# Air drag force: Why heavy objects accelerate faster?

• babaliaris
In summary, the conversation discusses the acceleration of two objects in free fall without a drag force. It is mentioned that the acceleration does not depend on the mass of the object and both objects will reach the ground at the same time. However, in real life, the heavier object will accelerate faster. The conversation then goes on to explain the math behind this and how it can be used to explain things in physics. It is noted that the initial assumption of constant acceleration was incorrect and will need to be adjusted in the future.
babaliaris
I've done the math but because i can't find this answer anywhere in the book which I'm reading and on the web, I would like to be sure if my calculations are correct. I know that if two objects (starting at the same time) are free falling without a drag force being applied to them, the acceleration is:

Which means it does not depend on the mass of the object. So the two objects no matter their mass, will accelerate with the same magnitude and they will reach the ground at the same time.

On Earth,if you see two objects free falling, the heavier one will accelerate faster. So let's see what maths can tell as by applying Newtons second law:

C = coefficient of air's drag force.
P = air's density
A = the area of the free falling body.
V = the velocity of the free falling body.
D = Drag force.
Fg = body's weight.

Be aware that we don't have an initial velocity.

So if we assume that we are leaving two objects with the same Area (A) (a metal block and a leaf) and the metal's mass >> leafs mass , the above formula explains why the metal block will accelerate faster (numerator is big if m is big so does the acceleration).

By the way the maths which i did above, until today, i didn't know that you can use maths to explain things in such a way. I started reading classical physics 3 days ago and they already made me understand how you can use mathematics to explain things! Literally, i didn't know i could use maths in such a way! I only knew how to solve exercises and nothing more! I love physics!

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Last edited:
Drakkith
Unfortunately, it is not correct. You have assumed that v = at, which is only true for constant acceleration and an initial speed of zero.

babaliaris
Orodruin said:
Unfortunately, it is not correct. You have assumed that v = at, which is only true for constant acceleration and an initial speed of zero.
Yes you are right... The book didn't told me yet, but as I can see the acceleration in this situation is not constant. So I have to wait until I learn about varying accelerations in motion and redo it.

## 1. What is air drag force and how does it affect the motion of heavy objects?

Air drag force, also known as air resistance, is the force exerted by air on an object as it moves through the air. This force acts in the opposite direction to the object's motion and can slow down its acceleration. Heavy objects experience a greater air drag force than lighter objects, which can result in a slower acceleration.

## 2. Why do heavy objects fall faster in a vacuum compared to in the presence of air?

In a vacuum, there is no air resistance, so the only force acting on an object is gravity. This means that all objects, regardless of their weight, will fall with the same acceleration, known as the acceleration due to gravity. However, in the presence of air, heavier objects experience a greater air drag force, which can slow down their acceleration and make them fall at a slower rate.

## 3. Can air drag force be completely eliminated?

No, it is impossible to completely eliminate air drag force. However, it can be reduced by changing the shape or surface of an object to make it more aerodynamic. For example, a streamlined car will experience less air drag force compared to a box-shaped car, resulting in a faster acceleration.

## 4. How does air density affect air drag force?

Air density is a measure of how many air molecules are present in a given volume of air. Higher air density means there are more air molecules that can collide with an object, resulting in a greater air drag force. Therefore, in denser air, heavy objects may experience a greater air drag force and have a slower acceleration compared to in less dense air.

## 5. Is air drag force the same for all objects?

No, air drag force can vary depending on the shape, size, and surface of an object. For example, a smooth, streamlined object will experience less air drag force compared to a rough, irregularly shaped object. Additionally, the speed at which an object is moving can also affect the magnitude of air drag force.

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