ENERGY

ENERGY, in physics is the ability to do work. For example, the acceleration of a car or the lifting of a stone requires work. Work and energy are measured in the same units. People often confuse energy, power and force. Power is the rate at which work is done. Force is a push or a pull on an object or body. A force will deliver work as long as it moves the object. The amount of work will be determined by the strength of the force used and the distance over which the object moves. Energy associated with motion is called mechanical energy.

Forms of energy

Energy is one of the fundamental ideas in physics. The other is mass. Energy exists in several forms. One form of energy can change into another form in a process called coming from a fire reaches us as radiation. Objects close to the fire are warmed by infrared rays, a form of electromagnetic radiation. These objects gain energy in the form of heat. Light is also electromagnetic radiation and so is a form of energy. Other forms of energy are chemical energy, nuclear energy, electrical energy and mass.

All human life depends on the energy we receive from the sun in the form of radiation. The sun’s infrared radiation warms the earth and its light rays give plants the energy to grow. Plants store the sun’s energy as chemical energy in a process called photosynthesis. The food that plants make is the food on which all animals depend. Animals and human beings use the energy from food to drive their body processes and to move their muscles. The sun’s energy is also stored as chemical energy in oil, gas and coal. These fossil fuels are decay products of plants and organisms that lived millions of years ago. We burn these fuels to extract the energy in them. Burning converts the chemical energy in fuels into heat. Heat, in turn, can be changed into mechanical energy. For example, the burning of coal can power steam turbines that generate electricity in power stations. In a power station, chemical energy in coal is transformed into heat energy, which is itself transformed into mechanical energy. The mechanical energy delivered by the turbine is transformed by the generators into electrical energy.

NUCLEAR ENERGY is another form of energy, stored in the nuclei of atoms. Nuclear reactions, such as fission, release energy in the form of heat and radiations. Fission reactions produce the heat in nuclear reactors. Fusion reactions generate the intense heat in the core of the sun. In the outer layers of the sun, this heat is transformed into the radiation emitted by the sun in all directions. We receive only a tiny part of this radiation.

In fusion and fission reactions, the total mass of the end products of the reactions is slightly lower than the total mass before the reaction. A small fraction of matter has been converted into-energy. Scientists conclude that mass and energy are equivalent. All processes are governed by changes of energy from one into another.

Potential and kinetic energy

Mechanical energy is energy produced by movement, that is, the action of forces on objects. Kinetic energy is the energy an object processes because it moves. The word kinetic comes from the Greek word meaning to move. The kinetic energy of a body is proportional to its mass and to the square of its speed. So, a train moving at 80 kilometres an hour has four times the energy of a train travelling at 40 kilometres an hour. A standing train has no kinetic energy; all the kinetic energy it possessed while moving has been transformed into heat, generated by friction in the brakes that brought the train to a halt.

Potential energy is energy an object possesses because of its position or state. It represents work that has already been done and is sometimes called stored energy. If we lift a box from the floor on to a table, the potential energy of the box will be increased with the amount of work that was required to lift it on the table. Potential energy can be transformed into other forms of energy. If we push the box off the table, it will start falling and its potential energy is transformed into kinetic energy. When the box hits the floor, it causes vibrations in the floor and surrounding air. These vibrations heat up the floor and the air, so the kinetic energy of the box is transformed into heat energy.

Chemical energy is a form of potential energy, Molecules may store energy because of the potential energy of atoms. This potential energy is formed by the action of the forces that exist between atoms in molecules. During chemical reactions, atoms in molecules take up different positions, resulting in changes of the potential energies of these atoms. If the potential energy decreases, the reaction gives off energy as heat.

The conservation of energy

We have seen that during the time a box is falling from a table, its potential energy decrease while its kinetic energy increases. However, the sum of both forms of energy remains constant during the fall. Scientists express this constancy in a law which states that energy is conserved. The law of conservation of energy is not only valid for the falling box, but also for the entire universe. This law states that the total amount of energy in the universe is always the same.

The pendulum is an example of how energy is transformed from one into another, although the total energy is conserved. When a pendulum reaches the top of its swing, it was potential energy because of its position. As the pendulum swings through the lowest point of its swing, it has only kinetic energy. This energy becomes potential energy as the pendulum again reaches the top of its swing. The pendulum would swing back and forth forever if it were not for friction and the resistance of the air. But the energy used up in overcoming such friction is not lost. It is transformed into heat.

Because energy and matter are now known to be closely related, the conservation of energy can also include matter. Energy cannot be created or destroyed. But it may be developed from matter and turned into matter. For example, energy can be turned into matter in particle accelerators where new particles are created  when accelerated particles collide at extremely high speed,  E = mc².

Measuring energy

In the metric system, energy is measured in joules. One joules is the amount of work done by moving an object a distance of one metre against the opposition of one newton of force. Potential energy is measured by multiplying the weight of an object by the vertical distance it may fall before coming to rest. Kinetic energy is measured by the formula; kinetic energy = ½ mv², where m equals the mass of the object and v² equals the velocity of the object squared.

Power, measured in watts is the rate at which work is done. A machine is rated at one watt if it produces one joule per second.