# Question #6527a

Apr 20, 2017

There are two forces acting on a falling object:
gravity and drag (air resistance).

#### Explanation:

If it were only for gravity , the object would at any time have a speed of:
${v}_{t} = {v}_{0} + g \cdot t$
where:
${v}_{t} =$ speed at time $t$ in m/s.
${v}_{0} =$ starting speed (=0 if just falling)
$g =$accelaration of gravity ($\approx 9.81 m / {s}^{2}$)
$t =$time in seconds.

Drag is an opposing force, that depends on shape, surface area and speed. Usually it is in ratio with the square of the speed, which means that it rises quadratically with speed.
Thus when an object falls, the gravitational force ${F}_{g} = g \cdot m$ remains constant, while drag rises. There will be a moment when both are in equilibrium, and no more acceleration occurs.
The object is now at terminal velocity.