Question

A common misconception about Newton’s first law is that when no net force acts on an object, the object must be at rest (i.e. stopped).

Here, we will illustrate an example that shows this conception to be false. When a skydiver jumps out of an airplane, she is initially in free-fall and therefore has a downward acceleration of one ‘g’ due to the force of gravity. As she falls, gravity speeds her up. But the faster she goes, the more air resistance impedes her motion by exerting an upward force on her. Eventually, her downward speed will increase until the downward force of gravity (i.e. her weight) is exactly balanced by the upward force of air resistance. At the precise instant these two forces come into and remain in balance, carefully and thoroughly explain why the skydiver does not instantly come to a stop even though the forces balance. So, what happens to the skydiver’s speed instead?

Answer 1

Here we apply Newton's laws of motion and definition of drag force.