Give examples please. Is air resistance harmful?

Answer 1

Air resistance is both helpful and harmful, depending on the circumstances.

If you are using a parachute to slow your descent while skydiving, then you need air resistance to work against the acceleration of gravity. In that case, it would be helpful.

However, if you were trying to reduce aerodynamic resistance (in a fast-moving car or airplane), then air resistance would be harmful. In a car, as it moves forward, the air pushes back against the profile of the car. This exerts a backward force, meaning that your car has to work harder to accelerate the faster it goes, because of the increase air resistance pushing back against the car. This is the reason why aerodynamics is so important in high-performance vehicle design.