TITLE: Why airplane wheels emit smoke on landing?
QUESTION [0 upvotes]: I've seen this phenomenon a lot of times but I can't give it a physically explanation. Someone has an idea?

REPLY [12 votes]: The wheels are not spinning while the plane is in the air.  At the moment that they first make contact with the ground, they skid a bit before they start rolling at a rotational rate consistent with the ground-speed of the plane.  That skid generates heat and burns off a little rubber. (This also accounts for the black smears on the runway at the point where planes typically first touch down.)
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