Do you think that lying in the bed, you do not move? Concerning a floor and walls in the bedroom – yes. But you move as a point to circles in daily rotation of the earth. And still you fly around the sun together with the planet. And at night the speed of flight is higher, than in the afternoon, owing to bigger remoteness on the whole diameter.
In what the relativity of the movement consists
If in quiet weather the passenger who woke up in a cabin of the sailing yacht looks out in a window, he far will think not at once – the ship floats or lies in drift. Behind thick glass a monotonous sea smooth surface, above – a heavenly blue with motionless cloudlets. However, anyway the yacht will be in the movement. More than that – at once in several movements in relation to different reference systems. Even without taking space scales in attention, this person, being at rest concerning the case of the yacht, it appears in a condition of the movement of the mass of water which is rather surrounding it. It can be seen on a wake stream. But also in case the yacht drifts with the lowered sail, it moves with the water stream forming a sea current.
Thus, any body which is at rest concerning one body (reference system) at the same time is in a condition of the movement concerning other body (other reference system).
Principle of relativity of Galilei
Already medieval scientists thought of relativity of the movement, and in Renaissance these ideas gained the further development. "Why we do not feel rotation of Earth?" – thinkers asked a question. The accurate formulation on the basis of physical laws to the principle of relativity was given by Galileo Galilei. "For the objects taken by uniform motion – the scientist removed, is the last kind of does not exist and shows the action only on the things which are not taking part in it". However, this statement is valid only within laws of classical mechanics.
Relativity of a way, trajectory and speed
The passable way, trajectory and speed of a body or point will be also relative depending on the chosen reference system. Follow an example with the person going through cars. Its way for a certain period concerning structure will be equal to the distance passed by it own legs. The way concerning the earth will consist of distance which was passed by the train, and the distance which is directly passed by the person, and irrespective of to what party it went. The same with a speed. But here the speed of the movement of the person concerning the earth will be higher than the speed of the movement of the train – if the person goes on the movement of the train, and below – if it goes to the return to the movement the party. It is convenient to track relativity of a trajectory of a point on the example of the gayechka fixed on a rim of a bicycle wheel and holding a needle. Concerning a rim she will not be mobile. Concerning the case of the bicycle – it will be a circle trajectory. And concerning the earth the trajectory of this point will represent a continuous chain of semi-circles.