Dec 2016

Work, Energy and Power

December 27, 2016


Work, energy, and power are core concepts of physics. Below we look at these vital concepts in a little more detail.

What are Work, Energy, and Power?

Work is a simple concept- the transfer of energy. If an object gives energy to a second object, that first object performed work on the second object. You can also define it as the application of force over the distance. Both definitions are important to your understanding and will be explained in our physics tuition. Energy is therefore defined as the capacity to do work. Power is an expression of work done over time.

Energy and work share the same units of measurement [Joule] due to the fact they are so intrinsically linked. On the SI standard scale of units, power is represented in Watts, although under the English system it can be represented with Horsepower instead.

Is Every Application of Force ‘Work’?

No. Remember the key element of work is that displacement occurs. So, for example, simply exerting pressure on a non-moving object does not generate work, as there isn’t any displacement of the object. Also, remember that if there is displacement, but not caused by force, it is also not ‘work’. Vertical forces never cause horizontal displacements and vice versa. By this same principle, there is the concept of ‘negative work’- forces that act to hinder the displacement of the object. Friction is a classic example of negative work.

Some important definitions:

  • Work-energy principle: Change in kinetic energy = net work done on the object
  • Kinetic energy: Energy of movement
  • Potential energy: Stored energy

What More Should I Know About Energy?

While the two main types of energy cover all the energetic principles there are, there are of course many different forms of that energy. Solar energy covers microwaves, infrared, radio waves and UV light; and nuclear energy is the energy released in a nuclear reaction. Mechanical energy is an expression of movement, both in organic beings and machine;, while electric energy is the use/generation of electric forces. Chemical energy is the form of energy inherent when chemical bonds are either created or broken, and heat energy is represented by temperature changes. These different forms of energy all have their own properties and standard reactions.

What Equations Do I Need to Know?

  • The equation for power is as follows:

P= E/t

Where P=power, E=energy and t=a unit of time.

  • Work is calculated as follows:

W= Fd(cos(theta))

Where W=Work, F=force and d=displacement.

The cos(theta) angle refers to the direction the force is acting. Should you be given an angle to work with, it is critical you pay sharp attention to determining the correct angle for the equation. It is the angle between the force and the displacement vector only- not angles of incline or anything else. Remember that the fact that the work was done is at an angle to the horizontal displacement means that only some of that force directly causes the movement to the horizontal, and must be calculated accordingly.

Make sure you are up to speed with these basic principles of work, energy, and power, and physics will become considerably easier to understand too. You can also opt for JC physics tuition with us to ensure a guided learning journey in physics.

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