You stir coffee in hot water and tap the side of cup, the pitch of sound produced by the tapping changes greatly as the coffee is added and as you stir. Why does this happen?
A. Air trapped in the instant coffee power is released as you stir it.
B. Coffee lowers the temperature of the hot water, lowering the speed of sound.
C. Coffee forms a temporary thin film on the top of the water which reflects some of the sound and changes its frequency by superposition effects.
Physics! FUN~FUN~FUN~~~
2007-06-25 8:03 pm
回答 (1)
2007-06-25 8:09 pm
✔ 最佳答案
Answer My Coffee Sounds Funny - Answer = A The air trapped in the instant coffee is initially mixed with the water forming an air-water mixture. Since the speed of sound is lower in this mixture than in pure water (or coffee), the resonance frequency in the coffee cup produced by the tapping is lowered. As the air bubbles escape with additional stirring the resonance frequency rises (since the velocity of the sound increases).
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