter an object is the more infra red radiation is given out.
• Dark mat surfaces emit (give out) the most radiation.