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Saturday, January 31, 2015

49 Reasons I got into and love Teaching - In Honor of my 49 GTP Finalist Colleagues!

In late January, 1995, just having completed my Ph.D. defense at the University of Illinois at Urbana-Champaign in high energy physics, I started teaching the second semester of physics classes at Amundsen High School in the Chicago Public Schools. I did not know what to expect, as any first-year teacher knows, but now, almost exactly 20 years later, I have had an incredible ride and cannot imagine working in any other job. I have been at Evanston Township High School for 16.5 years, and now reflecting on why and what I love about teaching, I wanted to share 49 reasons - that number, 49, is in honor of the 49 colleagues from around the world who are finalists for the first Global Teacher Prize! I am not sure why I am mentioned in the same breath as this amazing group of teachers and human beings, but I am thrilled and humbled to have been selected.

Here goes: Why did I go into teaching, and why do I love working with high school students?
1. To inspire;
2. To motivate;
3. To encourage;
4. To make students think and wonder about the world around us;
5. To help students grow intellectually, socially and personally;
6. To think creatively about problems;
7. To help students become better problem solvers;
8. To help them build confidence and self-esteem;
9. To (hopefully) be a positive role model;
10. To mentor;
11. To show the role of STEM in everyday life;
12. To listen;
13. To share an enthusiasm for learning;
14. To teach physics at whatever level students can handle;
15. To show how science is connected to politics, history and economics.
16. To learn from colleagues;
17. To coach;
18. To advise on student research;
19. To collaborate with colleagues in ETHS and at Northwestern University;
20. To help students prepare for the next level - college and/or career;
21. To help guide and prepare the next generation of teachers;
22. To promote teaching as an essential profession for all of society;
23. To help create educated, scientifically literate citizens and voters;
24. To show how science is necessary to solve numerous national and global problems;
25. To do science with students;
26. To share ideas with colleagues, either through professional development training or publications;
27. To share resources with students around the world (e.g. the class blog and how to videos online);
28. To relate science to other core classes all students take;
29. To form strong relationships with students so I know what works for them as individuals;
30. To brag about students in many hundreds of letters of recommendation for college and jobs;
31. To help develop the next generation of science education tools and pedagogy;
32. To discuss STEM related careers;
33. To provide guidance to college science programs;
34. To improve students' technical writing and communication skills;
35. To create and share countless, bad science puns! I live for moans and groans after a bad pun!
36. To meet with parents to help them with their children's futures;
37. To have daily laughs and giggles with all the crazy situations students get into;
38. To provide opportunities outside of the classroom for students to pursue personal interests;
39. To work on the achievement gaps between different groups of students, such as in Project Excite;
40. To create a safe environment for all of us to fail, and then learn with each other from those failures;
41. To create and use a wide variety of lessons, to reach every individual student;
42. To create a growth, capable of anything mindset for each student;
43. To help each student realize their strengths and weaknesses and interests, and then improve;
44. To allow the freedom to try new things and promote creativity;
45. To allow students to share with each other;
46. To share experiences as a scientist;
47. To be passionate about learning, and compassionate towards all;
48. To have one and only one rule: The Golden Rule (except for the cell phone rule: if a phone goes off  
      during class, that person must dance on a lab bench for the class! Students made this one up!)
49. To never give up on any student, and to not allow them to give up on themselves!

Here is to teachers everywhere - Thank you for all you do! And to the other GTP Finalists, thank you for a shot of teaching adrenaline because of the AMAZING things you are doing - your biographies can only inspire me and any other teacher on the planet!!!

Thursday, January 29, 2015

Details on Air Friction

Thanks to Nathan H. for finding this site.

There is a useful NASA site that gets into air friction a little deeper than we do in class. This link takes you to a description of the drag coefficient (like the constant we use) - see some of the details and other factors that go into the drag term, which leads directly to an understanding of how strong air friction will be on an object. Have fun with it!

Sunday, January 25, 2015

Time Dilation equations for Gravity (from General Relativity)

Thanks to Dan M and Colby for finding the Wikipedia link for gravitational time dilation.

We have mentioned in class that Einstein, from his general theory of relativity (which is our modern theory of gravity), figured out that gravity should affect time. Two clocks that start off synchronized should 'run' at different rates in different gravitational fields. This can be deduced from the principle of equivalence, which states that the effects of acceleration are indistinguishable to the effects of gravity. Acceleration is a change in motion, and Einstein showed how motion (i.e. speed) slows time in his special theory of relativity, so accelerating motions should also slow time. If acceleration affects time, then gravity must, too! This is all verified through experiments using atomic clocks.

