Data and Discussion

Hypothesis vs. Results:

The results of our experiment confirm our hypothesis that height, oscillation, and surface area affect the formation of a bubble on the surface of the larger pool of water that the drop penetrates. Our hypothesis where formed after reviewing our preliminary data.

The distance that the drop is released from has a great amount to do with the chances of a bubble forming. In our preliminary high speed video shoot, we found that when we increased the distance by about 0.5 meters that the chance of a bubble forming was greater. We then hypothesized that this happened because of a few things, the drop had more time to oscillate and become spherical, and since velocity is directly related to distance that the drop travels. Thus, the velocity was greater when the drop was released from a height of 2.0 meters rather than 1.5 meters.

Oscillation of the drop before it hits the larger body of water is extremely important in the formation of a bubble. Oscillation is directly related to height, therefore to study the oscillation we increased the height and analyzed the shape of the drop right before it penetrated the water through our high speed video clips. When a drop has farther to fall it has more time to oscillate and become spherical. We had hypothesized that when a drop was more spherical it was more likely to form a bubble. Our results support this hypothesis. In all of the clips with non forming bubbles, the splash was either oblong, or almost flat when it hit the water. The better bubbles that where formed came from uniform, spherical drops. Therefore, you have a greater chance of seeing bubble formation if the distance of the drop and larger body of water is increased.

How a bubble is formed (or not):

First off, every splash begins exactly the same way. After the drop penetrates the surface, a crown begins to form around the point if penetration. As the drop displaces more of the water, the displaced water is fed into the walls of the crown. What happens at this point is the defining factor in determining whether or not a bubble will form. As water is being fed into the walls of the splash, the walls grow higher and can eventually curl inwards and meet directly above the point of penetration. This meeting of the walls is what we refer to as the dome of the splash. Without a dome, a bubble can never form.

The second stage of bubble formation, the main point is if the dome is willing to close or not. If it does close then a bubble can be formed, yet if does not then there is a problem and a column forms instead of a bubble. Examples of each are seen here:

We then studied what happened to the forming bubble. We did not do much else with the non bubble forming photographs. After the bubble forms it caves in on itself. A jet stream flows into the middle of it and another jet stream comes up from under the surface. This process determines if the bubble will stay on the surface or not. If the jet streams break the bubble, then it has formed, yet will not form. Here are two frames of jet streams in the middle of the formed bubble:

If the jet stream leaves the bubble unharmed then it is possible for a bubble to be standing on the surface of the water longer than a half a second or two. The outcome of the jet stream is critical to a standing bubble. Here is an example of one such bubble:

To fully understand the steps that a bubble must go through to form, one must see this process through a video clip. The following clips will allow you to see just how the drop goes through each of the stages explained above, eventually becoming a bubble.