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# Physics: Drag Force

Written by Junsoo Kim

In grade 11 to 12 physics, we solved many problems assuming no air resistance. When we first learn projectiles, we know that our calculation is under the circumstance of assuming no air resistance. This assumption will lead to others wondering what happens if air resistance exists because drag force exists everywhere and can easily be felt.

The simplistic way to consider air resistance is through drag force.

Drag force is first dealt ion fluid dynamics. It has been introduced as a force acting opposite to the motion of an object moving. Drag force is only created if there is fluid. This concept sounds similar to previously learnt friction force. Considering drag force like fluid friction will help solve drag force problems. When drawing a free body diagram, drag force can be placed like friction force. Also, drag force requires the existence of fluid to be used, like friction force with friction. The main difference is that drag force dupes not have a difference in coefficient regardless of stationary or moving state. In friction force, it differs whether it is static friction force or kinetic friction force.

The equation for drag force is

F = 1/2 ρ v2CA

F means drag force, ρ means the density of the fluid, v means velocity, C means drag coefficient, and A means cross-sectional area. Another interesting fact is that the force is proportional to the squared velocity value and cross-sectional area. These relationships between force and other variables can provide more extensive insight into daily life examples such as swimming. When professional swimming athletes swim, they tend to wear clothes that are more attached to their bodies. This case can help reduce of cross-sectional area and less the drag force.