The best way to understand the fundamental differences between inertia and friction is with an example. So, we’ll lead with that.
Let’s say you are riding the bus home after a long day at work. The bus is crowded. You are standing, supporting yourself with the overhead rails. Suddenly, the driver slams on the brakes.
Your body lurches forward involuntarily – this is inertia. However, simultaneously, you intuitively tighten your grab on overhead rails, preventing yourself from smashing into the gentleman ahead of you. This is friction.
Over the course of this article, we will revise five (5) fundamental differences between inertia and friction.
Inertia and friction differ in their definitions
As from the example, inertia and friction entail two different experiences. Inertia is the tendency of a body to resist changes in its motion. Friction, on the other hand, is the force that opposes relative motion between two surfaces that are in contact.
Just to clarify, inertia doesn’t resist motion – it resists changes in motion.
Relationship with the body
Inertia is an intrinsic property of a body to resist changes in its motion. It comes from within the body itself. Friction, on the other hand, is a force. It acts on the body. It comes from the body’s interaction with its environment.
Simply put, friction is external whilst inertia is internal.
Unit of measurement
Inertia is measured in mass (kg) whilst friction is measured in newtons (N). Different quantities have different units of measurement.
Effect with environment
For the same body, inertia will remain the same regardless of the environment. Friction, on the other hand, depends on the surface in contact with the body.
Direction
Friction has direction as well as magnitude. Its direction is opposite to that of motion. Inertia on the other hand is independent of direction.
A quick summary
| Friction | Inertia |
| Force that opposes motion | Tendency to resist changes in motion |
| Measured in newtons (N) | Measured in mass (kg) |
| Depends on the environment | Independent of the environment |
| It has a direction | Independent on direction |
| Acquired. Depends on other factors | Intrinsic property of a body |
Conclusion
I will end this piece with another example.
Do you know this guy below? One of his “properties” is that he is muscular. Let’s say that is his inertia (pun intended). Also, depending on his mood, you may catch him smiling or frowning. It may be due to the time of day, environment, stress, etc. This is like friction.
As much as there is no correlation between The Rock’s facial expression and his ripped body – so it is with friction and inertia.
