Energy

This page is linked with the other pages, Work and Power.  The three were to big a subject to put onto one page without it becoming too long therefore it was split into the three separate topics. 

This page is focusing on Energy and how it effects everything at every moment.  The different forms of energy and how they are all linked with each other and how through understanding 'conservation of energy' it is possible to find the chain of reactions energy goes through and aid engineers when they are designing or solving any problems. 

It is hard to actually describe energy, it is in everything that happens.  It is the capacity to do work.  To move something, heat something up, make a sound.  

It is measured in Joules, (J) the same as for work.

Types of Energy

It would be right to start at the beginning.  What forms of energy are there that we can list, without reading a book or watching a documentary to inform us.  It is surprising, when thought about, how much people know already. 

Light energy          

Given off from light bulbs to lightening, hot objects that are glowing are releasing energy as light and this takes the form of a wave.

Sound energy       

Created when an object creates waves in the atmosphere which are picked up by a receiver (the ear drum) and translated into sound.

Heat energy        

When one system is a different temperature to another there is a transference of energy in an attempt to balance the temperatures.

Work energy              

A transfer of energy when one point of application of a force moves through a distance.

Potential energy         

A stored energy with potential to change form and transfer its energy to another system.  ie a ball held in the air has potential energy due to the gravitational pull acting on it.  When the ball is released its potential energy transforms to other energy.

Kinetic energy         

Associated with motion, the ball in potential energy has kinetic energy when it is falling.  

Chemical energy     

Released during a chemical reaction.  Chemicals are stored potential energy when in-active.  Food can be placed under this category as it is stored energy that creates a chemical reaction in our bodies to release the energy.

Electric energy           

Created through electrical charges when current occurs.

Magnetic energy 

Two magnets brought together will either repel or attract each other.  The energy is transformed into kinetic energy

Radio energy     

Waves of energy that are picked up by a receiver and transformed into electrical signals within the receiver.  

Nuclear energy 

When nuclei split or fuse together they release energy.

Conservation of Energy

One of the main things that needs to be remembered is the rule about energy and the principle of the conservation of energy.

Energy does not disappear when a job is done, it changes into another form of energy release.  Coal is stored chemical energy that when processed and burnt in a power station is turned into heat energy, as this is used it changes to electrical energy.  This electrical energy is then used in the house to run equipment, which will turn the energy received into a different form of energy such as heat from the stove.

If you were to lift a 1kg box from the floor to a table of height 1m from the floor you would be using the energy gained from about 2.5 milligrams of sugar.  The box has also gained potential energy by being raised above the ground.  If the box were to fall the potential energy would transfer to kinetic energy on the way down.  When the box has hit the floor all the potential energy has gone and on impact the kinetic energy is released as heat energy along with air wave energy caused by the impact and sound wave on impact.  The heat created is made through friction between the surfaces. 

One of the best ways of considering how energy is transformed is the way a motor can turn mechanical energy into electrical energy.


Efficiency

Energy efficiency is measured as a ratio and defined as the ratio between the useful output energy to the input energy.  It is noted as ( n )  Efficiency no units and is often stated as a percentage.  A perfect machine would be 100% efficient but no machine is that good due to friction losses and heat losses.  

Example of calculating the efficiency:

Example

A machine exerts a force of 200 N in lifting a mass through a height of 6m.  If 2kJ of energy are supplied to it and the output is 1200J, what is the efficiency of the machine?

                                   n = 1200    =   0.6    or    60%
                                         2000

For a recap watch the video below and then move onto the Work and Power pages.