whip effect in electric conductor
Your electrical whip =  a transmission line where the characteristic impedance grows as the wave propagates. In 2 wire TEM mode lines that means non-parallel wires, the distance between the wires increases along the distance from the signal source.

You have a misunderstanding. It does not make the pulse shorter. The beginning and the end of the pulse need the same time to travel. A whip generates a bang due the incrased transversal velocity which is at the thin end supersonic. That velocity is analoguous with the voltage in the line and it's not the propagation velocity. The motion duration at the banging thin end of a whip is not shorter than the motion duration in the thick end.

You can get the bang also from the electric whip if the voltage exceeds the breakdown voltage of the materials.

In a whip you can increase the transversal velocity easily thousands of percents.  In electronic whip the available change is not that radical.It can be made stronger by having also gradually changing isulation between the wires. In the beginning it should be highly permittive, at the end high magnetic permeability is needed.

The electronic whip effect (=the voltage grows as the signal propagates) can be achieved  by utilizing an electron beam that travels within the electric signal in the line. Amplification in the travelling wave tubes is the practical result.