Drag versus Friction...

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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.

 

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.

 

 

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.

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