# B Acceleration and Gravity

#### BRH

I know that there is constant acceleration due to gravity. A regular force that is applied to a moving object causes the object to accelerate once and as long as the force is present. Meaning, if a ball that is rolling experiences a wind force of 5N the ball's movement will increase 2 mph for example... as long as the wind force is present. Why is it that by gravity the falling object keeps on accelerating every second 9.8m/s. Why doesn't it just accelerate once 9.8 and that's it, until reaching terminal velocity?

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#### BRH

How is it that by a falling object if the object doesn't reach terminal velocity, it always falls with acceleration of 9.8m/s. It doesn't matter if the object has a gravity of 5N and air resistance of 4N or if the object has a gravity of 5N and air resistance of 1N... Why doesn't air resistance make a difference as to how much the object will accelerate?

#### berkeman

Mentor
I know that there is constant acceleration due to gravity. A regular force that is applied to a moving object causes the object to accelerate once and as long as the force is present. Meaning, if a ball that is rolling experiences a wind force of 5N the ball's movement will increase 2 mph for example... as long as the wind force is present. Why is it that by gravity the falling object keeps on accelerating every second 9.8m/s. Why doesn't it just accelerate once 9.8 and that's it, until reaching terminal velocity?
How is it that by a falling object if the object doesn't reach terminal velocity, it always falls with acceleration of 9.8m/s. It doesn't matter if the object has a gravity of 5N and air resistance of 4N or if the object has a gravity of 5N and air resistance of 1N... Why doesn't air resistance make a difference as to how much the object will accelerate?
Welcome to the PF.

Air resistance does affect the total acceleration of falling objects in an atmosphere. It is a retarding force, The sum of the two forces (gravity down and air resistance up) gives the total force and thus the total acceleration by Newton's Law:

ΣF = ma

#### davenn

Gold Member
How is it that by a falling object if the object doesn't reach terminal velocity, it always falls with acceleration of 9.8m/s. It doesn't matter if the object has a gravity of 5N and air resistance of 4N or if the object has a gravity of 5N and air resistance of 1N... Why doesn't air resistance make a difference as to how much the object will accelerate?
Air resistance does affect the total acceleration of falling objects in an atmosphere. It is a retarding force, The sum of the two forces (gravity down and air resistance up) gives the total force and thus the total acceleration by Newton's Law:
..... and when the 2 forces are equal ... the upwards force of the air resistance Vs the downwards force of gravity ....
then the total force = 0 (zero) and with zero force, there is zero acceleration and hence a terminal (fixed ) velocity

Dave

"Acceleration and Gravity"

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