Thanks to Michael who found this article. Pretty timely as we begin magnetism!
Check out http://arstechnica.com/science/news/2012/01/galactic-magnetic-fields-produced-in-a-lab-using-lasers.ars?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+arstechnica%2Findex+%28Ars+Technica+-+Featured+Content%29 to check out the latest experiments that deal, in the lab, with galactic strength magnetic fields for protostars and galaxies. Technologies like this will open up new experimental paths in astronomy, where, of course, it is difficult to experimentally test theoretical predictions since we cannot just go out and begin measuring stuff on a galactic scale! This also helps us realize how much more we have to learn and test in the sciences...we will never be able to find final answers to this crazy universe.
Sunday, January 29, 2012
Sunday, January 22, 2012
The solutions for the energy review set last Thursday are at http://sp.eths.k12.il.us/vondracekm/Shared%20Documents/Forms/AllItems.aspx.
Saturday, January 21, 2012
Any time we have a circular motion problem for some object, we need to think in terms of using our generic mv^2/R for the net centripetal force. As always, draw the force diagram. But this time, also note where the center of the circle is, and draw in the radius line. Use the picture to set up the math! Anything that points along the radius towards the center is a positive centripetal force, and anything that points away from the center is a negative centripetal force (i.e. centrifugal force). Check out both horizontal and vertical examples.
Thursday, January 19, 2012
Today, make good use of time to hit energy topics. The big ideas include kinetic and potential energies, that relationship between force and potential energy, F = -dU/dx, which is used with potential wells, and work. Power is also fair game. There are videos for potential wells, gravitational energy, and springs (elastic energy). You will also get a review set. For the 3-4 class, keep in mind the addition of rotational kinetic energy for rotations.
Wednesday, January 18, 2012
Here is a quick video discussing the topics for the final. In particular, motion and Newton's laws. Keep in mind all the resources you have available. Quizzam solutions are all on my school website, notes and Princeton Review materials, and of course Moodle with all the old AP exams and solutions. There are also 5 old multiple choice exams on Moodle. Be productive today, and try the review set together. Keep in mind that for the final you will be responsible for things like the derivation for air friction - there is a how to video for both the hockey puck and sky diver examples. There is also a how to video for systems (tension problems). I hope all this helps!
Sunday, January 15, 2012
Here is another example of a NON-Guass's law problem, a partial ring of charge. This is a combination of sticks and rings, the two classic cases where we might have to calculate something like an E-field or potential on some axis. In any case like this, we need to use the fundamentals: point charges, which we know how to do exactly. We break the problem into a bunch of little charges, find the small contribution, and then add them all up using an integral! Let's check it out, and I hope it helps.
Gauss's law provides a relatively easy way to find E-fields for charged spheres, long sticks or cylinders, and large plates. The last two, of course, are approximations in the end, but ends, edges, and corners really make for a difficult math problem. When stuck with such a problem, we have no choice but to stick (heh, heh) with the fundamentals. That is, point charges. We know how to handle point charges, and physically that is all a charged object is - a bunch of extra charged particles. So we need to set up an integral and add up a bunch of small fields or potentials! Check it out.
Monday, January 9, 2012
Here is a case where we have vertical circular motion, a pendulum or swing, where it is a bit more complicated than horizontal circular motion. For a pendulum, the tension and gravity components vary with the angle, so we have non-constant forces and acceleration. This could be tough to solve with Newton's laws. However, with energy we can find speeds more easily, and this will allow us to find the tension in the string for any angle of its motion. Check it out.
Wednesday, January 4, 2012
MIT and several other powerhouse colleges have, for years, had free courseware for many of their classes. Now, MIT is offering access to interactive courses FOR FREE to anyone on the planet! This is to be called MITx. You will not be able to get an MIT degree, but this will provide ANYONE the highest-level supplements in any subject you are interested in! New resources that will become available for education will be amazing! Can't wait to see what this is like.
Hopefully, good news. A number of students have asked if and when how-to videos would re-appear, after they all disappeared last spring when the company that stored them went under. Slowly but surely they are coming back. Check out the List of all how-to videos and check out those with the 'On YouTube' note. I'm trying to get those that are relevant for exams back up first. Thanks for your patience, and I really hope these help!!