For the first few weeks of our scuba unit we have been learning about gasses and how they react to changes in pressure and temperature. Our first topic of study was pressure; we explored the pressure that the atmosphere exerts on our bodies and compared that to the pressure of saltwater and freshwater. What we learned was pretty amazing; because water is so much heavier than air, it takes only 33ft of saltwater to equal the same pressure (14.7 psi) that the atmosphere places on us. In order to demonstrate the effects of pressure, we conducted the “Let it Flow” experiment and then used manipulatives to help us calculate the pressure of both salt and freshwater. Here are a couple of pictures of students calculating these values.
After we had a basic understanding of how air and water pressure compare, we took a careful look at how pressure affects the volume of a gas. “Squidy”, a Cartesian diver, was a great inquiry based experiment that allowed us to figure out the relationship between pressure and volume. After a lot of trial and error, we learned that there is an inverse relationship between pressure and volume that can be quantified using Boyle’s Law. (P1)(V1)=(P2)(V2) It was a lot of fun to use Boyle’s law to calculate how long a given amount of air would last for a scuba diver at various depths. Below, you can see some pictures of our work with “Squidy”.
The final gas laws we explored were Dalton’s Law and Charles’ Law. Dalton’s Law is concerned with partial pressure of gasses. Student’s learned that as divers go deeper and pressure increases, a gas begins to “act” like a higher percentage of that same gas would at the surface. We then discovered that this principle can be used to explain things like oxygen toxicity, decompression sickness, and nitrogen narcosis.
With Charles’ Law we explored the concepts of temperature, volume, and pressure; our important lesson from this law was not to leave a full scuba tank in the back of a hot car in the summer. When the temperature increases and the rigid tank prevents the volume from increasing, the inevitable consequence is a change in pressure which can result in a burst disk on the tank. Armed with a good understanding of diving physics, how gases react to pressure, and what can happen to our body if we fail to take proper precautions, we are now ready to begin our study of dive tables.
