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legal
guide to UK motoring, sections for law enforcement, Driver licensing,
learner and new drivers, buying and selling, speeding fines, owning a
vehicle, wheel clamping, traffic information
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Danger: Smooth Road Ahead
Where
the rubber meets the road, odd and dangerous things can
happen. On wet asphalt at high speeds, for instance, or
on a flooded surface at just about any speed, a car tire
can hydroplane, skidding along on a thin sheet of water.
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But skidding can happen on roads that are not as wet and at
lower speeds, and scientists have never been able to fully explain
the loss of friction that occurs under those conditions.
Now a team of scientists in Germany and Italy has come up with
an explanation. Water becomes trapped in the asphalt, and the
rubber of the passing tire effectively seals it in place. This,
they write in the journal Nature Materials, has the effect of
smoothing the road surface, reducing friction.
Even the smoothest-looking asphalt road has tiny peaks and valleys
in the surface. Under dry conditions, the rubber of a tire will
deform slightly as it penetrates the valleys and then hits the
peaks. These pulsating deformations, multiplied countless times
as the tire moves along, create a lot of friction.
When the asphalt is wet, however, the valleys become tiny lakes.
The passing tire can't deform into the valleys because the water
is there, and it can't push the water out because the rubber
hitting the peaks forms a seal.
So the road, in effect, is smoother - there are fewer deformations
and thus less friction.
The researchers say their calculations can account for the 20
to 30 percent loss of friction that occurs at low speeds (below
about 35 miles an hour) on wet but unflooded roads.
Article written By HENRY FOUNTAIN |
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