![]() ![]() To identify an absolute inertial frame-the best approximation to suchĪ frame would be one in which the cosmic microwave background appears ![]() Of the orbits from the predictions of Newtonian mechanicsĭue to the orbital rotation of the Sun about the galactic center areįar too small to be measurable. To distant stars, is approximately inertial. Solar system), and whose coordinate axes are fixed with respect In the solar system, a reference frame whose origin is the center of the Sun (or, to be more exact, the center of mass of the In this case, the deviation is due to the Earth's orbital Orbits are measured to extremely high precision then they willĪgain be found to deviate very slightly from the predictions of Newtonian Is the center of the Earth (or, to be more exact, the center of mass of the Earth-Moon system), and whose coordinate axes are fixed with respect Objects around the Earth, a reference frame whose origin Is due to the fact that the Earth is rotating about a north-south axis, and its surface is thereforeĪccelerating towards this axis. Precision then it will be found to deviate slightly from the predictions If the trajectory of a projectile within such a frame is measured to high Respect to this surface is approximately inertial. If the first frame is an inertial frame then the second is not.Ī simple extension of the preceding argument allows us to conclude that anyįrame of reference that accelerates with respect to a given inertialįor most practical purposes, when studying the motions of objects close to theĮarth's surface, a reference frame that is fixed with Moves in a straight line with a constant speed in the first frame (i.e., if Is the instantaneous velocity of the second frame Respect to the first? In this case, it is not hard to see that Equation ( 2.11) Just as good as another as far as Newtonian mechanics is concerned.īut what happens if the second frame of reference accelerates with Motion is relative-hence, the name ``relativity'' for Einstein's theory. In fact, there is no absolute standard of rest, which implies that all However, Einstein showed that this is not the case. Newton thought that one of these inertial frames was special andĭefined an absolute standard of rest: that is, a static object in this frame was in a state of absolute rest. We conclude that the second frame of reference is also an inertial frame.Ī simple extension of the preceding argument allows us to conclude that thereĮxists an infinite number of different inertial frames moving with constant Moves in a (different) straight line with a (different) constant speed Object moves in a straight line with a constant speed in our original Object in the two reference frames satisfyĪccording to Equations ( 2.7) and ( 2.11), if an ![]() It is evident, from Figure 2.1, that at any given time, (See Figure 2.1.) Suppose that the position vector To the corresponding axes in the first frame, thatĪnd, finally, that the origins of the two frames instantaneously coincide at We can suppose that the Cartesian axes in the second frame are parallel With respect to the origin of the coordinate system, as a function of time,Ĭonsider a second frame of reference moving with some Of a point object can now be specified by giving its position vector, Set up a Cartesian coordinate system in this frame. Suppose that we have found an inertial frame of reference. Net external force moves in a straight line with constant speed. Thus, an inertial frame of reference is one in which a point object subject to zero Indeed, we can think of Newton'sįirst law as the definition of an inertial frame. However, this is only true in special frames of reference called inertial frames. In a straight line with a constant speed (i.e., it does not accelerate). Newton's first law of motion essentially states that a point object Next: Newton's second law of Up: Newtonian mechanics Previous: Newton's laws of motion ![]()
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