viitekehiä

A viitekehiö, or reference frame, is a fundamental concept in physics and mathematics used to describe the position and motion of objects. It is essentially a coordinate system relative to which measurements are made. Without a defined viitekehiö, statements about position, velocity, or acceleration are ambiguous.

There are two main types of viitekehiö: inertial and non-inertial. An inertial viitekehiö is one in which Newton's first law of motion holds true; that is, an object will remain at rest or in uniform motion in a straight line unless acted upon by a net force. In a non-inertial viitekehiö, such as one that is accelerating or rotating, fictitious forces appear, which are not due to actual physical interactions but arise from the acceleration of the reference frame itself.

The choice of viitekehiö is often dictated by the problem being studied. For many everyday scenarios, a viitekehiö fixed to the Earth is sufficient. However, in celestial mechanics or relativistic physics, more complex or generalized viitekehiöt are necessary. The principle of relativity states that the laws of physics are the same in all inertial viitekehiöt. This means that no inertial viitekehiö is preferred over any other.