AP Physics B Test - Torque Help?

[sapphic_yellow]

I'm taking the AP Physics section B test in about an hour (good luck to anyone taking that), and I have a relatively simple question to ask that I hope I can get answered in that time.

In torque, why was torque established to be positive in the counterclockwise direction and negative in the clockwise direction? Is there some deeper reason for this or was it just a standard that was set up in an experiment, such as Franklin's early use of conventional current? And if this supposition was based off an experiment, what experiment was this?

Lots of thanks for any help,
sapphic_yellow

(Any wishes of good luck would be nice too. I'm scared to death.)

 

[whozum]

They don't have to be that way, you can set them any way you want as long as you keep the system consistent, but I really doubt something like that would be on your test.

 

[sapphic_yellow]

In every review book I've seen, they'll have answers with the correct magnitude but different signs, and the correct answer is the one calculated using positive as counterclockwise. Also, both the book we use (Giancoli) and my teacher stated in that particular unit that positive was counterclockwise, but it was never explained why. However, I've been told that on the test there are some questions about experiments and such, so I'd like to know if there is some sort of basis.

And hey, go Arizona. Me too.

 

[bross7]

I believe it is just an accepted principle. When the Earth was determined to spin counter-clockwise this was given a positive value, so it is possible that it stemmed from this.

 

[p53ud0 dr34m5]

heh, saphic_yellow. how did you think of the physics exam. i took it. i didnt think it was bad at all. unfortunately, when i view a test as easy, that is usually not the outcome. I am too impatient to test. i hope you did well, though.

 

[ericarnold86]

I took AP B as well... On all the practice, I usually get between 50-65 of the multiple choice right, and i thought this was pretty easy. However, the free response was tough imo... The kinematics, lab, pendulum, and PV=nRT were pretty reasonable, but the density/volume/buoyancy one, the quantam theory one, and charge one were sort of pains. The charge one, once you got into it, was workable; I just left it for last and ran out of time.

 

[sapphic_yellow]

To you two who both did the AP Physics B test -
I sucked. You both probably did quite a bit better than I did. I did quite well on the multiple choice, but on the free response, four out of the seven questions were on material we had never covered in class. Last year, the school cut the alloted class time for AP Physics from two consecutive periods to just one, so the professor was able to cover only about three quarters of the required material, and we did no labs. Got an unlucky draw, I guess. Good luck to both of you on your scores.