Work and Energy

Priyanka Devan
Updated on

Energy is an important word which we use in our everyday life. Or in other words, we can say it is the ability of something to do work.  Even though it is often used loosely, it has a specific physical meaning. Basically, it is not a material substance. Energy can be stored and measured in many forms.  We often hear people talking about energy conservation. We all know that energy is never destroyed and it is just transferred from one form to another. Some forms of energy are less useful to us than others. Low-level heat energy is the best example. It is more likely to talk about the consumption or extraction of energy resources like coal, oil, and wind, than the consumption of energy itself.

Kinetic energy is a form of energy, that an object or a particle has by reason of its motion. If work transfers energy which is done on an object by applying a net force, the object speeds up and therefore gains kinetic energy. A speeding bullet has a measurable amount of energy associated with it. This is known as kinetic energy.


 Bullet gained this energy due to the work done on it. It is by a charge of gunpowder which lost some chemical potential energy during the process.

 A hot cup of coffee has a measurable amount of thermal energy. This is acquired through work done by a microwave oven. This will take electrical energy from the electrical grid.

Whenever there is work done to move energy from one form to another, there is always some loss of other forms of energy. That is heat and sound. Let’s consider an example. A traditional light bulb is only about 3% efficient. This converts electrical energy to visible light. But in the case of a human being, it is about 25% efficient at converting chemical energy from food into work.


Joule is the standard unit used to measure energy and work done and it is denoted by the letter J. One joule is the energy transferred when a force of 1 Newton is applied to an object and moves it through a distance of 1 meter.

A calorie is another unit of energy. The amount of energy in an item of food is often written in Calories on the back of the packet. A 60-gram chocolate bar for example contains about 280 Calories of energy. One Calorie is the amount of energy required, to raise 1 kg of water by 1^∘degrees Celsius. This is equal to 4184 joules per Calorie. So one chocolate bar has 1.17 million joules or 1.17 MJ of stored energy. That contains a lot of joules.

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