We explain what inertia is and what types exist. Newton's principle of inertia and everyday examples where inertia is experienced.
What is inertia?
In physics, inertia is called resistance that bodies oppose to modifying their state of movement or stillness whether to alter its speed, its course or to stop; although the term also applies to changes in your physical state.
A body like that requires a force that overcomes inertia to alter its trajectory which would otherwise adhere to the laws of uniform rectilinear motion, or to initiate a motion, since otherwise it would remain at rest. This, of course, considering that rest or rectilinear and uniform movement does not exist absolutely 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 to the extent that it requires greater intensity forces to modify its state of motion or to modify its physical state. “Inertial forces” are fictitious forces that the observer perceives within the frame of reference.
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 previously. It depends directly on the amount of mass of the body or system and the inertia tensor.
- Thermal inertia It measures the difficulty of a body or system to modify its temperature when coming into contact with other objects or when being 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 bodies at relative rest.
- Rotational inertia It is presented by bodies that exhibit rotary motion.
- Translational inertia It is linked to the total mass of the bodies.
Principle of inertia
The principle of inertia, known as Newton's First Law states that bodies will tend to maintain their state of rest or uniform rectilinear motion until an external force capable of overcoming said resistance is applied to them, which is called, as we previously said, inertial force.
This principle of physics was formulated mathematically by Sir Isaac Newton in his work Philosophiae naturalis principia mathematica published in 1687, based on Galileo Galilei's well-known Law of Inertia. 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 present, they imply that no external force is acting on the body in question.
On the other hand, if we observe a body move and gradually lose speed, we can attribute this loss of speed to the effect of friction forces that overcome its inertial principle.
Examples of inertia
Inertia can be verified and experienced through numerous examples. Some may be:
- The seat belt When a vehicle moves at a constant speed, its passengers share this speed with it. But if the driver suddenly stops the vehicle (or collides with another vehicle that prevents it from continuing its trajectory), the passengers will feel the push of inertia that makes them maintain the movement they had before the stop, throwing them forward. Then the seat belt intervenes, which overcomes the inertia and interrupts their movement, preventing them from hitting 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 pushing. Once defeated, the object will move more easily, since it will be in motion; but initially it will resist moving.
- Quickly pull a tablecloth In the typical act of magicians, a tablecloth is pulled with objects on top, which remain in place due to inertial forces and do not move with the cloth.
- Braking of trains When trains try 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 buildings Adobe is a common construction material, especially in the most precarious homes, because it has great thermal inertia: it resists heating, keeping the interior of the home cooler.
