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This is a basic physics GCSE tutorial exploring in simple terms what power is. Video tutorial to come.

Energy, work and time

We've learned that to move an object we need to do work on the object. When we do this, we transfer energy to the object.

As you would intuitively think, different amounts of energy are transferred depending on how quickly or slowly an object is moved. For example, a larger amount of energy is used to move the blue block to the left compared to to the right. We know this because the magnitude of the force to the left is greater than to the right (as depicted by a longer arrow), and work done = force x distance.

Similarly, it takes differing amounts of energy to bike a set distance slowly or fast. You'll also notice that you are more likely to be breathing quicker and harder if you cycle fast. Why is this?

Your body uses oxygen in a series of chemical reactions to convert the chemical energy stored in your fat and muscles into something you can actually use to do work. The faster you do work, the quicker your body needs to convert the stored chemical energy, and thus the quicker it needs to access oxygen - this is also why you breathe quicker when you run somewhere instead of walking there.

So if you use different amounts of energy to do a set amount of work, how do we differentiate between the different rates at which the work is done? We say that the quicker work is done, the more power is required.

What is power?

Power is a measure of how quickly work is done. Power can be calculated using the following equation:

Power = Work ÷ Time


P = W ÷ t


Watts is the same as joules/second

The unit we use to measure or discuss power is watts, named after the Scottish engineer James Watt. As you'll be able to tell from the equation above, 1 watt is actually the same as 1 joule per second (J/s).

1 watt = 1 joule/second

Knowing this helps you to remember that power is a way of measuring how fast or slow (i.e. the rate) at which energy is converted or transferred.

Work and Power

The quicker work is done, the more power is used to do it.

A racing car's engine is much more powerful than the engine found in a normal car. This is because it can burn through fuel at a quicker rate, producing usable energy at a faster rate. This allows the race car to cover a lap of a race course within a shorter period of time than a normal car. Interestingly, the race car will tend to burn through fuel at a disproportionately faster rate than the 'normal' car - which makes it more damaging to the environment.