縱波既波速點計? - Ans.fyi 參考答案

縱波既波速點計?

2010-03-04 3:00 am

我係中六生, 之前教左v=開方(E/P)
其中E係young modulus, P係密度
之後我諗, 聲音係縱波, 佢係水既傳播速度比係空氣快
水既密度比空氣既高
所以我覺得v係正比於P或者開方P之類咁啦
但條式係反比關係
當然條式就無可能會錯

所以我想問..我究竟搞錯左咩呢?
關吾關young modulus事呢?

謝謝好心人幫忙=]

回答 (1)

天同

2010-03-04 4:32 am

✔ 最佳答案

Yes, you are right. The dependence of the Modulus of Elasticity E on the speed of sound in a medium is more than that on density.

Air has an adiabatic bulk modulus of about 1.4x10^5 N/m2, and a density of 1.2 kg/m3.
Water has a bulk modulus of 2.15 x 10^9 N/m2, and a density of 1000 kg/m3.

The increase in density of water when compared to that of air is about 830 times, but the increase in Elasticity Modulus is about 15,000 times. Hence, the increase in Modulus of Elasticity mostly detemines the speed of sound in the medium.

You could find some examples on the speed of sound in gases, liquids and solids in the following web-page:
http://www.engineeringtoolbox.com/speed-sound-d_82.html

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