When I was but a wee lad, I always dug going through the bank drive-through with my parents for two reasons. First, the tellers almost always sent a lollipop for me in with my parents’ bank slip (a practice that used to be commonplace but that has most likely been discontinued in our overly-paranoid modern age). Second, I thought the pneumatic tubes that sent the transaction canisters back and forth from the car to the tellers were way cool. I always wanted to be the one to push the button to send it back—my success rate in that respect generally depended on who was driving.
As online banking is pretty much the standard now, it’s entirely possible that your students have never experienced the joy of pressing that button and hearing the accompanying swoosh as the air kicked in and shot the canister down (or up) the tubes. With that in mind, here’s a simple science demonstration that will help you show the smelly little buggers just how cool pneumatics can be.
Blow Their Minds with Air Power
Materials-wise, you’ll need a bunch of drinking straws, a bunch of popsicle sticks, a bunch of jumbo popsicle sticks (you might know them as something else, but extra wide popsicle sticks is what I’m referring to here), some zip ties, some plastic syringes, thin plastic tubing that fits over the ends of said syringes, and several rolls of masking tape. And, if you’re feeling sassy, a bag of mini marshmallows.
You can divide this next section up amongst your students to create an assembly-line type solution to get it done quicker. You’ll need half your drinking straws cut into quarters, and half of them cut into eighths; your plastic tubing needs to be cut into roughly six inch lengths.
Break the kids out into teams of two to four (depending on the size of your class) and distribute six quarter-length straws, two eighth-length straws, one piece of tubing, nine normal and two jumbo popsicle sticks, a handful of pipe cleaners, two plastic syringes, and a roll of tape to each team.
First, the kids must construct the frame of their pneumatic device. Using the longer straw pieces as corner “hinges”, have them construct two triangles per team using the standard popsicle sticks. Then, connect and brace these triangles together with crossbars of standard popsicle sticks and tape. You can spell or diagram out how you want these frames to work, or leave your students to their own devices and see how it shakes out.
Then, on whatever side of their frames the kids determine is the strongest, have them add a jumbo popsicle stick, securing it vertically with tape. This is the first part of the “hinge” that the device will move with its awesome pneumatic power. Tape one of the 1/8 pieces of straw to the top, perpendicular to the stick. Tape another 1/8 straw to the end of the other jumbo popsicle stick to form the other half of the hinge. Then, secure the ends together with a pipe cleaner—make sure they’re pulled together tight, but not so tight that it will pull the tape off. Twist the pipe cleaner tightly and trim the excess.
Now, the pneumatic system. Connect the top of the stopper of one of the syringes to the top half of the popsicle stick hinge with another pipe cleaner. Connect one end of the tubing to the nozzle of the syringe, then tape the nozzle-tube connection to the base of the first jumbo popsicle stick (the one taped to the frame). From there, simply connect the other end of the tubing to the other syringe’s nozzle. Pop the stopper out of the second syringe and slide it gently back in a little way, filling it with air.
If it all worked as planned, depressing the stopper on the second syringe should press the first syringe’s stopper out, lifting the jumbo stick arm above it. Have your students tweak their systems to get maximum movement and speed. When they’ve got it all squared up (and, again, if you’re feeling sassy), give ‘em all a little pile of marshmallows and see whose pneumatic gizmo can launch them the farthest.
Technically A Dense Phase System
Pneumatic systems are either dilute phase (low pressure, high speed) or dense phase (high pressure, low speed). What your students have constructed here would technically be a dense phase system, as the small scale and the thin tubing provide high pressure, while any movement of the system, no matter how “fast”, will actually be pretty slow in the grand scale of things, as it is manually powered. It’s not necessarily all that important that students know this dilute phase vs. dense phase bushwah, but there’s no such thing as “learning too much.”