Inerciárendszer

Inerciárendszer, often translated as inertial frame of reference, is a fundamental concept in classical mechanics and relativity. It refers to a coordinate system in which Newton's first law of motion, also known as the law of inertia, holds true. This means that an object at rest will stay at rest, and an object in motion will continue in motion with constant velocity (meaning constant speed and direction), unless acted upon by a net external force.

In a true inertial frame, there are no fictitious forces. Fictitious forces, such as the centrifugal force or Coriolis force, appear in non-inertial frames of reference – those that are accelerating. For instance, if you are in a car that is accelerating or turning, you experience forces that seem to push you around, but these are not due to actual physical forces acting on you from external objects. They are artifacts of your accelerating frame of reference.

While a perfectly inertial frame of reference is an idealization, it is a practical and immensely useful concept. For many everyday purposes, frames of reference that are stationary relative to the Earth's surface can be approximated as inertial, although strictly speaking, the Earth is rotating and orbiting the Sun, making it a non-inertial frame. In physics, the Sun's center or the center of the galaxy are often used as approximations for inertial frames in astronomical calculations. The principle of relativity states that the laws of physics are the same in all inertial frames of reference.