Acceleration Different:

Einstein observed something exceptional about accelerating reference frames as compared with those which are not accelerating. This difference is noticeable when we consider the case of a spectator who is enclosed in a chamber which is fully opaque and sealed.

Assume that you are in a space ship in which the windows are cover up and the radar and navigational equipment have been positioned on standby. There is no manner for you to inspect the surrounding atmosphere and establish where you are, how rapid you are moving, or in which direction you are moving. Though, you can tell whether or not the ship is accelerating. This is so since acceleration always generates a force on objects within the ship.

Whenever the ship's engines are fired and the vessel increases speed in the forward direction, all the objects in the ship (involving your body) recognize a force directed backward. When the ship's retro rockets are fired therefore the ship slows down (i.e., decelerates), the whole thing in the ship recognizes a force directed forward. When rockets on the side of the ship are fired therefore the ship changes direction without varying its speed, this too is a type of acceleration and will cause everything within the ship to recognize a sideways force. Some illustrations are demonstrated in figure shown below.

Figure: Whenever a vessel in deep space is not accelerating, there is no force on the objects within. Whenever the ship accelerates, there is always a force on the objects within.

The higher the acceleration or alter in velocity, to which the space ship is subjected, the higher is the force on every object within it. When m is the mass of an object in the ship (i.e., in kilograms) and a is the acceleration of the ship (i.e., in meters per second per second), then the force F (in newtons) is their product as follows:

F = ma

This is one of the most familiar formulas in physics.

This acceleration force takes place even if the ship's windows are enclosed up, the radar is switched off, and the navigational equipment is positioned on standby. There is no manner the force can be blocked out. In this manner, Einstein explained, it is possible for interstellar explorers to establish whether or not their ship is accelerating. Not only this, though they can compute the magnitude of the acceleration and also its direction. Whenever it comes to acceleration, there is, in certain logic, absolute reference frames in the cosmos.