## jk_16 3 years ago in air resistance (drag) is acceleration constant??

1. alexray19

Yes, it is a force. But its magnitude, direction, behavior, etc is a function of several other variables related to the nature of the object experiencing the resistance (e.g. its shape, velocity, its environment, the properties of the air, etc).

2. vf321

What do you mean? Acceleration has no influence on drag force, so $$\frac{dF_{drag}}{da}=0$$ , but it has an influence on the acceleration since it's a force.

3. vf321

***Instantaneous acc has no influence on drag

4. alexray19

Assuming ceteris paribus, as an object travels at a constant velocity in a straight line through non-turbulent air, it experiences a constant acceleration backwards caused by the air.

5. jk_16

the grap of a v-t system under the influence of air resistance..is not a constant v(t)

6. vf321

grap?

7. alexray19

That is, in order to maintain constant velocity, the object must constantly be accelerating forward with a force equal but opposite to the force caused by the air resistance. It's like driving your car at high speeds; you have to constantly give it some gas to maintain your velocity, which is goes against Newton's law that an object in motion remains in motion. The resistance caused by air (and internal friction) accounts for this need to constantly accelerate the car.

8. vf321

If an object is ONLY encountering drag, $F = \frac{1}{2}cAv^2$$m a = \frac{1}{2}cAv^2$$k=.5cA/m; \frac{d v}{dt}=kv^2$

9. jk_16

@vf321 where did you get the initial F=1/2 cAv^2 from

10. vf321

That's the formula for drag, if I remember correctly.

11. jk_16

how do i derive it?

12. vf321

derive what

13. jk_16

F=12cAv2 ma=12cAv2 k=.5cA/m;dvdt=kv2

14. vf321

Well u just did it...