Work, Energy and Power

Dhristi JEE 2022-24

What are Work, Energy and Power?

Work Energy and Power are the most important terms used in Physics that the students learn in school early on. Work and energy are the two sides of a coin as both are interconnected to each other. Work is referred to as the displacement of an object when a force (push or pull) is applied to it while energy is referred to as the capacity to do the work. It exists in various forms like potential, kinetic, chemical, thermal, nuclear, electrical energy and so on. Power is the work done per unit of time. Studying work energy power is important in terms of both acquiring knowledge and getting higher marks in the exam.


Physics: Work and Energy 

When an object moves towards the direction of the force applied, then work is said to be done. But for work to be done energy is the most important thing as it is the ability to work. When work is done by animals or humans, they get the energy from food and when work is done by machines, they get energy from electricity or fuel. 


Work 

Work is done when a force produces some kind of motion. For example, when a man climbs a mountain, work is done because while climbing a mountain he is moving against the force of gravity. Hence, work depends upon two factors. They are: 

  • Magnitude of force

  • The direction in which the body moves due to the force applied.

Hence, work is measured by the product of displacement and force of a body along with its direction of the force. It is referred to as scalar quantity and the SI unit of work is Joule. 


The equation thus stands as:


Work = F * S


If a body is displaced by S while a Force F acts on it, in such a case


Work W = FS Cos (angle between the displacement and force)


One thing to note here is that force is said to work when it produces a motion in an object. For example, a man tries to move a wall but the wall does not move, hence the work done by the man is zero as there is no displacement produced. But he does lose energy because in his attempt to push the wall he stretches his muscles and thus feels tired. 


Thus, this shows that work doesn't need to be done whenever a force is applied to an object. Work is only done when the force applied can change the direction of the object or move it. 


Energy

The capacity of a man that allows him to do work is called energy. In simple words, energy is the ability to work. It is in scalar quantity and has only magnitude and no direction. energy can neither be created nor destroyed, it can only change in its form. Energy can be found in many things, and so there are many forms of energy. The most important types of energy are kinetic energy and potential energy. 


Kinetic energy refers to the energy of a body due to its movement or motion. It refers to the work that is required to accelerate a body of the given mass differentiating it from its velocity. While acceleration after the body gains energy, it maintains kinetic energy until its speed changes.


The formula of kinetic energy is –\[ \frac{1}{2}mv^{2}\] 


Hence from the formula given above, we can state:

1. The kinetic energy of a body gets doubled whenever its mass gets doubled.

2. If the mass of a body is halved, then the kinetic energy is also halved.

3. The kinetic energy of a mass increases by four times when the velocity doubles. 


Types of Energy 

Besides kinetic and potential energy, some other important types of energy are as follows: 

  1. Chemical energy: This refers to energy that is released by chemical substances on undergoing a chemical reaction which is further transformed into other substances.

  2. Mechanical energy: This is referred to as the sum of potential energy and kinetic energy. 

  3. Electrical energy: This energy is derived as a result of the movement that takes place between electrically charged particles. 

  4. Magnetic energy: A magnetic field is generated by electric currents. So, the energy that is the form of electrons is known as magnetic energy. 

  5. Nuclear energy: This is the energy that is released during the process of fission or fusion, especially when it is used to generate electricity. 

  6. Heat energy: This energy is produced as a result of the movement of atoms or molecules in solids, liquids, and gasses. 


Power Definition- Physics 

Work power or simply power is referred to as a physical concept that includes several meanings, depending on the context and the details available. Power can be defined as the rate of doing work. Power is the energy that is consumed per unit of time. It is present in scalar quantity as it does not have any direction. The SI unit of power is Joules/second and is termed as Watt. Watt refers to the power needed to do one Joule of work in a second. 


Difference Between Work and Power 

The differences between work and power are mentioned in the following table:

Work 

Power 

Work is referred to as the process of energy that is transferred to an object’s motion by applying force. It is generally represented as the product of displacement and force. 

Power is the amount of energy that is transferred in a unit of time. 

The SI unit of work is Joule (J). 

The SI unit of power is Watt (W). 

The formula for calculating the force is Work = Force * Displacement. 

The formula of calculating power = Work/Time. 

Work can be done in various other measures like kWh, MWh, GWh, and volt (eV). 

Energy can be measured in units like GW, MW, and kW. 

Work does not depend on time. 

Power depends on time. 


Difference Between Work and Energy 

Work 

Energy 

This is referred to as the activities carried out on a specific object that leads to some displacement. The relationship between displacement and the force components is parallel.  

This is referred to as a property of a given system, or in other words, the ability to do or carry out work. 

Energy is basically the result of all the work that has been performed. 

The concept of work had been devised in 1826. 

The word “energy” dates back to centuries; it was coined way back in 4BC. 

The formula for calculating this is Work = Force * Displacement. 

There are different equations that depend upon the various types of energy.  

Work is said to be positive given the force being applied is in the same direction as the displacement and is considered to be negative if the force is applied in the opposite direction of displacement.  

As energy is a scalar quantity, there is no direction component in its case. 


Difference Between Power and Energy

Power 

Energy 

This is the rate at which some kind of work is carried out or at which energy tends to be transmitted. 

This is the capacity to carry out work and is referred to as the power that tends to be integrated with time. 

Its SI unit is Watt (W) or joules/second. The symbol used to denote it is “P”. 

Its SI unit is either Joules (J) or watt-seconds. The symbol used to denote it is “W’. 


It is referred to as an instantaneous quantity. 

It is referred to as a time quantity. 

It is not possible to transform power from one given type to another. 

This keeps changing from one given form to another. 

It is not possible to store power. 

It is possible to store and conserve energy for future use/purposes. 

It is used in various mechanical applications, heat applications, etc. 

It is used in various activities like moving a car, heating a house, etc. 


Interesting Facts 

The word “energy” has its roots in Ancient Greece. It was derived from the Greek word “energia” which was coined by Aristotle in 384 BC. 


Food is considered to be a form of energy. It is a form of chemical energy which tends to be responsible for the growth, repair, and reproduction of living organisms. 


During the process of digestion, this energy is released into our bodies and is then converted into mechanical energy or heat. 

FAQs on Work, Energy and Power

1. Define Power in Physics.

Power can be defined as the rate at which work is done per unit of time. The SI unit of power is Watt (W) (which is calculated as joules per seconds). Earlier, power also referred to activity. It is a scalar quantity. The equation to measure power is P = W/t. The output power of any motor is referred to the product of a torque that a motor generates. The power that is involved in moving the motor is known as the product of traction force on its wheel and its velocity. 

2. What is the difference between work and energy?

Work

Energy

  • A parallel relationship exists between displacement and the force components.

  • Energy is the result of the task performed.

  • Work = force * distance

  • There are different equations of energy depending on its kind.

  • Work is positive when the force is applied in the same direction of displacement.

  • There is no direction component present in energy.

  • Work was conceptualized in 1826

  • The term ‘energy’ was coined before 4BC

  • Employment appears to be negative when the force applied is in the other way of displacement.

  • There is no direction component present in energy. 

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