# Acceleration in terminal velocity?

1. Feb 7, 2016

### calculator20

I've just read somewhere that acceleration is zero when an object is at terminal velocity? I think it's wrong but wanted to check if I'm right?

Yes the resultant force is zero but gravity doesn't disappear so presumably acceleration due to gravity is constant? Terminal velocity means constant velocity and therefore constant acceleration?

Using F=ma to make F cancel upwards and downwards if mass is constant then does this mean the deceleration caused by air resistance equals acceleration due to gravity?

Many thanks

2. Feb 7, 2016

### Orodruin

Staff Emeritus
No, you are wrong. The resultant force is zero and therefore acceleration is zero. If this was not the case the velocity would change and therefore not be terminal.

Yes there is acceleration from gravity, but it is exactly canceled by the acceleration from air resistance. Constant velocity means zero acceleration.

3. Feb 7, 2016

### A.T.

Yes, constant acceleration of zero.

4. Feb 7, 2016

### calculator20

Ok yes understood. That aside is acceleration zero for terminal velocity? I don't think it is?

5. Feb 7, 2016

### ZapperZ

Staff Emeritus
Did you read and understood the replies you received in Msg. #2 and #3? I don't know if you can get a clearer and more definitive answer that what you had already received. If you didn't understand even something as direct as those, what could someone else saying the same thing be any different?

Zz.

6. Feb 7, 2016

### calculator20

Ok thanks for your help

7. Feb 7, 2016

### calculator20

No they hadn't appeared when I responded, not sure your abrupt response was entirely necessary!

8. Feb 7, 2016

### Staff: Mentor

If posts #2 and #3 hadn't appeared when you responded in post #4, what exactly were you responding to?

That aside, do you still have questions about why acceleration is zero at terminal velocity?

9. Feb 7, 2016

### Staff: Mentor

Not really.

EDIT -- Actually, that is a funny typo you made!

Last edited: Feb 7, 2016
10. Feb 7, 2016

### Staff: Mentor

Why do (or did) you think it isn't? Then people can address that, if necessary.

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