Unit 2 Reflections: Pressure, Straws, and Blow Up A Kid

I'm not sure if today was the best use of our time.  I don't feel like my students have any better "mental image" of pressure after the two activities.

Part of this may be my own misconceptions, but I'm not exactly sure how playing with a drinking straw is a good introduction to the idea of pressure.  The synopsis:  lab groups were given straws and a cup of water to play with and told to develop and white board a "trick" they can do.  Our workshop leader suggested doing this to engage them.  95% of the groups did the putting your finger over the top of the straw trick.  We didn't have any good discussion on suction, except that we are pulling air particles out, which causes other particles to take its place.  We kind of wasted 15 minutes of class time playing with no "ah ha"  moments.

Then we did the "blow up a kid" demo.  For this, you need a trash bag, sealed with duct tape, with 4 straws inserted into the corners:

I thought this would be a huge hit.  It wasn't.  Surprisingly, no one wanted to be "blown up."  No one wanted to blow on the straws.  The brave souls who did volunteer to blow it up told me the air tasted like other people's bad breath (ick).  And most importantly, I don't think it helped our mental picture of pressure any.  Probably half of my students were having a hard time visualizing that it was the air particles colliding with the bag that provided the force to lift the kid off the table.

The PHET Interactive Simulations helped the students better understand how particles cause pressure.  I strongly recommend using it as a visual at very least.

I put some notes/discussion questions into PowerPoint form for pressure, since there were a lot of particulars with the units that the students are supposed to take away from the discussion.  In the PowerPoint, I defined pressure, introduced the 4 common units (psi, Pa, mmHg, and atm) and talked about hand water pumps and Torricelli.  I also had some slides on barometers and manometers.

The goal was for Worksheet 2- Measuring Pressure to be homework, but they weren't even remotely ready to attempt those problems on their own.  Now I'm kind of wanting to skip them myself-- we're so far behind... I'm not sure if calculating pressure in a manometer is the best use of our time and their brain cells.  We might do it as a class on Monday, although then I won't get a good assessment out of it.

Monday, my goal is to do a modified Boyle's Law lab using clamped pipets and textbooks.  We do not have Vernier equipment at my school.  I have one set that was given to me as part of my modeling workshop, so I plan on breaking that out for a demo for Charles' Law and Avogadro's Law.

I really hope I can recoup some lost time during Unit 3-- I plan on slashing a lot of Unit 3's material.  I really just want students to understand the concept of phase change diagrams, heating and cooling curves, and some basic specific heat problems.  I'm hoping we can do that in 5 days maximum.