What is the relativity of motion

When calm weather awakened in the passenger cabin sailing yacht to look out the window, it is not immediately realize - or sailing boat is drifting.Behind thick glass monotonous expanse of the sea, above - Heavenly Blue with fixed clouds.However, in any case, the yacht will be in motion.And more than that - just a few movements with respect to the different frames of reference.Even without taking into account the cosmic scale, this person is at rest with respect to the hull, it is in a state of motion relative to the surrounding body of water.This can be seen by the jet wake.But if the boat is drifting with a flat sail, it moves with the water
flow, forming sea current.

Thus, any body at rest with respect to one body (frame) at the same time is in a state of motion relative to the other body (the other frame of reference).

Galilean relativity principle

of relative motion medieval scholars had thought, and the Renaissance these ideas were further developed."Why do not we feel the rotation of the earth?" - Wondered thinkers.A clear statement on the basis of physical laws the principle of relativity gave Galileo Galilei."For the items seized by uniform movement - he brought a scientist - the latter would not exist and exert its effect only on things that do not take part in it."However, this statement is valid only within the laws of classical mechanics.

relative path, trajectory and speed

Passed the path, the trajectory and speed of the body or points will also be relative, depending on the selected frame.Take the example of a man going through cars.His way for a certain period of time the composition is to be covered by it own feet distance.The way with respect to earth will consist of the distance that the train has passed, and directly traveled distance man, and, no matter in which direction it came.With the same speed.But here the speed of the person with respect to earth is greater than the speed of the train - if a person is on the movement of trains, and lower - if it goes in the opposite movement direction.

convenient point relative to the path seen in the Gadget, attached to the rim of a bicycle wheel and hold the needle.Regarding the rim it will be fixed.Bicycle relative to the housing - this is a circle trajectory.A relative of the earth trajectory of this point will be of a continuous chain of semicircles.