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CSEC Physics: Energy

Energy is defined as the ability to do work. Work is force applied over distance, or the distance moved in the direction of application of a certain force. It is calculated like this:

W= F×d

where:

F= force applied

d= displacement in the direction of the force being applied


Energy and work are both measured in Joules (J). There are many different forms of energy. Forms of energy can be divided into potential and kinetic energy.


Potential Energy

This is essentially stored energy, or energy that an object has by virtue of its position or state of being.


Kinetic Energy

This is the energy of movement, or the energy an object has due to being in motion.


We will discuss more details about kinetic and potential energy in a later lesson.


Gravitational energy

Gravitational energy is potential energy experienced by one object in relation to another massive object due to an attraction known as gravity.


Elastic energy

Elastic energy is potential energy stored by an object simply due to a temporary strain on it. That is, certain objects, when work is performed upon them, they experience elastic deformation, and have the tendency to return to their original shape/form. Think of a spring- when it is extended, it stores the energy as elastic energy. When you stop applying force to extend it, it springs straight back to its original shape, converting the elastic energy to kinetic energy.


Chemical energy

Chemical energy is potential energy possessed by a certain object or substance based on the bonds between atoms and within molecules (that change during chemical reactions to release that potential energy).


Electrical energy

Electrical energy is energy resulting from the movement of electrons through a conductive medium.


Magnetic energy

This is the energy of a magnetic field. A definite amount of energy is stored in all permanent magnets, so when a magnet attracts a piece of metal, it does work by using some of the magnetic energy to move the metal.


Electromagnetic energy

Electromagnetic energy, or radiant energy, is a form of energy emitted or reflected as waves by certain objects that can travel through empty space, including things like microwaves, gamma rays, visible light and ultraviolet light. These waves are capable or transferring energy to other objects, and are composed of oscillating electric and magnetic fields (hence the name electromagnetic energy).


Thermal energy

This is the energy of heat based on the motion (kinetic energy) of the particles in a substance. All matter is made up of particles that are constantly moving; therefore all matter has kinetic energy. At higher temperatures, particles move faster, thus having more kinetic energy and greater thermal energy.


Nuclear energy

This is the potential energy stored within the nucleus of an atom. The nucleus of an atom is extremely dense and held together by an immense amount of force. Thus, when a nucleus is split through nuclear fission, or joined to another through nuclear fusion, a massive amount of energy (usually heat) is released. This is the basis of nuclear power plants (use the fission of uranium to generate electrical energy) and even how the sun produces energy (fuses hydrogen nuclei to form larger helium nuclei releasing intense heat in the process).


Sound energy

This is energy produced during the vibration of an object. Sound energy travels as vibrations (or oscillatory waves) through fluids like air and water. So, when you strum a guitar, the strings vibrate and displace the air, causing sound.


So, these several forms of energy are involved in many of the energy transformations in everyday life.

When energy changes forms, the total amount of energy is conserved. However, the amount of useful energy is almost always less than the total amount of energy For example, if we consider an electric fan:



It receives an energy input of electrical energy. A good portion of it is converted to the kinetic/mechanical energy of the fan blades. However, because it causes vibrations in the air, some energy is converted into unwanted sound energy. Some energy is lost as thermal/heat energy. (You should note that thermal energy is always a by-product of energy transformation)




The ratio of useful energy to total energy input is known as the energy efficiency of the conversion. So, in the above conversion, the useful energy is the kinetic energy of the fan blades (because that is what moves the air). If we said, for instance, that 240 J of electrical energy is the input for the fan, and that the blades have a kinetic energy of 180 J for every 240 J of input, then we can express the efficiency of the fan like this:


Efficiency = Useful energy output/Total energy input

= 180 J/240 J

= 75%


You are probably aware that you use a lot of electricity. The average person uses about 25200000000 J of electricity yearly (and that's a conservative estimate). So, it is important that the way we source electricity doesn't harm the environment. About 63% of the world's electricity is produced using fossil fuels, which release greenhouse gases when burned to release their sweet chemical energy. You know the whole greenhouse effect and global warming story already, so you should already know why renewable energy is important.

Thus, we must use renewable energy sources such as:


Hydroelectricity

Hydroelectric plants convert the energy in flowing water into electricity. The most common form of hydroelectricity uses a dam on a river to retain a large reservoir of water. Water is directed through turbines to generate power.


Geothermal energy

The Earth’s core, 4,000 miles below the surface, can reach temperatures of 9000° F. This heat—geothermal energy—flows outward from the core, heating the surrounding area, which can form underground reservoirs of hot water and steam. These reservoirs can be tapped for a variety of uses, such as to generate electricity or heat buildings. By using geothermal heat pumps (GHPs), we can even take advantage of the shallow ground’s stable temperature for heating and cooling buildings. The geothermal energy potential in the uppermost 6 miles of the Earth’s crust amounts to 50,000 times the energy of all oil and gas resources in the world.

Geothermal power plants access the underground steam or hot water from wells drilled a mile or more into the earth. The steam or hot water is piped up from the well to drive a conventional steam turbine, which powers an electric generator.


Tidal energy

This is essentially the same as hydroelectricity, however it instead uses the predictable movements of the tides to move turbines and paddles to produce electricity.


Solar energy

The sun is basically an infinite source of energy, so it makes sense to use it to produce electricity. Solar electricity or photovoltaic (PV) technology converts sunlight directly into electricity. Although many types of solar electric systems are available today, they all consist of basically three main items: modules that convert sunlight into electricity; inverters that convert that electricity into alternating current so it can be used by most household appliances; and possibly or sometimes batteries that store excess electricity produced by the system.


Wind energy

Wind energy (the movement of air currents) is harnessed using wind turbines which spin around a central hub and a shaft which spins a generator to produce electricity.





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