What physical characteristic of a sound wave should be changed to alter the pitch? The loudness?

When a neutral charge, comes into contact with a positive charge they repel each other nothing happens the neutral charge becomes negative they attract each other

What sort of waves exhibit the doppler effect?

Auniform crate c with mass mc is being transported to the left by a forklift with a constant speed v1. what is the magnitude of the angular momentum of the crate about point a, that is, the point of contact between the front tire of the forklift and the ground