Circular Motion - Physics 101 / AP Physics 1 Review with Dianna Cowern

I am a high school student and I am very confused in an argument ,people says that when we generate any disturbance{wave} in a string, suppose that I have generated a simple harmonic wave on string in which all particles are performing Simple harmonic motion, suppose the wave is travelling and it just disturbs the particle which was initially at rest, people says that it disturbs the particle by exerting some kind of force on it , but how can there be any net force on the mean position?

 why no one talks about how these disturbances are propagated from one particle to another dynamically{in terms of forces}. I think if we talk by what mechanism, these disturbances are generated it would become much more complicated for us{high school students}, so we all talk of waves only mathematically.