This applet simulate an impulse moved inside a fixed region.
The impulse will be reflected at the boundary.
The right side is a fixed end boundary while the left side is a free end boundary.

You can use slider to change the width of the impulse.
The function of the impulse is $y(t)=h*e^{\tfrac{(x-v*t)^2}{2\sigma^2}}$, where $\sigma$ control width of the gaussian shape pulse.