Work and Energy
This is a basic physics GCSE tutorial exploring in simple terms what work and energy are. Video tutorial to come.
What is work?
Newton's First Law of Motion tells us that in order to move something, you need to apply a force to it. When you apply a force to move something, you do work. How much work you do will vary depending on how quickly the object moves, the mass of the object, and how far you move it. You can calculate how much work is done moving an object with the following equation:
Work done = force x distance
W = F x s
- W refers to the amount of work done, reported in joules (or J),
- F refers to the force applied, measured in newtons (or N), and
- s refers to the distance the object has moved, measured in metres (or m).
From the above equation we know that one joule of work is done when a force of one newton causes an object to be displaced by one metre. Consequently, we can say that:
1 joule = 1 newton metre
What is energy?
Energy is what you use to do work. You can think of energy as a form of currency; you trade it in in order for work to be done. Without energy, you cannot do work. Energy is also reported in the unit joules or J.
In an ideal system, the amount of energy you use will be exactly the same as the amount needed to do the work. In reality some energy may be lost (or wasted) in the process. We'll discuss energy efficiency in a future tutorial.
There are many forms of energy
Energy comes in many different forms. We'll learn more about these in the future, but it's good to start to become familiar with some relevant terms:
- chemical energy is found in batteries, food, and chemicals;
- electrical energy is created by moving charges, or imbalances of charges (e.g. lightening);
- thermal energy is heat energy and is provided by your stove tops;
- nuclear energy is found in the nuclei of atoms;
- radiant energy is light energy and is provided by light bulbs;
- sound energy is produced by vibrating objects e.g. guitar strings, or the tissue of your vocal cords; and
- kinetic energy is the energy that a moving object has.
Energy can be dissipated, stored or transferred
Law of Conservation of Energy
Energy cannot be created from nothing, or destroyed; this is known as the law of the conservation of energy. In a way, this is quite intuitive; a bulb does not suddenly light up - it requires electrical energy to do so.
Similarly, a guitar string does not of its own accord suddenly start vibrating to produce sound - and neither do your vocal cords. Instead, we need to transfer or convert energy, in order to produce sound energy.
Transferring or Converting Energy
All around you energy is being transferred or converted from one form to another - you're even doing it right this very moment. Food that you ate a while ago was broken down in your body into little packages of chemical energy. Your body is now converting that energy into many different forms, including thermal and kinetic energy. This allows you to maintain a regular body temperature, and for your heart to continuously beat. Similarly, machines like cars need to convert and transfer energy in order to function (see below).
To ensure that energy is around when it's needed, we store it in handy and helpful places. For example, in the human body, energy can be stored in muscles in the form of chemical packages. When energy is stored, it is referred to as potential energy. This is because it is not actually doing anything, but it has the potential to do work. For example the energy stored in a car battery is referred to as potential chemical energy. The energy stored in a spring is referred to as elastic potential energy.
Work transfers Energy
In order for work to be done, energy must be transferred. For example, the person who pushes a block along a table does so by applying a force to the block. This transfers the chemical energy stored in the person's muscle to the block in the form of kinetic energy.
You'll notice that the block moves to the left at a faster rate than to the right. This is because a larger force is applied to the block (as depicted by the longer arrow). Does this make any difference to work and energy? Find out in this tutorial!