Flashes of a thunder are always seen before its sound is heard. Why there is time difference?
Because light travels much faster than sound.
Why does a diver stretches his body before diving and closes his arms and legs after then?
Before diving, he does not want to make somersaults (Rotations of the body) so he stretches his body to make larger the moment of inertia. But after jumping up he wants to perform somersaults so he closes his arms and legs to decrease the moment of inertia, Consequently, he gets rotations (angular velocity) to conserve the Angular momentum. Which is the product of the moment of inertia and angular velocity.
Do all the moving charges produce electromagnetic waves?
No. Only the charges moving with varying velocity produce electromagnetic waves. And the charges moving with uniform velocities will not produce electromagnetic waves.