# Approaching Terminal Velocity

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1. Nov 21, 2014

### Peter Frame

Today in physics we talked about terminal velocity. This got me thinking. As air resistance acts on a falling object, the acceleration of that object will decrease. I was wondering if terminal velocity is only approached asymptotically and never technically reached. Please explain this. Thanks.

2. Nov 21, 2014

### phinds

Your question is a reasonable one, but no, terminal velocity IS reached. If the speed does not become constant, you have not reached terminal velocity. That's what the term MEANS. "Terminal" means "final" and is a value, not an asymptote.

3. Nov 21, 2014

### DaveC426913

Tilting my hat to phinds' answer, I guess that depends on how you look at it. Terminal velocity is not a fixed target, since it's dependent on many changing factors, such as orientation of the falling object.

4. Nov 21, 2014

### phinds

I see we disagree. I think you need to check the definition.

5. Nov 21, 2014

### Peter Frame

But if you graphed the velocity, it would curve to horizontal. Either midway along this curve it would suddenly flat line, or it would approach a number but never quite get there.

6. Nov 21, 2014

### Peter Frame

Also i meant this more as a conceptual question. In practice im sure it would reach a number.

7. Nov 21, 2014

### DaveC426913

And thus I have edited my response to account for that. :)

I think you're looking at it simplistically. Terminal velocity can't even be well-defined, since it's not stable.

8. Nov 21, 2014

### DaveC426913

It would approach a value and then wander up and down around as the orientation of the falling object changed from moment to moment.

9. Nov 21, 2014

### Peter Frame

So your saying that in a perfect experiment with no air current, and no wobbling object, it would approach it? This is what makes a lot of scene to me.

10. Nov 21, 2014

### phinds

Yes, I keep telling you, I am VERY simple-minded ;)

11. Nov 21, 2014

### phinds

I agree.

12. Nov 21, 2014

### phinds

No, in an ideal situation, it would reach it and stay there instead of reaching it and then, as Dave says, wobbling around a bit faster and a bit slower.

13. Nov 21, 2014

### DaveC426913

[EDIT Sorry, I did not see that you said an ideal experiment.]

Yes, so, to do so, you use an object that is stable under descent. Such as, say, a parachute.

A parachute, assuming its oscillation is kept down, reaches its terminal velocity quite quickly, and then its velocity will stick very close to that thereafter.

Last edited: Nov 21, 2014
14. Nov 21, 2014

### Peter Frame

Thanks

15. Nov 22, 2014

### Danger

Are you getting old? Your text is starting to turn grey...