Air Pressure Curriculum

Section 1—Lesson 1: Air Pressure is Non-obvious but Causes Effects

Lesson Plan

Materials

Prep Step

Analyze Thinking

Step 1: Consider the Historical Problem of Pumping Water out of Mines

Pose the following problem, which was encountered by miners in the 1500's:

Miners in the late 1500's faced a problem. Water would flow into the mines when they were excavated to a certain depth, and the miners could not find effective ways to remove the water. Therefore, they would end up abandoning mines that still held silver, iron, salt, alum, and other valuable minerals. A former doctor who was interested in science named Bauer identified the problem as having to do with the depth of the mine shafts. In his writings, he described the most common three methods that were used to remove water, either in combination or separately. The first used cloth balls on a circular chain that soaked up the water at the bottom of the shaft, and were squeezed out at the top of the shaft, and then went back down to collect more water. A second used a giant screw that, as it turned, forced the water upwards. The third used a rotating waterwheel shaft with a crank attached that operated a piston which was partially in the water. It would "suck" water into the cylinder, and then a valve would close at the bottom and open at the top, and as the piston came down the water was forced upwards. The third method worked best of the three but curiously, it could not "lift" water more than 32 feet. Abandoning productive mines was expensive, but it wasn't until 1630 that the problem was solved.3

Review how the miners pumped water out of the mines. Make a drawing on the board to help students visualize the process.

Ask students to work in groups of 3 or 4 and to generate a list of possible problems that might have interfered with pumping water from the mines. Encourage students to draw diagrams or models if it helps them think about the problem.

Ask students to share their ideas with the class. Emphasize that all ideas are valuable. Record their ideas on the board.

RECAST Thinking

Step 2: Experimenting with the Height of a Liquid in a Tube

Distribute to each pair of students one plastic jar, one straw, one transfer pipette, and one piece of gum. Instruct students to:

  • Fill the jar 1/4 of the way with cooking oil (about 1/2 cup), depending upon the diameter of the jar.
  • Chew the stick of gum until it is soft. Then use the gum to plug one end of the straw.
  • Use the pipette to fill the straw 1/2 way with cooking oil, then quickly invert the straw into the jar of cooking oil.
  • Tape the straw to the inside of the jar. Make sure the straw is at least 1 cm above the bottom of the jar.
  • Use a permanent marker to mark the level of the oil on the straw and on the jar.
  • Label the jars and set them in an area that does not undergo large fluctuations in temperature.
Photo of straw in jar Sketch of straw in jar

Step 3: Discussing the Height of a Liquid in a Tube

Ask your students to notice the height of the liquid in the tube. Ask them to consider the behavior of the liquid in the tube.

  • Why does the liquid stay in the tube?
  • Why doesn't gravity make the liquid fall out of the tube?
  • Why does the liquid stay at the level that it does? Can you do anything to get the level to change?

Note to Teacher: Have your students set the jars aside and observe them on a regular basis to see what is happening in the straw and jar. If the students in your class think that the liquid stays in the tube because of a vacuum and/or do not see outside air pressure as the cause of the liquid staying in the tube, then you should observe the height of the liquid in the straw (as in Steps 2 through 4 of the next lesson) and then come back to the rest of this lesson.

Explore Causality

Step 4: Thinking About Hidden or Non-obvious Causes

Introduce the idea that some causes are non-obvious. Ask: "What does it mean for something to be non-obvious?" Collect students' ideas. (Things you can't see, things that are hard to notice, things that happen over a long period of time, etc.)

Pass out the sheet, Thinking about Hidden or Non-obvious Causes. Read and discuss the sheet together. While reading, each student should think of one question they have about the sheet and write it down. It can be a question of clarification, something they don't agree with, something that extends what they read, or a situation where they are unsure if pressure plays a role. Elicit students' questions and discuss them as a class.

Check to see if students can offer some examples of non-obvious causes. Ask, "What are some causes that aren't obvious and what do they cause?" If students aren't able to come up with a good list, offer some examples. For instance:

  • A baseball player might have a hidden injury that impacts his or her performance.
  • Someone feels a shock after walking across a rug because he or she has a positive or negative charge caused by an excess of protons or electrons—the phenomenon we commonly call static electricity.
  • Water droplets form on a window when it is warm inside and cold outside.
  • People can float more easily in the ocean than in a pool.

Review, Extend, Apply

Step 5: Connect the Historical Problem and the Liquid in the Tube

Read the passage about pumping water out of mines in the 1500's from Step 1 again. Ask: "How does what you observed with your straws explain what was going on with the pumps in the 1500's?" (Just as air pressure caused the liquid to rise and fall in the straw, air pressure must be the reason why the pumps could only pull water out of the mines to a depth of 32 feet).

As a class, read and discuss the sheet, The Discovery of Air Pressure: A Brief History. Ask the following questions:

  • Do you think the effects of air pressure were obvious to miners in the 1500's? (No)
  • Are the effects of air pressure obvious today? (No)