Air Resistance and Free Fall

Mar 07, 2020

This is a common question among many students-

Do heavier objects fall faster?

And this will be their general answer- “Yes.”

The above answer is purely a misconception. Well, this is expected because they are basing the information on a more practical sense.

You’ll see a stone drop faster than a piece of feather and naturally, you’ll come to the conclusion that heavier objects fall faster than lighter objects. After all, seeing is believing, isn’t it? But did you actually consider those surrounding factors associated with the experiment? Probably no! There are other factors at work as well, but you still came to the general conclusion of heavier objects falling faster than lighter ones.

The truth is that both objects fall at the same speed. Why? We’ll come to that.

Free Fall

A free fall is a special form of motion in which gravity is considered to be the only force acting upon an object.

When objects are in a state of free fall, they will fall under the sole influence of gravity.

All objects regardless of their mass will fall at the same rate of acceleration under such conditions.

Proof

Say, for example, you have an object A with a mass of 10kg and another object B having a mass of 1kg. The acceleration due to gravity is 9.8m/s2.

Force of gravity acting on object A= (10 x 9.8) N.

Force of gravity acting on object B= (1 x 9.8) N.

Calculating the acceleration of both the objects-

aA = (10 x 9.8)/10 m/s2= 9.8 m/s2.

aB = (1 x 9.8)/ 1 m/s2 = 9.8 m/s2 .

So you see that the rate of falls is the same in both cases. But why don’t we actually see that in action? There are several factors at play. One of them is air resistance.

Air resistance

When any object falls through the air, the object usually encounters a degree of air resistance. The resistance of air is a result of the collisions falling objects with air molecules.

The amount of air resistance is dependent on a variety of factors.  These two factors are:

  • Speed of the object,
  • Area of the cross-section of the object.

Air resistance is directly proportional to the speed of the object as well as the area of the cross-section of the object. With the increase in the speed of the object, the air resistance increases. The increase in the area of cross-section results in an increase in air resistance.

Final conclusion

If air resistance is absent, the rate of descent of the object is dependent on how far it has fallen. The mass of the object doesn’t matter in this case.

Thus, from the above statement, we can easily conclude that both objects would reach the ground at the same time when both of them are dropped from the same height in the absence of air resistance.

There is a famous hammer and feather drop experiment that was based on this exact topic. You can refer to the video below.

With that, we’ll sign off for now. I hope you had a decent read.

Article Posted in: Academics
Tags: Physics

Sudipto Das

Sudipto writes educational content periodically for LearnPick UK and backs it up with extensive research and relevant examples. He's an avid reader and a tech enthusiast at the same time with a little bit of “Arsenal Football Club” thrown in as well. He's got more than 5 years of experience in digital marketing, SEO and graphic designing.

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