RE: [obm-l] Medida Positiva e Interior Vazio

["Qwert Smith" <lord_qwert@xxxxxxxxxxx>]

>From: "claudio\.buffara" <claudio.buffara@terra.com.br>
>
>No mais, alguém já descobriu por que um chicote estala quando é usado?
>
>[]s,
>Claudio.

Today's Question:

    Why does a whip make a "crack" noise?



The Answer:

    The "crack" occurs when the wave of motion traveling down a whip 
surpasses the speed of sound. The wave can move so quickly because a whip 
tapers from the handle to the tip. When a whip is snapped, the momentum from 
the motion at the handle is conserved, and consequently the speed increases 
as the diameter of the whip decreases. Thus the wave gathers speed as it 
continues down the length of the whip, and when its velocity exceeds the 
speed of sound it produces a small sonic boom — the distinctive "crack".

    —The Editor

source: http://www.infoplease.com/askeds


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