Why Do Our Fans Not Stop As Soon As You Turn It Off?

Fans are one of those humble, modern contraptions that many appreciate, especially during hot weather. While they are often mistaken for being able to cool down the room, they are actually “air benders”, bending the force of nature to their will in the truest sense of the word.

While they have been designed for human convenience, they have just one “flaw” – they never stop as soon as we turn them off. So, why do they not stop immediately? In this post, we will dive into the physics behind such behaviour.

How does a fan work?

No matter what kind of fan it is, whether it is a wall fan, a ceiling fan, or a standing fan, they usually are made up of a retention mechanism, which, combined with electrical wirings, is connected to a driving mechanism that consists of the blades, hub, and motor.

The mechanics behind fans are determined by the orientation and design of the blades. If you stop reading this article for a moment and take a look at your fan’s blades, you will realise that they are not completely flat. Rather, they are slightly arched. This design enables the blades to slice through the air, channelling wind towards the desired space.

This cutting and pushing motion is then multiplied through the high-speed revolutions that are powered by the motor, resulting in the constant blast of moving air. Fans are not used just for personal spaces. They are also used in a variety of cooling and ventilation needs, such as automobile radiators and computers.

Inertia in action

We all have learnt the law of physics that unless an external force is applied on a given body, it will continue to be in a state of motion or rest.

So, if you decide to stop pedalling your bicycle, you would, in the end, come to a stop due to the presence of frictional force. The same frictional force that enables your bicycle to move forward also robs some of the energy that you generate by pedalling. Hence, when you stop pedalling, it cancels away that generative force a little at a time until it is gone.

The same rule can be applied to fans. A rotating fan generates a huge amount of kinetic energy. When you turn off your fan, there is still a significant amount of kinetic energy left. Even if there is no electrical energy feeding the motion, the fan utilises the remaining kinetic energy. This motion is known as inertia.

Conservation of energy

It is said that the system’s total energy is always the same. It never decreases or increases; it always converts from one form to another.

Yet, we often hear about wasting energy, which can be referred to as energy that is converted into a form that cannot be utilised. The air resistance generated by the moving fan or the energy that is lost during the cycling process of overcoming frictional force are examples of wasted energy.

What happens if the fan stops immediately?

In theory, if the fan stops immediately, the remaining kinetic energy would have to be absorbed by the fan parts, mainly any of the mechanical fixtures, electrical wiring, and motor housing.

This immediate absorption of energy would lead to mechanical failure, as the kinetic energy is being transferred to the rest of the fan, causing it to break apart. In order to enable the fan to stop immediately, we would need to create a mechanism that is able to absorb the remaining kinetic energy and convert it into a useful form of energy, like the regenerative braking of an electric vehicle.

Conclusion

If we were to go ahead with the theory of creating an energy storage system in fans similar to that of an electric vehicle, that would mean having to incorporate another consumable, which is the brake. That means a more complex construction and the need for servicing, which would otherwise be a maintenance-free device.

Our world is full of devices and tools that function because of the law of physics. And if you have ever wondered such a question, you are not alone. If you are interested in finding out the physics behind other questions, such as why we do not sink, then be sure to contact Physics Tuition to sign up for our classes.