## Tuesday, October 30, 2012

### Using Energy Conservation for Finding Speeds

Generally we have two ways of determining the motion of objects - Newton's laws (F = ma) and energy.  Newton's laws are useful for finding accelerations and forces, but this can also be trickier since these are vectors, and for non-constant forces, we need calculus.  When we need to find speeds, I strongly recommend that you try energy to solve the problem.

Energy has the advantage that it is a scalar, so there are no vectors or components to worry about. We can also avoid calculus for NON-constant forces, such as springs and gravity.  Here are two examples with springs and gravity, and how energy conservation provides an easier, quicker way to get the speed.  Our starting point is:  Uo + KEo  =  Uf + KEf + heat, where heat is the work done by friction.

### NON-Gauss Problem: Find Electric Potential for Charged Sticks

Charged objects in real life generally are not in the 3 shapes we need for Gauss's law - spheres, long cylinders, or large plates.  Here, we look at how to set up the integrals necessary for finding the electric potential of charges sticks at arbitrary locations from the stick, where we do not have much in the way of symmetry to help simplify life.

The concept behind it is to break the problem into point charges.  The only thing we know exactly in electrostatics is how to deal with point charges, with E = kQ/r^2 and V = kQ/r.  So we need to break into point charges, find the small contributions from each charge, and add them all up, or integrate.  The one other piece of this so it works is to use a ratio of charge to length.  This allows for a substitution into the integral to make it solvable.

This video has two examples of sticks and finding electric potential.  I hope it helps!

## Saturday, October 20, 2012

### Congratulations to Seniors for their Research!

We just found out that seniors Laura Goetz, Sarah Posner and Marc Bouchet have been nationally recognized in the Siemens Science and Technology Competition, one of the biggest science contests for high schools.  Laura is a National Semifinalist, and Sarah and Marc, who worked together and are in the team portion of the competition, are Regional Finalists.  Sarah and Marc now advance to present their work at the University of Notre Dame in November, and are now in the running for large scholarships.  This is similar to what happened last year with Julia Crowley-Farenga and Patrick Loftus, who ended up winning a \$40,000 scholarship after placing 3rd in the country for their work in astrophysics.

Laura worked in the Prof. Morimoto lab at Northwestern, and her research, which looked at identifying genetic modifiers of polyglutamine expansion toxicity in Caenorhabditis elegans, has implications for Hutchingston's disease research.

Sarah and Marc studied properties of tandem organic solar cells that they made in the lab of Prof. Tobin Marks at NU, and worked under the mentoring of graduate student Nanjia Zhou. They are the only Regional Finalists from Illinois.

I also want to recognize senior David McDonald for his paper on the segregation and stratification of mixtures of different sized granular materials.  This work has implications for agriculture and new drug development.  David worked in the lab of Profs. Richard Lueptow and Paul Umbanhowar at Northwestern.

A very small percentage of students nationwide do high-level, independent research like this, largely because of time but also because it is difficult and must require countless hours of study and work in the lab, so these students need to be given some recognition for their efforts and contributions to several fields of science!  WELL DONE!!

## Monday, October 8, 2012

### Nobel Prizes Being Announced This Week

The 2012 Nobel Prize for Physics was shared by French physicist Serge Haroche and American physicist David Wineland (U. of Colorado at Boulder) for their work in controlling quantum superposition states.  This means they figured out how to study individual photons and individual atoms, respectively, which is really tough to do, as one might imagine.  This work could help lead to breakthroughs in the dream of developing quantum computers, which would theoretically be much faster and more powerful than today's best supercomputers.

The 2012 Nobel Prize for Chemistry went to two Americans, Robert Leftkovitz (Duke) and Brian Kobilka (Stanford).  These scientists have been instrumental in figuring out how cells are able to 'smell out' chemicals, allowing the cells to know what is happening in the environment and determine how to respond to the environment.

The 2012 Nobel Prize for Physiology or Medicine was shared by English scientist John Gurden and Japanese scientist Shinya Yamanaka, for their discovery "that mature cells can be reprogrammed to become pluripotent."  This is a big step for stem cell research because one does not need to rely on the controversial stem cells from embryos.  They showed that mature, adult cells can be forced to act immature again, as a stem cell, and then can be used to form any other cell of choice.  For years, embryonic stem cell research was politically, religiously and ethically charged because of the debate over when life begins.  This research allows scientists to largely avoid those questions and still do studies into how stem cells behave.