Power vs Work
Power and work are two very important concepts discussed in mechanics. Power describes the rate of energy transfer. Work describes the amount of energy transferred. Both of these concepts are very important in fields such as engineering, physics, thermodynamics and even human biology. In this article, we are going to discuss what work and power are, their definitions, similarities between work and power, their applications, and finally the difference between power and work.
In physics, work is defined as the amount of energy transferred by a force acting through a distance. Work is a scalar quantity, which means there is only magnitude for work, and direction is not present. Consider an object being dragged on a rough surface. There is friction acting on the object. For given points A and B, infinite number of paths exist between them; therefore, there are infinitely many routes to take the box from A to B. If the distance the box travels when it is taken on a certain path is x, work done by friction (F) on the box is –F x, considering only the scalar values. Different paths have different x values. Therefore, work done is different. It can be proved that work is dependent on the path taken, which means work is a path function. For a conservative force field, the work done can be taken as a state function. The SI unit of work is Joule, named in honor of the English physicist James Joule. The CGS unit for work is erg. Other units are foot-pound, foot-poundal and liter-atmosphere. In thermodynamics, work is usually referred as the pressure work because the internal or external pressure is the force generator that does the work. In a constant pressure situation, the work done can be taken as P.ΔV, where P is the pressure and ΔV is the change in volume.
To understand the concept of power properly, one must first have an understanding of the concept of energy. Energy is a non-intuitive concept. The term “energy” is derived from the Greek word “energeia”, which means operation or activity. In this sense energy is the mechanism behind an activity. Energy is not a directly observable quantity. But it can be calculated by measuring external properties. Energy can be found in many forms. Kinetic energy, thermal energy and potential energy are to name a few. Energy is measured in joule. Power is defined as the rate of energy. This rate can be a conversion or a creation of energy. When nuclear reactions are not present, power is always the rate of conversion of energy. Energy is measured in watt. 1 watt is equal to 1 joule per second. In electrical systems, a unit derived from watt is used to measure the amount of energy. This unit is kilowatt-hour.
What is the difference between Power and Work?
• Work represents the amount of energy transferred when doing something. Power represents how fast the energy was transferred.
• Work is measured in joules whereas power is measured in watts.
• An object can have a value for the power without doing any work. If the object does any work the value of the power cannot be zero.