Physics Of The Whip

movie 1
(QuickTime, ~244k)
movie 2
(QuickTime, ~171k)
Windows Users: download Quicktime for Windows
if you do not already have it.

You can imagine a buggy-whip. The main "Gimmick" is the Taper. When swung, the hand moves slowly under twenty miles per hour. A traveling wave moves into the "thick" part, and travels toward the "thin" part. The wave speeds up, because there is less mass to carry the same energy. When the wave reaches the tip, it is a tiny, mass moving faster than sound. The "crack" is a tiny "sonicboom", proving this point. In a similar way, the whipping motion sends a wave of motion from you (heavy) forearm, to your (light) fingertips, which move at tremendous speed. To understand why this is more effective, consider the block of wood. If you hit is slowly, it would bend a little and push back, hard, or it would move away. But hit it fast, and the center part  instantly starts to move, before the rest of the wood even get the message. The wood bends, but has no chance to push back and slow the motion. It breaks. The wood was not able to "bounce back the energy", like a trampoline. The wood nearest the hit was suddenly moving fast, and it bent too far before it could stop.

The wood actually "pulls apart" on the side opposite the hit.

Like most materials, wood can be compressed or pulled sideways, but it is weakest when being torn apart.

Since the wood won't "compress" very much on the inside curve, it ends up getting "stretched" on the outside curve, which is where it starts to crack. The crack then follows the path of stress straight through the wood.

High-Speed Breaks

If the hit is snappy enough, the shock wave goes through the wood and knocks a piece out the other side. The rest breaks as usual.

Here is the same thing on a pool table-the balls touch in a perfect straight line. The incoming ball stops dead. The three center balls never move.

As the fingertip approaches the wood air is trapped under pressure, forming a tiny, cup-shaped depression in the tissue.
So the impact begins before the hand touches the wood, and is cushioned. The effect at the wood is to increase the impact.

The harder the wood, the less it "gives". The shock-wave is "focused" to a small spot on the wood, because the cupped tissue acts like a parabolic reflector. This is the same principle as a "shape charge" explosion used to pierce armor plate.

The previous example show that the hand need not penetrate the wood. Why?

This is called "transfer of momentum" and happens before the wood can move. The hand stops or bounces back, just as the wood begins to move.

Why is this different from a bullet?
The bullet is several times denser than the wood. So the impact force moves the wood before the (equal) breaking force slows the bullet. Also, the bullet moves faster than sound. So the bullet moves into the wood before the shock wave can push the wood out of the way.

Advantages of the WHIP and how it compares to other hits

Copyright © 1998 by Guy L. Savelli. ALL RIGHTS RESERVED.
Except as otherwise provided by law, this writing may not be produced in whole or in part, in any manner.