# Do heavier masses experience greater air resistance?

Discussion in 'MCAT Study Question Q&A' started by m25, Sep 4, 2014.

1. ### m25

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Do heavier masses experience greater air resistance?

My EK 1001 physics book is telling me that force of air resistance is not dependent on the mass of the object, since force of air resistance is only proportional to (density of the medium)(surface area of the object)(velocity of the object)^2

Yet, because heavier masses reach a higher terminal velocity, wouldn't the velocity of the object increase, thus increasing the force of air resistance?

2. ### Cawolf 5+ Year Member

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Force Drag = F = o.5*rho*v^2*C*A

So the drag force is proportional to the density of the medium, speed of object, shape, and cross sectional area - not the mass.

The terminal velocity formula is derived from when the drag force is equal to the fore of gravity. This will include the mass of the object.

So drag force not effected by mass, but terminal velocity is.

3. ### Marleywh

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Heavier masses don't reach higher terminal velocities.

4. OP

### m25

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They don't?? I thought the terminal velocity was proportional to mass/(area)(density), so more mass, higher terminal velocity.

5. ### Marleywh

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Hmm I don't know that formula, but no, two objects of the same volume and shape will have the same terminal velocity through the air. Think about why something reaches terminal velocity. If it has stopped accelerating, that means that the net forces on the object are zero. So the force of gravity has equaled the drag force of the air. What has more drag, a metal ball, or a kite? Now what if you had a metal ball, and then you took another metal ball of the same mass, and stretched it out into the shape of a kite. Even though they are of the same mass, the kite shaped one will have much more drag and will have a lower terminal velocity.

This is all due to air resistance. In the absence of air (on the moon for instance), all objects fall at the same rate, regardless of mass or shape or volume.

6. ### Cawolf 5+ Year Member

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Sorry @Marleywh but that is incorrect.

In the presence of air resistance, the heavier object will reach a greater terminal velocity if all other factors are the same. Do the math and see.

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7. ### Marleywh

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Oh wow I guess you are right. Weird...

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