Background

fluid Pressure

The pressure in a fluid is caused by the weight of the fluid above it. Pressure is defined as Force/Area, so in metric units the pressure would be in N/m2 . We call this unit a Pascal (1 Pa = 1 N/m2 ). The atmosphere, the air above us, exerts a pressure on us (at sea level) of 101324 Pa or 101.324 kPa. If we go higher in the atmosphere not as much air is above us so the pressure drops.

The pressure under water is due to the weight of the water above you plus the atmosphere above that. If you are a depth h under the water, the total pressure on you should be:

Total pressure = 101.3 kPa + (density*gravity*h).

Gravity is the usual 9.8 m/s2 and the depth h is in meters. The density will be some number (you will solve for it later on) with units kg/m3 .

What to do

Open up the Excel sheet for this lab (Lab 9).

Simulation Open up your browser and click here http://www.thephysicsaviary.com/Physics/Programs/Labs/DeepSeaDiverLab/ 1. Deep Sea Diver Pressure sim . You are piloting a sub around in the ocean. The pressure sensor on your sub is found at the nose of the sub - it's the black line sticking out a little from the front. When measuring depth of the sub, measure the depth of this pressure sensor. . Use the arrows in the bottom left corner to navigate the sub around the screen making sure you do not run into any obstacles. . When your sub is at rest, you can hit the data button to get a view from inside the sub at the instrument panels. This is where you will find your pressure reading. . When you are ready, click Begin. a. What does the Pressure meter read at the beginning? What depth are you at? b. Pilot the sub upward as far as it will go (not much farther). What happens to the pressure? Does it increase or decrease? c. Next, you will pilot the sub around and take pressure readings. If you run into the rock (bottom or side) you will be reset to the beginning position. You should get readings at 12 different positions between around 0.5 meters and 45 meters depth. Record these values in the Excel table. d. Make a graph of Depth vs. Pressure. Label the axes, give it a title, and plot a best-fit line. Remember to display the equation of the line. Is the graph linear? What is the slope of the line? e. Based on your data, what would the pressure be at a depth of 60 meters? f. Based on your data, what would the pressure be at a depth of 95 meters? g. Based on your data or graph, what is the density of the water? Use the equation at the beginning to solve for the density