What is inertia?

We explain what inertia is and what types exist. Newton’s principle of inertia and everyday examples where inertia is experienced.

1. What is inertia?

Inertia is called in physics the resistance that bodies oppose to modify their state of motion or stillness , either to alter their speed, their course or to stop; although the term also applies to the modifications of your physical state.

A body thus requires force to overcome inertia to alter its trajectory , which otherwise would stick to the laws of the movement rectilinear uniform, or to start a movement, because otherwise remain idle. This, of course, considering that there is no rest or rectilinear and uniform movement in the universe , except based on a reference (observation) system. That is why it is preferred to speak of “relative rest.”

In this way, a body or system will have greater inertia insofar as it requires forces of greater intensity to modify its state of motion or to modify its physical state. These resistances are called “inertial forces” to change the state of movement or physical state, and they are fictitious forces that the observer perceives within the frame of reference.

2. Types of inertia

Thus, two types of inertia are distinguished in physics: mechanical and thermal.

• Mechanical inertia . Related to the difficulty of modifying movement and stillness, as we have explained above. It depends directly on the amount of mass of the body or system and the inertia tensioner.
• Thermal inertia . It measures the difficulty of a body or system to modify its temperature when it comes into contact with other objects or when it is heated directly. It depends on the heat capacity of the body or system.

However, mechanical inertia can be further subdivided into:

• Dynamic Inertia . It is presented by bodies in relative motion.
• Static inertia . It is presented by the bodies at relative rest.
• Rotational inertia . It is presented by bodies that exhibit rotational movement.
• Translational Inertia . It is linked to the total mass of the bodies.

3. Principle of inertia

The principle of inertia, known as Newton’s First Law , says that bodies will tend to maintain their state of rest or uniform rectilinear motion until an external force is applied to them capable of overcoming such resistance , which is referred to as above. We said, inertial force.

This principle of physics was formulated mathematically by Sir Isaac Newton in his work Philosophiae naturalis principia mathematica published in 1687, from the well-known Law of inertia of Galileo Galilei. And one of its fundamental concepts is the equivalence between the state of rest (speed 0) and that of rectilinear and uniform movement, since in both cases, if presented, they imply that no external force is acting on the body in question.

On the other hand, if we observe a body moving and losing speed gradually, we can attribute that loss of speed to the effect of friction forces that overcome its inertial principle.

4. Examples of inertia

Inertia can be verified and experienced through numerous examples. Some may be:

• Seatbelt . When a vehicle travels at a constant speed, its passengers share this speed with it. But if the driver suddenly stops the vehicle (or collides with another that prevents him from continuing his trajectory), the passengers will feel the thrust of the inertia that makes them keep their movement, throwing them forward. Then the safety belt intervenes, which overcomes inertia and interrupts its movement, preventing them from hitting with the windshield.
• Push a heavy object . When pushing a heavy object at rest, you feel the need to overcome inertia with the force of those who push. Once defeated, the object will move more easily, as it will be in motion; but initially it will resist moving.
• Quickly pull a tablecloth . In the typical act of the magicians, a tablecloth is thrown with objects on top, which remain in place due to inertial forces and do not move along with the cloth.
• Train braking . When trains seek to stop at the station, they take a while to do so, because the inertia they bring is so high that they require more braking space.
• The adobe of the constructions . The adobe is a usual construction material, especially in the most precarious homes, because it has a great thermal inertia: it resists heating, keeping the interior of the house cooler.