Mass acceleration or deceleration causes collisions with nearby particles, which collide with farther away masses, and so on, and the disturbance {wave, physics} continues outward at speed that depends on medium particle-connection strength.
mechanical waves
Water-table waves illustrate transverse mechanical waves. Long springs, such as slinkys, illustrate longitudinal mechanical waves. Tuning forks, guitar strings, bongs, and glasses with water at different levels illustrate mechanical longitudinal sound waves. Mechanical waves are in media, which determine wave velocity by electric forces between molecules.
longitudinal wave
Disturbances, such as collisions, can be along line between two masses. Imparting force requires acceleration. Molecules move toward nearby masses, hit them, and bounce backward. Hit molecules accelerate, move toward next masses, hit them, and bounce backward, and so on. Bounce-backs return masses to where they were before, and only heat remains, so no net mass moves. Only disturbance and energy move outward. Wave velocity depends on material elasticity.
transverse wave
Disturbances, such as plucking strings, can be perpendicular to line between two masses. Molecules accelerate transverse to line between two masses. Nearby molecules feel transverse pull, because molecules attract. Attractions eventually stop transverse motion and reverse it. Cycle repeats until only heat remains. No net mass moves along, or transverse to, line between masses. Only disturbance and energy move down line, in both directions. Wave velocity depends on material elasticity.
movement
Waves have to travel, because they must pass from mass to mass. Waves involve acceleration and decelerations.
properties
Mechanical waves displace mass from equilibrium position. Waves have maximum displacement amplitude before they return to equilibrium point. Wave trains have frequency of disturbances passing space point per second. Wave trains have period between disturbances. Waves have wavelength between first and second equilibrium points and have wavelength inverse or wave number. Waves have phase angle of displacement to amplitude. Waves have speed of disturbance travel.
electromagnetic waves
Charge acceleration or deceleration causes force-field change {half-wave, charge acceleration}, which travels outward at light speed. Charge-acceleration moments make photons, because photons have spin. After first acceleration or deceleration, reverse deceleration or acceleration can add half-wave disturbance in opposite direction, to make one complete wave. Repeated acceleration and deceleration can make wave train. Electromagnetic waves do not have position displacement, only field displacement.
Electromagnetic induction requires changing electric and magnetic fields. Electromagnetic-induction rate determines light speed and depends on electric-force strength. Changing electric and magnetic fields move induction point away from accelerating charge. Therefore, light cannot be at rest. Behind moving point, fields cancel. Photons are only at one point, so light has no motion relative to other reference points, and in vacuum, light has same speed for stationary and moving observers.
Electromagnetic induction does not need or have medium. Because light does not move in medium, light speed is not relative to medium. Light speed is absolute maximum speed.
Photons have no mass, so light has no inertia and moves as fast as anything can move. Light speed is maximum physical speed.
Light electric and magnetic fields from several sources add, because electromagnetic inductions add. In media, atoms and molecules absorb and emit light, and this slows light speed but does not change frequency or intensity.
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Date Modified: 2022.0224