●●● ●●●● 2. Experimental principles ●●●●● ●●●● ●●●●● ●●●● 20 △P R △P— The additional pressure which is formed when the water drops down in the wide mouth bottle R>I R=工 R>I The surface tension 2 (N/m) 20, I(1):R-The curvature radius of the bubbleR P P R P 2 1 2 1        1 1 2 p r   = 2 2 2 p r   = 2 2 1 1 p p    =   （1） R P 2  = P R —The additional pressure which is formed when the water drops down in the wide mouth bottle —The curvature radius of the bubble —The surface tension （N/m） 2. Experimental principles