Posted by: Kirsten | Saturday, 15 September 2007

The pressure is on… Are we there yet?

Are we there yet?

Sometimes, getting from point A to B seems to take an eternity. All those miles to drive and the Gameboy and Ipod batteries are completely dead.  Now what?

If you look around in the clutter of your vehicle, you might find the makings of a cool science experiment to pass the time, AND the miles.

Sometimes you plan ahead for these sorts of things, and sometimes you discover them by accident.  My son and I were driving across the expanse of north central Wyoming a couple of weeks ago when I noticed much of the air had been seemingly squeezed out of one of our half-full water bottles. Then it dawned on me — a teaching moment!

Unfortunately, because we had just reached our destination and I had just opened the bottle for a drink, it was an inconvenient time to show my son the impromptu lesson on atmospheric pressure and the concept of barometers, but I filed the idea in the back of my mind for our return trip.

Materials needed: Plastic water bottle with lid, half full or half empty, your choice.

Step 1: Drive to top of mountain pass. We’ll call this Point A.

Step 2: While at or near highest elevation on your drive, open bottle, then reseal.  Note to your kids that the pressure inside and outside the bottle is now the same. Have the kids make predictions as to what might happen as you drop in elevation.

Step 3: Watch the bottle as your vehicle descends the mountain road. Note to driver — leave the observing to the rest of the family.

Step 4: Drive downhill until you’ve reached a low spot, your ears have popped, or both (Point B).  A thousand-foot drop in elevation should be sufficient, but in some places out west you can get 4,000 to 5,000 foot drops over a span of 20 miles.

Water bottle barometer
This simple experiment demonstrates that there is lower air pressure at higher elevations (less of the atmosphere above pushing down on us) and higher pressure at lower elevations (we’ve gone lower, so there’s more of the atmosphere above us).

You can reverse the experiment and do it while climbing the mountain as well, but the results are less dramatic. When opening the water bottle, even after a several-thousand-foot climb, you might not see that the plastic bottle is bulging a bit, but you’ll definitely note the audible “hiss” of air as the bottle is opened. A better way to demonstrate the higher pressure inside your container is using yogurt containers if you have them with you.  Our yogurt lids showed a definite bulging effect as we climbed the hills and when opened, burped out lovely slops of yogurt in our direction if we weren’t careful.  Very cool!

If you have any other ideas for science on the road, please consider sharing your ideas here. (No pressure!)

— Jon
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