[Physics] Does Polytetrafluoroethylene (Teflon) have low wind resistance


It is reasonable to assume that covering for example an airplane with Teflon would lead to it having lower wind resistance? The reason why I ask is that Teflon "has one of the lowest coefficients of friction against any solid." according to Wikipedia.

Best Answer

The resistance to flow through air is not the same as the coefficient of friction.

When air is flowing over a surface the flow is generally laminar very near to the surface, though it may be turbulent further away from the surface. Anyhow, in laminar flow the air immediately next to the surface isn't moving. The air doesn't flow by sliding over the surface, it flows by shearing the layers of air near the surface. There is no "frictional sliding" analagous to two solids sliding over one another, so there is no concept of a friction co-efficient.

Now to Teflon. You need to be very careful when talking about Teflon having a low friction. It has a low surface energy, so other materials tend not to adhere to it, and it's the adhesion between surfaces that is the physical origin of friction. This adhesion may be Van der Waals forces, dipolar forces or even chemical bonding, and Teflon is non-polar and chemically inert hence the low adhesion.

But outside the laboratory friction has various components. In particular you get energy losses due to plastic deformation in the surfaces that are sliding over each other, and this manifests as a frictional force i.e. the energy loss means you need to do work to slide the surfaces. Teflon dissipates more enery in this way than e.g. glass, so the friction is not necessarily lower than e.g. glass with a good boundary lubricant.

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