P1aL4 Types of Energy and Changes

Key Words

Chemical Energy - energy that is transferred by chemical reactions.

Conservation of Energy - Energy can not be created nor destroyed; it's turned from one form to another.

Electrical energy - energy transferred in the form of electricity

Heat energy - energy flowing from a hot object to a cold object.

Joules - unit of energy (named after James Prescott Joule (1818 - 1879).

Kinetic Energy - energy contained in moving objects.

Potential energy - energy contained in an object raised off the ground (gravitational P.E.) or in a stretched spring (elastic P.E.).

Stored Energy - energy that can be stored and released when needed.

Grade E

Fuels contain chemical energy which is released when the fuels are burned.

Moving objects have kinetic energy.

Potential energy is contained in any object that can fall (gravitational potential energy) or anything that is squashed or stretched so that it will spring back (elastic potential energy).

There are other forms of energy, such as electrical, radio waves, etc.

Energy transfers involve moving energy from one place to another.  Energy transformations involve turning energy from one form to another (like electricity into kinetic energy).

Grade C

Energy is measured in Joules.  A joule is not a very big unit.  When you walk 1 km to school, you use about 300 000 J.  Our bodies give off heat at a rate of 100 J every second.

Some forms of energy can be stored:

• Chemical energy in a fuel;
• Kinetic energy in a spinning wheel;
• Elastic energy in a coiled up spring.

Some energy cannot be stored:

• Electricity (has to be stored as chemical energy in a battery
• Light;
• Heat (has to be stored as internal energy (e.g. in the hot bricks of a night storage heater).

A lot of energy gets wasted as heat.  A 100 watt bulb gives off about 2 J/s of light, and 98 J/s of heat.  Sometimes the waste heat can be used to do something useful.  However it mostly goes to heat up the environment.

Grade A

Lots of energy comes from the Sun, about 2 × 10¹⁷ J every second.  45 minutes would satisfy all the world's energy needs for a year.  The Sun's energy is used in:

• Direct heat;
• Energy for photosynthesis;
• Energy to drive the weather, including wind and rain;
• The carbon cycle.

Renewable energy mostly comes from the Sun.

The Sun works by fusing hydrogen nuclei to form helium, which gives out a huge amount of energy.  The mass of the helium made is very slightly less than the mass of the hydrogen.  Some of the mass has been turned into energy.  We can recreate the conditions in a hydrogen bomb, but scientists have not yet managed to control fusion to give out energy for a power station.