Hey guys. I have a simple-looking physics problem that I don't really understand, and I remembered this site, where I used to hang out a lot in the beforetime, the long-long ago. (That's a South Park reference). This is the problem: A person blows through a straw between two empty soda cans. Do the cans move closer together or away from each other? Explain why they move the way they do. Partial answer: The cans will move closer together. Given that information, we can conclude that the air pressure in the region between the soda cans must be lower than normal. What I would like to do is explain why the pressure must be lower there without using information about how the cans will move. A lot of sites discuss this, but most of them just say that Bernoulli's principle is responsible. That's not much of an explanation. First of all, I'm not sure how to apply Bernoulli's principle here. (I have never studied fluid dynamics by the way). According to Wikipedia, Bernoulli's principle states that "an increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy". Here's my attempt: Chop up the region in front of the straw into small pieces. If I look at pieces along the straight line defined by the straw, then the average velocity of molecules in a piece will decrease with increasing distance from the straw. Because of this, the principle tells us that the pressure in these pieces will be increasing with increasing distance from the straw. At a large enough distance, the air pressure will be "normal". This means that each of the pieces has a pressure that's lower than normal. Is this a correct way to apply the principle? Even if it is, I don't find the argument convincing. What if I somehow produce a high pressure stream of air? Wouldn't the same argument lead to the same conclusion, that the pressure inside the stream is low? There is clearly something I don't understand here. I would like to know how to apply Bernoulli's principle correctly, and if possible, I would like to see a simple explanation based on Newton's laws instead of Bernoulli's principle.