conservation of energy

The simplest definition of energy is “the capacity to do work”. Energy is how things change and move. It’s everywhere around us and takes all sorts of forms. It takes energy to cook food, to drive to school and to jump in the air. Energy is required for the evolution of life forms on Earth. There are various forms of energy – heat, electrical, chemical, nuclear, etc.

What is the Law of Conservation of Energy?

The Law of Conservation of Energy states that energy can neither be created nor be destroyed, but may be changed from one of its forms to another. If you take all forms of energy into account, the total energy of an isolated system always remains constant.

This means in an isolated system such as the universe, if there is a loss of energy in some part of it, there must be a gain of an equal amount of energy in some other part of the universe. Energy changes form, but the total amount of energy in the universe stays the same.

When we use energy, it doesn’t disappear but gets changed from one form of energy into another. For example, a car engine burns gasoline and it converts the chemical energy in gasoline into mechanical energy. Another good example of the law of conservation of energy is solar cells changing radiant energy into electrical energy.

When we observe energy conversions in our daily life, it may seem that energy constantly disappears. For example, if we kick a soccer ball along the ground, we give kinetic energy to the ball. It will roll for a while but eventually stop. Let us consider what might have happened to the ball’s kinetic energy. As the ball rolls, it rubs against the ground. Some kinetic energy changes into heat as a result of friction. Some of the ball’s energy also changes into sound energy that you can hear as the ball moves. Although the ball loses kinetic energy, the overall amount of energy in the universe does not decrease. The ball loses energy but this energy is transferred to other parts of the universe. Energy is conserved; it can neither be created nor destroyed. Although in many instances it may appear that energy is gained or lost, it is really only changed in form.

Conservation of energy is a balance of energy in the universe. When a soccer ball is kicked, a certain amount of energy is transferred by the kick. The ball gains an equal amount of energy, mostly in the form of kinetic energy. However, the ball’s kinetic energy decreases as some of that energy is converted into sound energy and heat from the friction between the ball and the ground. According to the Law of Conservation of Energy, the amount of energy that a soccer player gives to the ball by kicking is equal to the energy the ball gains. In turn, the energy the ball loses is equal to the amount of energy that is transferred to the universe as sound energy and heat as the ball slows down.

Different forms of energy

Broadly, energy can be categorized into two broad categories:

• Kinetic energy is the energy of moving objects
• Potential energy is the energy that is stored

Energy can take a number of different forms. Here are some examples

• Chemical – Chemical energy comes from atoms and molecules and how they interact.
• Electrical – Electrical energy is generated by the movement of electrons
• Gravitational – Large objects such as the Earth and the Sun create gravity and gravitational energy.
• Heat – Heat energy is also called thermal energy. It comes from molecules of different temperatures interacting.
• Light – Light is called radiant energy. The Earth gets a lot of its energy from the light of the Sun.
• Motion – Anything that is moving has energy. This is also called kinetic energy.
• Nuclear – Huge amounts of nuclear energy can be generated by splitting atoms.
• Potential – Potential energy is energy that is stored. One example of this is a spring that is pressed all the way down. Another example is a book sitting high on a shelf.

The standard unit of measure for energy is the Joule which is abbreviated as J. Some other units of measuring energy are used – kilowatt-hours, calories, Newton-meters, therms, and foot-pounds.

 

Energy Transfers

Energy transfer takes place when energy moves from one place to another. Energy can move from one object to another like when the energy from your moving foot is transferred to a soccer ball or energy can change from one form to another. When the energy in a battery is used to power an electronic device, chemical energy is transformed into electrical energy, which moves along wires. Energy can be transferred through light, sound, and heat.

Energy can be transferred as light - Light energy is the only form of energy we can see. Light from the sun helps plants grow and makes food for us to enjoy. The sun’s energy also powers solar cells, which can be used to create electricity.

Energy can be transferred as sound – Loud concerts, marching bands or loud music coming through speakers sometimes produce enough energy that you can feel the vibrations in your body. Sound energy is transferred when a sound wave travels from its source like a drum to another object. If the sound is loud enough, the waves will create very intense vibrations that you can feel in your chest.

Energy can be transferred as heat – When you sit by a campfire, you can feel the heat warm your body. Heat can move from warm objects to cooler objects.

Some commonplace examples of the law of conservation of energy are as below

• When a moving car hits a parked car and causes the parked car to move, energy is transferred from the moving car to the parked car.
• The green plants use sunlight to carry out the photosynthesis process. It allows them to store the energy in their cells. In this process, the light energy is converted into chemical energy which they use for their growth and nourishment.
• When we switch on the fan, the electrical energy gets converted into mechanical energy.
• In thermal power stations, the heat energy is converted to electrical energy. The heat, however, is generated from the combustion of fossil fuel, which is a transformation of chemical energy into heat energy.
• When you stop a ball from rolling on the floor, it may seem like there’s no conversion of energy, but in reality, you absorb the kinetic energy of the ball and turn it into heat potential energy.
• Even when you are pushing a chair to move it from its static position, you are using the potential energy stored in your body to do the task. At first, your potential energy gets transferred to the chair. Then it is converted into kinetic energy, which finally makes the chair move from its position.
• Water can produce electricity. The water falls down from the sky, converting potential energy to kinetic energy. This energy is then used to rotate the turbine of a generator to produce electricity. In this process, the potential energy of water in a dam can be turned into kinetic energy which can then become electric energy.

One interesting consequence of the law of conservation of energy is that it means perpetual motion machines of the first kind are not possible. In other words, a system must have an external power supply to continuously deliver unlimited energy to its surroundings.