Wednesday, November 23, 2011

The Physics of Whipped Cream


There are two physical principles involved in making the delicious white fluffs (the canned ones).

First is the liquefied gas. When the canned whipped creams are made, half the bottle is filled with cream (although these days it’s usually hydrogenated vegetable oil) and the other half of the bottle is filled with liquefied gas. To liquefy gas at high temperature, great pressure is applied to the gas and consequently the pressure inside the can is much higher than the pressure outside of the can. The liquefied gas mixes with the cream inside the bottle, and when we tweak the valve, which works to equalize the pressure inside and outside the can, the pressure inside the can decreases and some of the gas evaporates, making a gas layer on the top of the can. This layer takes up a large volume and pushes the liquefied gas + cream through the tube, out of the can. When the liquefied gas inside cream comes out of the can and experiences sudden increase in pressure, they also evaporate, making air bubbles. These air bubbles are trapped inside the cream, making the cream fluffy. (Disregard the numeric values on the graph).
Second phenomenon is the “sheer thinning.” The whipped cream when it’s coming out of the can flows out like liquid but once it sits on top of the whatever drink you have, it stays put like solid. This is because when the molecules of the cream slide or “sheer” past each other, the viscosity of the liquid decreases temporarily and the cream flows. This phenomenon was demonstrated by NASA in 2008. NASA used xenon, which is a chemically inert, sing-atom substance, in outer space because the experiment needed xenon to be at its critical point where the line between liquid and vapor states blur.  NASA demonstrated that when they stirred the xenon fluid faster, the resistance to stirring decreased, which indicated that the viscosity of the fluid has temporarily decreased. - Post written by Eunnie Jung

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