What is pressure and how does it affect divers?
The depth at which Aquarius scientists work means they are under quite a bit of pressure, pressure exerted by water. This series of explorations will take you through something that all of us deal with but is especially important to underwater divers — pressure.
Crushed by Air?
Here Is What You Will Need:
- Yardstick (or a meter stick)
- String (about 4 feet)
- 3 Balloons (must be the same size)
- Scissors
- A Heavy Book or Modeling Clay
- 2 pencils (one to write with)
- paper
Safety Rules: Scissors are sharp! Use safety scissors or have adult supervision when using scissors.
Directions:
- Write down all of your observations and the answers to any questions asked.
- Use the heavy book or the clay to hold the pencil so the end hangs over the edge of the table.
- Carefully cut the string into four equal pieces about 12 inches each.
- You will be using your yardstick as a balance, so tie a string to the center and the other end to the end of the pencil that is hanging over the edge of the table. Move the string on the stick until the stick hangs balanced.
- Take two balloons, that are not inflated and tie strings to them. Hang one on each end of the balanced yardstick an equal distance from the support string. Move them, if needed, until the stick is once again balanced. Why doesn’t the stick tilt one way or another?
- Inflate the third balloon and tie the string to one end and make a loop in the other.
- Remove one of the uninflated balloons and replace it with the balloon that is inflated. What happens to the yardstick?
You Be The Scientist:
- Get another balloon, the same size, and blow it up so that it’s larger (or smaller) than the inflated one already hanging on the yardstick. What do you think will happen if you use this one to replace the other uninflated balloon hanging on the yardstick? (Hypothesis)
- Replace the uninflated balloon with the one you just blew up. (Experiment)
- Write down what happened. (Observations)
- Why do you think that happened? (Conclusion)
Connecting To Aquarius:
We saw from our previous experiments that air has weight. The balance would always tip toward the inflated balloon. The weight of Earth’s atmosphere is always pushing down on us with its weight. We define this weight pushing in on us as atmospheric pressure. Pressure is defined as force acting on a unit area. Scientists have calculated that the Earth’s atmosphere exerts a force on our bodies equal to 14.7 pounds per square inch. Another way to think of it is that a one inch column of air as tall as the atmosphere would weigh 14.7 pounds. This measurement, of atmospheric pressure at sea level, is also known as 1 Atmosphere of Pressure, or 1 ATM.
Now, we know water definitely has weight, and weighs much more than air and thus exerts a greater pressure. A one inch column of water 33 feet tall weighs 14.7 pounds. This pressure, resulting from the weight of water is called hydrostatic pressure. So at a depth of 33 feet, a diver experiences atmospheric and hydrostatic pressure equal to twice the amount of atmospheric pressure. We call this 2 ATA, one from the atmosphere and one from the water. This is called absolute pressure. That means our diver is under a pressure of 29.4 pounds per square inch (psi). At 66 feet down a diver is at 3 ATA and experiences a pressure of 44.1 pounds per square inch, and so on.
Aquarius scientists use gauges that measure their depth. When working underwater, it’s always important for the diver to know their depth because this affects their air usage. These gauges work based on the water pressure. Gauge pressure is different from absolute pressure because it ignores the 14.7 pounds per square inch of the atmosphere. At sea level the gauge would read 0 (zero) feet, which is also considered 0 (zero) pressure.
Find Out More:
- Learn about the effects of pressure on divers.
- Learn how scientists in Aquarius stay underwater for days.
- Learn about tanks and regulators.
Lesson design by Lucas Gillispie.