According to the precepts of physics, all movement is the variation of the position of an object over a period of time. This variation is necessarily relative, since it occurs with respect to a reference point or referential system that accounts for the displacement produced.
Thus, it is possible that two or more observers have different appraisals of the moving object , according to their respective locations and points of reference, or that considering one we only calculate the movement of the object as if it were absolute. That is why we can distinguish between these two types of movement: the relative and the absolute .
- The relative movement refers to the one that presents an object with respect to a mobile point of reference. Therefore, the amount or dimension of the movement will be established according to the location also variable of the observer.
- The absolute movement , however, refers to an independent movement of its reference points, considering absolute and eternal. It is, obviously, a method of abstraction, useful to think a movement from a fixed reference system.
However, it should be emphasized that there is nothing that is in absolute rest in the universe, so all movements are always relative.
Examples of relative movement
- Walking from one car to another in a moving train: we move backwards in an advancing train, therefore we do not really regress, neither do we advance either, or both at the same time.
- Go down an escalator that goes up: we go down in something that in turn goes up, so we neither go down nor go up at all, or both at the same time.
- Walking on the deck of a sailing boat: we could walk in circles and at the same time move in a straight line.
- To fly in an airplane against the earth’s rotation: the earth turns and we with it, but at the same time we go in the opposite direction.
- Running next to a moving car: if we reached the same speed as the car, it would seem to be stopped.
- Dropping an object on an ascending plane: the object could fall and rise at the same time, depending on whether we see it inside the plane or from outside.
- A passenger on the platform of the subway: you can see the train move through the station, while one on board the train sees the platforms happen as if they moved.
- Running on a moving conveyor belt: if the belt advances, we would be advancing on something that in turn advances, but if it recedes, we could appear at rest.
- A boat advances on a river in favor of its channel: it will move at a higher speed than if it were against the channel. From the launch, however, there will be no major difference.
- A space rocket moves away from the earth that moves away in its orbit: seen from the earth is the rocket that moves, seen from the rocket is the earth that moves away, but seen from the sun both objects move.
Examples of absolute movement
- The sun seen from the earth: even though we are the ones who move around us, the movement of the sun is practically absolute in our daily life.
- The repose of objects: if we leave something on the ground in a totally controlled environment, we will see it remain in absolute rest, although we know that the tectonic plate underneath is constantly moving.
- The advance of a motorcyclist: seen from a pedestrian waiting for the traffic light, is an absolute movement that contrasts with its apparent stillness.
- The movement of a bullet: it is the bullet that we consider moving toward its destination, even if it is in motion (and it is better) or if the gun in turn moves as a result of the recoil of the explosion.
- A home run in baseball: the ball is considered moving when leaving the stadium, without considering the rotation of the ground at all.
- An object that falls: gravity exerts an absolute movement on the cup that we stumble unintentionally and rushes full of coffee to the floor of the kitchen. It does not matter that in relation to the sun the cup is moving in another direction to the one that falls.
- The wind on deck: we usually selectively ignore the wind or the displacement of the ship when we travel, although both the boat and the air are moving (in the same direction or in an opposite direction).
- A space rocket that takes off: seen by those who are left behind in the earth, it is the rocket that moves, although it is part of the orbital displacement of our planet (at least until it leaves it completely).
- The terrestrial translation: contemplating it only from the sun, without caring that this in turn revolves around the center of the galaxy.
- A car on the highway: observed from the point of view of the policeman who measures the speed, even if he is walking towards his motorcycle.