The video mentions wind and breathing as two examples of pressure-driven flow, but other examples are all around you. Flows through pipes are almost always pressure-driven; think of firehoses, drinking straws, or blood vessels. What else can cause fluids to flow? One common cause is gravity. Rivers and streams are driven by gravity, and smoke rises because gravity pulls more on the cooler heavier air nearby. Flows can also be directly initiated by the motion of a boundary, such as when you stir a cup of tea or shake a water bottle.

Let’s return to wind for a moment. Wind is caused by pressure differences on the Earth’s surface, but how do these pressure differences get here? And how does the Earth’s rotation affect the wind? The details of wind can be very complicated, and some scientists devote their entire career to better understanding patterns in the wind. For more information about wind, check out this clip from Bill Nye’s episode on wind, or these diagrams from eSchoolToday about the sources and types of wind.

The video references sand grains on Earth and stars in the universe. Comparing these two quantities is a classic estimation problem and has been attempted by amateur and professional scientists for years. The question was made famous by Carl Sagan when he asserted that the stars were more numerous in this clip from his Cosmos series. Since then, other big name science enthusiasts have weighed in, including NPR’s Robert Krulwich and weblogger Randall Munroe.

OK so air is heavy. But is that just a neat factoid, or can we actually see the atmosphere’s crushing power in action? One of the easiest and most stunning demonstrations is the Incredible Can Crusher, an experiment in which you can crush a soda can using atmospheric pressure. Try it at home!

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