There were two parts to our experiment, under the water, and above the water. During the wet experiment we put 100ml of air in the tube at the surface. We then brought the tube down by 4-foot increments, measuring the volume of the air bubble. The volume of the air bubble decreased according to Boyle’s Law as we went farther down. We recorded our data on a transparency that was connected to a clipboard.
Between the depths of 0 and 4 feet the difference of the volume was ten ML. But between the depths of 12 and 16 feet the difference was only 5.25 ML. This is because when we were closer to the surface the increase of the pressure had a greater effect on the air bubble. This is important to know for scuba diving, because when people are diving they have to be the most cautious when they are closest to the surface.
We had a very small percentage of error in our wet experiment. The percentage of error was always under 1%. Part of it was because we only had two trials, but we had very close results. If we were to redesign this project, we would make more time for more trials. We also would redesign the system we used to measure the depth. We had a tape measure being held at the surface of the water, with the bottom of the tape measure at the bottom of the pool. If we were to redesign this project we would tie the tape measurer to a piece of Styrofoam to the top of the tape measurer, so it would not sink.
Our experiment used Boyle’s Law, which we used for our hypothesis. However there was a major problem. Boyle’s Law is for salt water, and we did our experiment in fresh water. In salt water an atmosphere is equivalent to 33 feet of salt-water pressure. However since salt water is 1.026 times as dense as fresh water, an atmosphere is equivalent to 34 feet of fresh water pressure. This effected our hypothesis, because we had to do our experimnet in fresh water.
During our dry experiment we simulated a pressure chamber using a 2-liter soda bottle, a bike pump, and a graduated cylinder. We filled the 2-liter bottle 2/3 full with water, and then we dropped the graduated cylinder in the bottle. The test tube was weighted down by a screw, to prevent it from floating. Using a straw we measured 10 ml of air into the test tube. We pumped increments of 10 psi into the bottle and measured the volume of the air bubble. This experiment was an extension of our wet experiment, because we were able to add more pressure to the test tube. Again, the percentage of error was under 1%, so our results were very accurate. If we were to redesign the experiment we would use a better device then the straw, because using the straw was tedious. We could also test much greater pressures if we used something besides the 2-liter soda bottle, because the bottle could only sustain around 80 psi. Our experiment tested Boyle's Law. To show this, here are some examples of Boyle's Law from our results.
This example is comparing our results at the surface to our results of our experiment eight feet under the surface.
P1 x V1= P2 x V2
14.7 x 100= 21.618 x 69
As you can see the results are very close to eachother, so they follow Boyle's Law.
Our Problem Statement was, “How will the volume of the air bubble change under different amounts of pressure?” We concluded that the air bubble decreases in volume as the pressure increases.