Air Resistance

Question

1. Give three factors that affect the amount of air resistance an object experiences, and describe how each factor influences air resistance (will the air resistance go up, or go down if that variable alone were changed)?

2. Make a free body diagram for the falling filter for the moment just after you drop it.

3. Make a free body diagram for the falling filter for when it has reached terminal velocity.

Answer 1

The force of air resistance drag is proportional to the cross sectional area of the the object and to the square of the velocity at which it travels.   There is also a factor called the coefficient of drag Cd.    So three factors are:   cross sectional area, velocity and shape.     Cd is less for a cone than for a sphere.  That is why there is a nose cone on a rocket. 

 

In the instant just after drop, the only force acting is gravity (= mg) which acts downward.

 

At terminal velocity there are two forces which balance to a net zero.  The two forces are mg (downward as before) and the drag force acting upwards.  Their magnitudes are the same, their directions opposite.