There are two types of energy: Potential energy (stored energy) and kinetic energy (moving energy). All forms of energy are stored in different ways in the energy sources that we use every day. These sources are divided into two groups, renewable energy and non-renewable energy. Renewable and non-renewable energy can be converted into secondary energy sources like electricity and hydrogen. Secondary sources of energy are used to store, move, and deliver energy in easily usable form. We have to use another energy source to make electricity or hydrogen, e.g. coals.

Energy is measured in joules (J). The work done, or energy used, during a certain time is called power. Power is measured in watts (W). A watt is the use of one joule of energy for one second. A watt is a small amount of energy, thus we measure power in units of 1000 watts for one hour, kilowatts for one hour. 

Jurassic katydid sings out after 165 million years - An exceptionally preserved fossil has allowed biologists to reconstruct the sound of an extinct bush cricket. So what did it sound like?

Today on New Scientist: 6 February 2012 - All today's stories on newscientist.com, including: the revolution will be tweeted and robotic walking stick lends users some balance

3D printer provides woman with a brand new jaw - Sculpting an entire replacement jawbone that's both fully functional and biocompatible is seen as a breakthrough for 3D printing

Patch of seagrass is world's oldest living organism - A 15-kilometre-long swathe of seagrass off the coast of Spain is at least 80,000 years old, making it the oldest known living organism on Earth