![]() The faster a sound wave travels, the more distance it will cover in the same period of time. In equation form, this is speed = distance/time Since the speed of a wave is defined as the distance that a point on a wave (such as a compression or a rarefaction) travels per unit of time, it is often expressed in units of meters/second (abbreviated m/s). Always be cautious to distinguish between the two often-confused quantities of speed ( how fast.) and frequency ( how often.). While frequency refers to the number of vibrations that an individual particle makes per unit of time, speed refers to the distance that the disturbance travels per unit of time. Like any wave, the speed of a sound wave refers to how fast the disturbance is passed from particle to particle. As one particle becomes disturbed, it exerts a force on the next adjacent particle, thus disturbing that particle from rest and transporting the energy through the medium. According to his own recollection of events leading to his thoughts about the problem of electromagnetics in moving bodies, that was not the case.A sound wave is a pressure disturbance that travels through a medium by means of particle-to-particle interaction. Whether or not Einstein had the null result of the Michelson-Morley experiment in mind is not clear. waves are not oscillations of some elastic substance which would define another preferred frame of reference by its rest frame. This of course implicitly implied that there is no "aether", i.e., the em. Seen from the inertial rest frame of the light source this means that any observer moving with constant velocity in this frame observes the same phase velocity of the emitted light waves or, seen from the frame of any observer moving in the light-source frame the velocity of the light source. quantities might look like, the space-time transformations must be such that the phase velocity of em. The ingenious act was to precisely pick up the one most simple piece contained in the Maxwell equations, which is relevant to get the spacetime transformation and makes the Maxwell equations fail to be Galilei invariant: The appearance of a fundamental constant of the dimension velocity in Maxwell's equations, i.e., the phase velocity of electromagnetic waves, #c#, and the form invariance of Maxwell's equations implies that no matter how the transformation rules of all the em. field components, charge and current density, kinematics of "electrons"). So he had to find a spacetime description and transformation laws from one frame to the other for all the physical quantities involved in electrodynamics (em. Einstein's argument in the famous 1905 paper on moving bodies was in terms of a symmetry principle, i.e., in modern terms he demanded to find a spacetime description such that (a) the special principle of relativity is fulfilled (tacitly assuming also that in any inertial frame an observer finds the geometry of space to by Euclidean) and (b) the Maxwell equations are form invariant. I think Einstein wanted to give a physical operational definition of the reference frames involved, and indeed there are two frames of reference involved here: the rest frame of the light source and the observer's rest frame. ![]() ![]() I think he's distinguishing his theory from both ether theory, where the speed of light is #c# relative to the ether, and ballistic theory, where the speed of light is #c# relative to the emitter.
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