Drag
versus Friction...
The Wrights understood that airplanes with very
little drag generate the same amount of lift with less thrust. They knew that
aircraft with very little drag required less thrust to fly. Drag is unwanted
because planes with more drag require more thrust to fly.
Friction is the rubbing between solid
objects. For instance, when you rub
your hands together you will feel friction, the force that resists motion and
creates heat. Friction can be used for positive purposes: athletes wear
sneakers on a gym floor so that they don't fall down while running. However,
because friction is not wanted in a machine like a bicycle, oil is used to
minimize friction.
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Drag is the friction between a solid
object and a liquid or a gas. For
instance, when you sail a boat across a lake, the force that resists the movement
of the boat through the water is drag. Heat is generated by drag just as heat
is generated by friction. |
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When you ride a bicycle at high speed,
drag makes the bike harder to pedal and increase speed. Racing cyclists crouch
over their handlebars to decrease drag and increase speed. |
There is a difference between drag and
friction. Friction is relatively constant at different velocities while drag
increases with speed. For example, when you rub your hands together at different
speeds, the force of friction remains the same although the heat generated will
vary. In contrast, as you increase the speed of your bike, the drag increases
significantly.
To decrease friction in machinery, low-friction materials such as Teflon and other plastics are used. Contact surfaces are designed to be smooth as possible. Lubricants are introduced to reduce friction.
To decrease drag on an airplane, smooth surfaces and a streamlined design are used. In addition, high aspect ratio wings are used as well as an optimum camber.