Rune wrote:
> 
> How can I simulate air resistance to the movement of an object? If the
> object is moving with the velocity V, what will happen to the velocity (or
> speed) over time? In which way will it decrease? Linearly, exponentially, or
> something different?

Well, a few years ago, some english chap name Newton came up with the
silly idea that a force apllied to an object resulted in a acceleration
proportional to its mass, of f=ma for short.

the force caused by air resistence is computed by the following formula:

F = (Cd)A(V^2) in the direction opposing the movement.

Where:
- Cd is the drag coefficient ( 1 for a box, 0.5 for a sphere and around
0.30 for most modern cars)
- A is the cross-sectional area of the object (area "facing" the air
flow)
- V is the speed of the object in that direction.

Provided that the shape and mass of your object dont change, you can see
that the force, hence the decelleration, will decrease at a rate which
is proportional to the square of the current speed.

> 
> Just to check if my general understanding of the terms is correct: I'd say
> that gravity increases the speed of an object linearly (assuming the object
> is falling downwards). Is that correct?

For all intents and purposes, let's say that the force of gravitation is
constant (the mass and size of your object are negligeable compared to
the mass and size of the Earth) and that the mass of your object is also
constant, hence the acceleration will be constant.  On Earth, it is 9.81
m/s^2 (or 32.2 ft/s^2 for the metric-impaired)

So yes, the downward velocity of your falling object will increase
linearly.

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