⇒ A machine is only useful if it can effectively convert one form of energy into another form of energy

• For example, cars - if you put petrol (i.e. chemical energy) into it, that can be converted into kinetic energy, allowing it to move

⇒ The total outputted energy from a machine is always equal to the total amount of energy put into the machine. However, not all of the output energy will be useful

• For example, only a fraction of a car's chemical energy is successfully converted into kinetic energy

⇒ Some of the input energy will be lost or wasted as other forms of energy other than purely useful energy (such as heat)

• For example, with the car, a lot of energy is wasted as heat and sound energy

⇒ The less energy that is wasted, the more efficient something is

⇒ The efficiency of a machine is defined as:

⇒ To determine how efficient something is, you must first find how much energy was originally supplied to it (i.e. the total energy input)

⇒ Then, you must find how much of that energy was output as useful energy

⇒ You can then work out how efficient the object was by dividing the smaller number by the large one, to produce a value for efficiency between 0 and 1

• Efficiency can also be displayed as a percentage by mutliplying the answer by 100 e.g. 0.7 x 100 = 70%

⇒ Also see our notes on:

• Moving and Storing Heat
• Melting and Boiling
• Conduction and Convection
• Heat Energy
• Saving Energy
• Energy Transfer
• Energy Transformation Diagrams
• Energy Sources
• Nuclear and Geothermal Energy
• Wind and Solar Energy
• Biomass and Wave Energy
• Hydroelectric and Pumped Storage