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. To learn about the physics of elasticity in balloon walls, see Wall Tension from Hyperphysics.

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Wall Tension

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.

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image credit: Arindam Chaudhuri & Wellcome Images; image source

Artery Under Stress

This image (larger version) shows a three-dimensional model of an aneurysm in a human patient.  An aneurysm is a ballooning of an artery at a weak point (see Physics in Your World).  The model was made of latex, inflated with a liquid, and photographed in polarized light. For the physics of aneurysms, see Danger of Aneurysms (scroll down to the bottom) from Hyperphysics.

The Baby's First Breath

Physics is important from the moment of birth.  To find out why elasticity makes it hard for a baby to inflate its lungs, see the Hyperphysics page The Baby's First Breath. On the same page, scroll down to find out why large arteries needs thick walls but capillaries can be extremely thin. For more on the lungs, check out Alveoli of the Lungs.