<p><strong>Fig. 2.18.</strong> Steps in manipulating bottles of liquids to observe gravitational flow between two liquids. (<strong>A</strong>) Add food coloring to one of the bottles and pour liquid into each bottle. (<strong>B</strong>) Invert the top bottle using a card to hold the liquid in the bottle. (<strong>C</strong>) Place the two bottles together. (<strong>D</strong>) Carefully remove the card.</p>

Fig. 2.18. Steps in manipulating bottles of liquids to observe gravitational flow between two liquids. (A) Add food coloring to one of the bottles and pour liquid into each bottle. (B) Invert the top bottle using a card to hold the liquid in the bottle. (C) Place the two bottles together. (D) Carefully remove the card.

Image by Byron Inouye