Flight -

Drag and friction
There are certain forces that oppose the movement of high speed vehicles through the air. Drag and, in the case of cars, friction are two forces that oppose the force of thrust of the vehicle. We can minimise friction by having proper lubricants on all the joints of our vehicles. Drag is somewhat more difficult to eliminate. The faster a vehicle goes the greater the force of drag becomes. Try running in water knee deep. If you walk slowly the force of drag is not as great, but try running and you soon notice this almighty force, we call drag, impeding your movement through the water. There are 4 forms of drag.
*Parasite drag* – this comes about due to structures protruding from the vehicle. These structures smash against air molecules and obstruct the movement of the vehicle. Fins on a rocket are a good example of parasite drag.
*Friction drag* – the surface of any object is full of microscopic valleys and hills. As air molecules move past the surface they strike these valleys and slow the vehicle down.
*Pressure drag* – this is caused when air molecules strike the oncoming surface of the vehicle. Rockets minimise this form of drag by having a pointed nose. Cars have rounded bonnets to force the air to flow over the surface smoothly.
*Base drag* – is caused when there is a large surface area at the rear of the vehicle. Once again you will notice rockets taper towards the end. As the air flows over the edge of the base it creates a vacuum which sucks the air into it as well as the vehicle. So the vehicle is always fighting to overcome this suction. This can be minimised by reducing the surface area of the rear of the vehicle.
Discuss situations where friction is important in our every day life. Where is high drag necessary and desirable? Design a car, describe ways in which your car design can reduce the four forms of drag.