Pressure Lesson Outline

Pressure

Suggested materials:

• PSI stick (any ~15lb representation of atmospheric pressure will do)
• Syringes (large enough to fit a marshmallow!)
• Marshmallows
• Mentos
• Diet Coke
• Water pressure cylinder (https://www.youtube.com/watch?v=Bkwf2gjHPd4)
• This is easy to make yourself, if you don't have access to an official one. Simply take a plastic bottle and poke three holes down one side.

Important points:

• Begin by asking for a definition of pressure.
• Pressure can be easy to conceptualize but difficult to define. We thought that, in order to show true understanding of a concept, one should be able to explain it.
• We defined pressure as the force exerted by on or against an object by something in contact with it.
• Pressure is not always visible; there is pressure on us all the time by molecules in the atmosphere.
• This is a good opportunity to pass around the atmospheric pressure representation.
• Analogy: a child who has ingested copious amounts of caffeine running about in a room. Will he hit the walls more in a small room as opposed to a larger room? This child represents a gas molecule creating pressure.
• Connect pressure to volume - this is a good opportunity to do the demonstration with marshmallows in syringes. Allow the students to see what happens when volume within the syringe is increased and decreased.
• Note - begin by asking the students to hypothesize about the connection between volume and pressure.
• Now is a good time to talk about pressure at different altitudes. Begin by asking the students where they think pressure is greatest - at sea level, above sea level, or below sea level. 
• Explain that pressure decreases as altitude increases and vice versa, with reference to gravity and changes in atmosphere density (gravity pulls molecules down, therefore the atmosphere is denser at lower altitudes).
• Introduce the water pressure cylinder. Begin by asking the students to hypothesize about the results; which hole do they think will allow water to escape the fastest?
• Explain the results to the students: explain that the water at the bottom of the container is under greater pressure due to the weight of the water on top of it and, thus, is forced out of the hole faster.
• Optional: introduce a math component. We used Boyle's law (P1V1 = P2V2). This demonstrates an important algebraic concept (plugging in and isolation of variables) and puts the math in the context of pressure and volume.