Air is, of course, everywhere (except in a vacuum and underwater—more or less). It is constantly pressing down on everyone and everything, but, fortunately, weighs almost nothing, and so this pressure doesn’t really affect us. But, there are many instances where pressurized air does have an impact. Car and bike tires rely on pressurized air to keep us rolling along; blasts of pressurized air are used to clear away debris in certain manufacturing processes.
However, short of bringing an air compressor into the classroom, how can you demonstrate the properties and effects of air pressure to your students? Why, with this quick and easy Demo Science experiment, of course!
Huffin’ & Puffin’ for Science
For this experiment, you’ll need to equip each student with an empty, small-mouthed plastic bottle (like a water bottle) and a piece of scrap paper. You can have the kids bring in their own bottles, or supply them yourself. The scrap paper should be a gimme in a school setting.
Instruct each of your smelly students to secure his/her empty bottle to the top of his/her desk with a few strips of masking tape. (You need tape for this demonstration, too, BTW.) The bottle should be on its side, roughly in the middle of the desk. Have each kid rip off a little piece of the paper and roll it into a ball about the size of a pea; these paper wads should then be placed just inside the mouths of the bottles. (One per bottle, if that’s not obvious.)
Have your charges lean down and put their chinny chin chins on their desks, facing the opening of and about six inches away from their respective bottles. Then, have them blow as hard and fast as they can into the bottle. If all goes as it should, the wad of paper will shoot out of the opening, right back at the blower. (If this does not happen, have students adjust the placement of the paper ball and the angle from which they’re blowing. They’ll get it before too long.)
So, why does the paper come flying out like that? Shouldn’t the air blow it into the bottle instead of out of it? The rapidly moving air flows over the paper ball and hits the sides and bottom of the bottle, which increases the air pressure inside the bottle. The increase in pressure pushes most of the air out in an attempt to equalize this pressure. This, in turn, pushes the wad of paper out, too. BOOM! Air pressure.