都是氣泡惹的禍
當輕敲啤酒杯時，會發覺酒杯發出之聲調隨氣泡漸漸消失而有所改變。為了解氣泡是如何影響頻率，我測試了幾種含氣泡之飲料，以探討當氣泡漸漸消失時，杯子發聲頻率之變化。實驗發現杯子內飲料之氣泡漸漸消失時，裝啤酒與可樂杯子的發聲頻率逐漸增高，然而裝沙士杯子的頻率卻逐漸降低。為解開此相互矛盾的現象，我設計了將液面上之泡沫及液面下之氣泡分開檢驗的實驗。實驗結果發現，液體中氣泡的存在會使杯子發聲頻率變高。而當液體表面受到擾動時，會降低杯子的發聲頻率。若液面上存在泡沫時，杯子的發聲頻率也會變低。這表示裝盛含氣泡飲料杯子音律之變化，須同時考量液內含泡量與液體表面之效應。此結果可以成功的解釋為何啤酒、可樂與沙士於氣泡漸漸消失時，杯子頻率會變高或變低的現象。Tapping the side of a glass of beer as the bubbles escape, one can find that the pitch will change. In order to know how the bubbles would influence the frequency, I survey the pitches of a wine glass with various drinks that would generate bubbles. As bubbles getting away from the glass, my experimental data shows that the frequencies of the tone did get higher when the glass contains beer and coke. However, I surprisingly find a different result when the same glass contains sarsaparilla. Hence I design a series of experiments to understand the possible mechanism. The data suggests that when the drinks contain bubbles in it, the frequencies of the tones will be higher. When the liquid surfaces were disturbed, the frequencies of the tones will become lower. If there were foams above the liquid surfaces, the frequencies of the tones will also be lower. This finding proposes that people needs to consider both the bubble bulk status and surface effects. The consequences of the competitions between these two effects can successfully explain how the tones are changed in the cases of beer or sarsaparilla or coke.