Recent content by bob45

nope i am not speaking about wave equation for a rope, just for the speed of the wave, so the drawing is symetrical and there is no x + dx, just two forces symetrical, so the interval of the rope i want to make smaller and smaller so i want to work with dx or (dl the length of the part of the rope)

if i note x the angle theta, i mean we can use dx instead of Δx, we can look at a infinitesimal angle instead of a little angle.

"OK. But why don't we just use d(Theta) (infinitesimal), the result must also be true, and then the proof is correct for all value of amplitude of the wave (i mean we can just zoom in it and the angles will be small ..) " ... please

hi, when we try to find the speed of a wave on a rope v = (F/u)^1/2, we use the fact that if the angles are small then sin x = x. I understand the approximation but not WHY we use the approximation. We say delta(Theta) is small (and then amplitude is small) then ... . So the proof is only...