SAT II Time!!

For those seniors who are planning on taking the SAT II Physics Subject Test, we will begin some lunch time reviews soon.  The lunch reviews will focus on some optics, magnetism and electromagnetism.  We will do this a few weeks before you take the October test, so you will also have a couple weeks to practice and ask questions.  We will discuss this in class when you come into physics.

However, in the mean time, there is a really nice site for the SAT II Physics on SparkNotes.  It has explanations/notes on each topic, practice questions, and solutions for all questions, as well as strategy and what to expect on the SAT II.  As with other tests, there will be a curve, with a top score of 800 possible.  More to come on this, but definitely start checking out the web site so you can be reviewing.

How to do Vector Multiplication: Dot and Cross Products

There are times when we will have to multiply two vectors together to define some third quantity.  The strange thing is, there are two ways we can multiply vectors - one where we get a scalar for an answer, and a second where we get a new vector for an answer.  These are called dot (or scalar) products and cross (or vector) products, respectively.

Dot products have two ways of being calculated, and choose the method that makes it easier based on the information given in the problem.  Cross products are a bit more involved and require a 3x3 determinant to figure out the x, y, and z components of the new vector.

Geometrically, dot products multiply the two parallel components of the two vectors.  The formula, if we know the magnitudes of the two vectors, is A dot B = ABcos(theta).  And cross products multiply the two perpendicular components of the two vectors, or A x B = ABsin(theta).  In these definitions, theta is the angle between vectors A and B.

Electron Micrographs of MANY Things

This is a page of beautiful photos (over 1100) from electron microscopes.  It shows some fascinating structures, and also the beauty and complexities of Nature. Check it out at:
http://www.flickr.com/photos/fei_company/

Pretty Cool Animation of how a Digital Camera Works

This is a short and sweet animation of a Nokia digital camera.  See if you can identify the various steps in the process.

How to Use Tracker Video Analysis software

Every do often, we may be doing data analysis of events recorded by video.  This might be a ball thrown through the air, a video game, a cool YouTube video you find, or anything that has motion involved.  The goal is to get your data from the video.  We will have three main ways of doing this.

One way is a scaling exercise.  Quite literally, you can measure the sizes and distances on the computer monitor.  If you know the actual size of on object in the video (perhaps a person or meterstick), you can scale lengths of any other object in the video to get its size, or to measure the distance the object moves.  The other quantity we need is time.  This will require either timing the event on the video, which could include just reading the time stamp of the video or timing with a stopwatch if the video is running in real time.

The other two methods are very similar, and use software.  Logger Pro, which is the software we use to run our Vernier sensors, and Tracker, a free online program, can have any video on your hard drive imported for analysis.  It is really cool stuff, and below is a video that explains how to use Tracker to get data from a video where a ball is tossed in the air.  Watch and learn, and then you will have chances to do this with any video we use during the year (or better yet, on your own when you are curious about something you capture on video).

Keep in mind, you can upload video from a camcorder or your cell phone onto your computer.  What about if you want to analyze an existing YouTube video, or if you want to analyze an online video game?  You will need to make a screencast video and save it on your computer, and then import that video file (recommend MP4 video) into Tracker or Logger Pro.  The easiest way to make a screencast video is Screencast-o-matic.

Former Chem-Phys Student Featured in Wired, for Skybox Start-up

Dan Berkenstock, a former ETHS student who came through Chem-Phys, is now a VP at Skybox, a start-up technology company in Silicon Valley.  Skybox is getting good press in Wired magazine, which describes the mission of Skybox here.  Skybox is building a satellite network that will be able to take high resolution photos all around the Earth, and use the vast amount of data in those photos to companies, governments, and so on.  With only about a dozen satellites currently able to do this, Skybox is going to, perhaps, corner this market.  There could be enormous financial rewards waiting if successful, so time will tell.  But keep in mind Dan used to sit in your seats, so this shows one path for your young, creative minds!

A really cool demonstration of momentum and energy.  Try to understand this one!  Where can we get long bead chains like this?!?!?!  We must try this one in class.

TED: Freeman Hrabowski and his 4 Pillars of College Success

A talk from the President of University of Maryland, Baltimore.  He marched with Dr. Martin Luther King as a boy, and now works on getting minorities, the poor, and other underrepresented groups into science and math.

Video for an Explosive Use of Capacitors and Conservation of Momentum, Watermellon style!

Courtesy of Louis S.:

The video I chose actually represents two aspects of physics in this class.  The set-up of the watermelon explosion is simply a large bank of capacitors wired together in series with an extremely high voltage. When one of the capacitors is discharged, there is an enormous current that runs through the watermelon, causing it to explode. This shows the relationship between capacitance, voltage, and current.  The other portion of this class can be seen with the high speed camera showing the watermelon explode.  When the watermelon is initially at rest, its momentum is zero.  Then, once it explodes, all of the little pieces of watermelon-shrapnel must fly off such that the components of their motion must equal zero.

Congratulations to the Class of 2013!! You will be missed

Each year this is a bittersweet time for me.  I hate to see the senior class leave, but at the same time I am tremendously happy for and proud of the students.  You are about to enter a new phase of life, and also one of the great times in life.  You are all prepared for college on the academic side, and you will quickly learn and adapt to independence on the personal and social sides.  Enjoy the experience!

Here's to the Class of 2013!  A job very well done!!
- Doc V