What is the force that is actually pulling the wave down/pushing it up? I can find information talks about the medium used to create the wave can determine its frequency but not what is actually causing that pattern in particular as opposed to a straight line or even a loop d loop.
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There are a couple of good answers already but I get the sense you’re asking at a more general level — what is it that causes something to move like a wave?
The fundamental property of a waveform is that its second derivative is negatively proportional to its value. This is represented by an equation like x” = -kx where k is some constant of proportionality.
What this means tangibly is that when the value goes up, its rate of change goes down and pulls it back; and vice/versa. The “value” we’re talking about depends on the context of course. A few examples:
– Sound waves are waves of air pressure. A local area with higher pressure than its surroundings (more air molecules) will tend to dissipate because the particles repel each other. And again, vice/versa for low pressure.
– Light propagates as a wave because of the homogeneous Maxwell equations, which are two of the fundamental equations of physics. They explicitly imply that the second derivative of the electromagnetic fields are negatively proportional to the strength of the fields themselves.
– A wave that propagates down a rope. Here the “value” is literally the displacement of the rope at any specific point. When it’s large, the rope is pulled tight and tension pulls it back.
All of these follow the same basic principle, and more precisely the same mathematics (they’re described by the wave equation), and that’s why we say they behave like waves.
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