reference frames

A frame of reference is a particular perspective from which the universe is observed. Specifically, in physics, it refers to a provided set of axes from which an observer can measure the position and motion of all points in a system, as well as the orientation of objects in it. There are two types of reference frames: inertial and non-inertial. An inertial frame of reference is defined as one in which Newton's first law holds true. That is, one in which a free particle travels in a straight line (or more generally a geodesic) at constant speed. In three dimensional Euclidean space, using Cartesian co-ordinates, this means that
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