1. Activate prior knowledge by asking students to define pressure and give illustrative examples.
Accept several definitions of pressure. Then write the pressure equation (pressure = force/area) on the board and define pressure as the amount of force applied over a specific area. Ask for several volunteers to share examples that illustrate pressure. For example, a student might say “snowshoes versus regular shoes” or “a sharp knife versus a dull knife.” After you write each example on the board, ask students to explain how the example illustrates pressure. If students do not offer examples involving fluids, encourage them to do so. For example, they might mention the pressure a person feels in their ears when they dive deep under water or when they fly in a plane. Refer students to the pressure equation on the board. Ask: What would happen to the pressure if force increased? (The pressure would increase.) What would happen to pressure if the area increased? (The pressure would decrease.) How would you describe the relationship between pressure and force? (Pressure and force are directly proportional; pressure increases proportionally with an increase in force.) How would you describe the relationship between pressure and area? (Pressure and area are inversely proportional; pressure decreases proportionally with an increase in area.) For example, the force a person exerts on snow when walking on it is the person’s weight. Snowshoes spread this force out over a greater area than regular shoes; therefore, less pressure is applied to the snow. Explain that in this activity, students will be examining pressure in a fluid, specifically water, more closely. Leave the equation on the board for students’ reference throughout the activity.

2. Introduce the DEEPSEA CHALLENGE expedition.
Provide students with the following focus questions prior to showing them the video, "Environment News: James Cameron Breaks Solo Dive Record":

• Where did the submersible dive?
• What effect did pressure have on the submersible under water?
• Why was the dive important?

Show students the video and ask them to take notes on these questions as they watch. At the end of the video, discuss the focus questions. Ask students if they were surprised to hear how much the submersible shrank under the pressure of the water. Ask: Why was the pressure on the submersible so great in the Mariana Trench? Describe this change in pressure using the pressure equation (pressure = force/area). Which variable in this equation changed the most as James Cameron went deeper in the ocean? (The variable of force—the weight of the water—changed the most.)

3. Have students conduct a demonstration to examine how pressure changes in different depths of water.
Divide students into small groups. Distribute the Demonstration 1: Pressure Streams worksheet and the materials listed on that worksheet to each group. Review the procedure described on the worksheet with students and answer any questions. Have students make a prediction, conduct the demonstration, and record their data and observations as described on the worksheet.

4. Review with students how and why the two streams were different in the Demonstration 1: Pressure Streams activity.
When students have completed the demonstration, ask them to share their results with the class. Ask: What did you observe? Did it match your predictions? How can you explain what you saw in terms of pressure? (The water exited the bottom hole with more force because there was greater pressure at that depth due to the greater mass of the water above that point. Since the pressure was greater at that depth and the area over which it was applied (the size of the hole) was the same at both depths, the force with which the water exited the bottom hole was greater than the force with which it exited the top hole.) Make sure that students can properly explain what they observed in terms of force and pressure. If necessary, illustrate this to the class using specific variables from the pressure and force equations: Go back to the pressure equation you wrote on the board (pressure = force/area). Go through each variable in the equation as it relates to the bottom hole in the demonstration; then repeat for the top hole. Pressure at the bottom hole was greater than pressure at the top hole because force was greater at the bottom hole and area stayed the same.

5. Have students conduct Demonstration 2: Measuring Pressure.
Distribute to each group the Demonstration 2: Measuring Pressure worksheet and the supplies listed on the worksheet. Have each group assemble a manometer as described in the Demonstration 2: Measuring Pressure worksheet. Be sure students understand that as the pressure increases, the level of the water will rise on the right side of the ruler. Have students discuss what they think will happen to the pressure as they lower the funnel in the water, and ask them to record their predictions on the worksheet. Have them test the pressure at several different levels and record the results on the worksheet. Also have students test with the funnel facing in different directions at the same depth and note any differences.

6. Discuss how the measurements changed with depth in Demonstration 2: Measuring Pressure.
Ask groups to share what they observed in this demonstration. Ask students to explain why the pressure increased as depth increased and to explain why the pressure reading was the same no matter which direction the funnel faced. Identify and address any misconceptions about pressure in fluids at this time. Common misconceptions include the idea that pressure only occurs during movement and that pressure is only applied downward. To address these misconceptions, ask: What would happen if a hole opened on the side of Cameron’s submersible while it was descending to the bottom of the ocean? What if the hole opened while the submersible was sitting still at the bottom of the ocean? Guide students to answer that both situations would lead to an inrush of water.

7. Show students the "Cameron’s Long Way Down: Mariana Trench" video, which includes a one-minute video recap of James Cameron’s dive to the Mariana Trench. 
Prior to viewing the video, ask students to note the pressure changes during Cameron’s descent. Explain that the pressure is different at different locations. Brainstorm some factors that would influence how much pressure is felt at different locations both above and below sea level. Divide students into pairs, and distribute the Calculating Pressure worksheet. Give students the rule-of-thumb calculation for pressure underwater: pressure increases by 0.445 psi per foot of water. The total pressure on an object underwater also includes air pressure, so 14.7 psi—the standard air pressure at sea level— must be added to each of the students' underwater calculations. Have students calculate and record the pressure for the locations on the table. Review the table and discuss the data.

8. Have students create models to show how and why pressure increases at greater depths in the ocean.
Explain that students will work with their partners to develop models to show how and why pressure increases at greater depths in the ocean. Tell students that the models could be illustrations, physical models, or demonstrations, but that they also must be able to use the models to explain how and why pressure increases as depth increases. Distribute the Exploring Pressure Model Rubric and review it with students to be sure they understand what is expected of them in this activity. Make available to students an assortment of materials such as packing peanuts, balloons, marshmallows, Styrofoam balls, and other items. Once students have created their models, have them present the models to the class.