image credit: Ed Lee
Demonstration of Aneurysms
How is an artery like a balloon? The photo (larger version) shows two partially inflated modeling balloons--the balloon begins to inflate at a weak point along its wall, and the wall bulges out, decreasing the pressure inside. For a discussion of this effect, including a video showing how the pressure in a balloon changes as it inflates, visit Demonstration of Aneurysms from Cambridge University. The same bulge happens in arteries--see the PBS site Aortic Aneurysms. To learn about the physics of elasticity in balloon walls, see Wall Tension from Hyperphysics.
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Partly inflate a cylindrical balloon so that a nipple remains on the uninflated end. Press each part of the balloon. Is the air pressure the same everywhere inside? Pascal's Principle says yes--otherwise air would flow from high pressure to low pressure. When you press, could the stretched skin of the inflated balloon be putting a force on your finger? See Wall Tension from Hyperphysics.