## Questions/comments about labs

*Mon, Dec 11, 11:26 p.m.*-

**For lab #7, how can the curvature tell us whether or not the particle is positive or negative (especially for the outgoing particles). I tried to draw a tangent line to the curve but it did not seem to work, because I got the wrong answer.**

Positive charges curve one way, and negative charges curve the opposite way. So, here is what you do: for any labelled particle, look at which direction it is curving. Pretend that you are driving along the curve and ask yourself if you would have to turn the steering wheel to the right (curving to the right) or turn the steering wheel to the left (curving to the left). If it is a negative charge, then every other curve that curves the same way is also a negative charge, and any other curve that curves the opposite way is a positive charge.

And remember to figure out the direction of curving as if you are driving along with the particle.

*Thu, Dec 7, 4:37 p.m.*-

**Let us look at #2 for the checkout questions for Lab 1. I set up my F=ma-sub-x and F=ma-sub-y equations. I get -24.57 g = Mx and -163.15 g = My. If I find the magnitude of that mass, it is 164.99 g. This contradicts the problem statement giving the third mass as 239 g. Help!**

First, I'm guessing that you mean Lab 2 rather than Lab 1, correct?

Second, since this is static equilibrium, $\vec{F_{net}} = m\vec{a} = 0$ since nothing is moving. Here is how I would set up the problem:

$\Sigma F_x = ma_x = 0 \rightarrow m_1gcos(25^{\circ}) + m_2gcos(132^{\circ}) + m_{3,x}g = 0$ and that gives me $m_{3,x} = -71.1$ grams. Similarly, $\Sigma F_y = ma_y = 0 \rightarrow m_1gsin(25^{\circ}) + m_2gsin(132^{\circ}) + m_{3,y}g = 0$ and that gives me $m_{3,y} = -228.3$ grams. So, I get $m_3 = \sqrt{(-71.1)^2+(-228.3)^2}$ g or 239 g.

I'm not sure how you ended up with the numbers that you got, but hopefully if you compare with what I did, you can find the error.

*Sun, Dec 3, 6:36 p.m.*-

**Will there be labs next week.**

Next week is the ``open lab'' week. There is not a new lab, but the labs will be open if you want to go in and review them.

*Wed, Aug 16, 6:28 p.m.*-

**Hey everyone. <p>My lab is scheduled for 8:00 a.m. on Monday morning. Do we have lab on the first day of class?**

Yes! Labs start the first week of class. Make sure that you go.