We can get some sense of how big (or actually, how tiny!) these gravitational effects are for a few different situations.
- As a function of height above the earth, we can use an approximation:
          T = 1 + gh/c^2     This tells us how much time dilation there would be if one clock was on the ground and one was at a height h. This assumes h is very small compared to the size of the earth (or whatever object we are using for g). Because c^2 is very large, 9 x 10^16, you can see that this is a tiny effect for the earth! So the difference between the times being kept by the two clocks is in that term gh/c^2.

- Above a spherical, non-rotating object
       t_surface = (t_far)*sqrt [1 - 2GM/(rc^2)]
This tells us the difference in two clocks, one on the surface of a spherical object and one far away from the object. M is the mass of the object and r is the distance from the center of the object, which is not rotating. Note that the term 2GM/c^2 is the Schwartzshild radius, which is the radius one would need to crush the object to make it a black hole (escape velocity > c).

- A special case of being above a spherical object is if you are in circular orbit around that object. The above expression becomes
       t_surface = (t_satellite)*sqrt[1 - 3GM/(rc^2)]

In any case, this is very cool stuff! Have fun just by playing around with these expressions and discovering how large or small the effect would be for any scenario/object you wish!
Note I have videos on equivalence principle, warped space-time (from Elegant Universe), basics of general relativity, Gauss's law for 1/r^2, Gauss's law inside Earth, gravitational potential energy, and integration to find g-fields for rings and sticks. There is also videos for E = mc^2, and Einstein's energy equation and consequences.

Tuesday, January 20, 2015

Links to Final Exam Solutions

For 3 Chem-Phys (periods 1-2, 8-9), click here for solutions to the semester I final exam.

For AP Physics C (periods 3-4), click here for solutions to the semester I final exam.

Go over your answers/solutions, and do an error analysis and/or make corrections on your exam. Be sure things make as much sense as possible, and save any remaining questions for me or a classmate who might have an understanding of it.

Sunday, January 18, 2015

Buoyancy - When do submerged objects rise or sink?

Buoyancy is a neat force, which is that upward push a fluid places on an object. Swimming would be a bit difficult if buoyancy was not there, since then everything and everyone would just sink!

Archimedes figured out long ago that the buoyant force = the weight of the displaced fluid. This video gives a brief example and proof to something that you may be aware of, that whether things sink or float depends on the relative densities. In chemistry, oil floats on water if it is less dense than water - well, here is the 'proof' of this phenomenon using Newton's 2nd law. I hope it helps!

Center of mass of systems: Position and Velocity

The center of mass is a really useful concept. It can be used to reduce a large object, say a planet or star, to a single point that has the entire mass of the object at that location. This is the key concept for calculating the gravitational force between the objects, for example.

But this is also a useful concept for system of objects or particles. We can define the center of mass for a system with a weighted average of
           x_cm = [sum of (individual mass)(individual x-coordinate)] / (total mass of system)

We have used this to find the center of mass of a binary system, which is then the center of each object's orbit. But for even more numerous particles, the center of mass of a system describes the motion of the entire system, even if all the particles are flying around seemingly at random. This video presents two simple 1-D collision problems to show how the momentum of the center of mass of a system is conserved, and moves at a constant velocity (assuming no external forces acting on the system that would cause the center of mass to accelerate).

Wednesday, January 7, 2015

Review for Finals

OK, 'tis the season for final exams!

For the juniors, the review sets are sets I, II, and III, which can be found here. The solutions are also on this page, as well as the Princeton Review sets and solutions. You can also check out any old AP problems here, as well as all the grading solutions/rubrics. There is a file in the AP Exams folder that shows which years have problems on different topics, so you can find practice problems quickly.

All the videos can be found on a class blog page.

Don't forget that there are numerous worked examples and odd problems you can try on any topic in the textbook, as well as in the electronic version you should have access to at Mastering Physics.

As always, I recommend study groups - can you explain definitions, concepts, problem solutions, etc. to others so they understand? It is a terrific way of learning and reviewing and helping each other.

We have optional review on Monday, and the test will be on Tuesday. Let's get it done!!