Air Resistance and Terminal Velocity

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This is a basic physics tutorial that is targeted at GCSE (grade 9 and grade 10) standard reviewing the friction forces involved in air resistance and terminal velocity. The video for this written tutorial is on its way.

What is air resistance?

Air resistance is a type of frictional force that occurs between gas and the surfaces of solids. It's not very noticeable on a fine day if you're walking in the park. Instead it is most evident when either the solid, the gas, or both are travelling at high speeds.

For example, cars travelling at high speeds will experience significant air resistance. The faster the speed, the more air resistance experienced. Significant air resistance increases the amount of power and fuel needed to travel at a set speed.

Engineers design cars to not only look good, but to also reduce air resistance; this makes them more fuel efficient. In general, curved narrow surfaces experience less air resistance than straight or wide surfaces. These considerations are essential components of aerodynamic design for airplane designs.

When is air resistance useful?

Air resistance is particularly useful for parachuting. When a person jumps out of a plane, they will be in free fall. The gravitational pull of the earth will pull the person downwards, with increasing acceleration. Consequently, their speed of descent will increase initially.

As they gain speed however, air resistance will also increase. Eventually, the two forces (gravity and air resistance) will balance and the person will descend at a constant speed. This constant speed is known as terminal velocity.

If the person was to continue travelling at this speed towards the earth, the impact with the ground would kill them. This is why we use parachutes.

Parachutes are designed with a large surface area in order to take advantage of air resistance. By doing this, they slow the person attached to them down. So long as a person opens their parachute with enough time, they will negatively accelerate (i.e. slow down) from their terminal velocity to a safe landing speed.

Does air resistance ever disappear?

Air resistance occurs because objects moving through air need to move the air molecules aside as the object travels. In instances where there are no air molecules, there is no air resistance. The best example of this is in space, where there is no atmosphere.