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Wednesday, December 7, 2016

Relativity and Energy: How E = mc^2 leads to numerous other features of Nature!

In my classes, when we are going through the usual classical physics portions of energy and work, I also thrown in a couple days of modern theories of energy, including special relativity and some basic quantum mechanical ideas. After we see one way of deriving E = mc^2, and Einstein's energy equation in special relativity, I want to make a point that this is a truly large breakthrough in our thinking of the physical world. I like to use E = mc^2 as a stepping stone to better understand the following:
The discovery of E = mc2 basically sets up the discovery of quantum  mechanics, and the weirdness we see with particles.
            Energy = matter, is effectively what this tells us.

These are two forms of the same stuff, like steam (energy) and ice (matter)  are two forms of the same H2O molecule.

=> Whatever properties energy (waves) can have, then matter (particles)  has those properties.
     Whatever properties matter (particles) can have, then energy (waves)  has those properties.

Examples:
If waves have wavelengths, then so must particles
If particles have momentum, then so must waves (light/photons)
If matter is affected by gravity, then so must waves (light/photons)

This equation also re-defines conservation of mass and conservation of energy. In nuclear reactions, conservation of mass is violated, since products weigh less than reactants.
         Conservation of mass-energy is now more correct!

  • This equation changed the course of history, as we entered the age of nuclear power and weapons.
  • It allows us to understand how stars form and 'burn,' and their life cycles
  • It allows us to understand how heavier elements are formed through thermonuclear fusion (nucleosynthesis; we are made of star dust!!)
  • It allows us to understand how the universe can form from a burst of pure energy (Big Bang), as we have phase transitions from energy to matter or vice versa.
  • The unification of space and time allows us to understand what causes gravity (warps in space-time)
  • It allows us to understand how to make particle accelerators and explore the basic question, "What are we made of?"
  • It led to the prediction of antimatter 
  • It allows us to think in terms of multiple dimensions, giving rise to things like string theories
  • It allows us to begin to understand radioactive processes, and nuclear physics
  • The theory of photons allowed Einstein to understand photoelectricity (solar energy), for which he won the Nobel Prize
  • This also helped lead to his discovery of 'stimulated emission,' the process that makes lasers possible

  • It predicts 'matter waves' or the wave-particle duality, which is the heart and soul of quantum mechanics

Wednesday, November 16, 2016

Resistor Circuit Analysis

Check out the video about how to analyze resistor circuits, with both series and parallel sets in the same circuit. Take notes on this, and try the first three examples in the packet. Then you and your lab partners can work on completing the two labs. Also, check out a video on multi-loop circuits, and also a video on band theory (focus on how and why the bands form in the first place), which may help with your conceptual understanding in here as well as in chemistry.

Thursday, November 10, 2016

Juniors - Consider Summer Science Program (SSP)

For Juniors: One of the very best and intense summer programs is the Summer Science program.  This is a chance to get into some upper-level physics and astrophysics, learn some coding, and get into projects of tracking and simulating asteroid orbits, and more! We have had a few get into this program and they loved it, including one current senior who is willing to chat about it to anyone who's interested. Check it out and apply!

Monday, November 7, 2016

CT-STEM site and assessments for 3 Chem-Phys

Go to the NU CT-STEM site http://ct-stem.northwestern.edu/ and log in. This is from that email you should have received a week or two ago. CT-STEM stands for Computational Thinking in STEM, and we are participating in this program as new curricula are being developed and piloted for widespread use in the next few years, as much of the country has adopted the Next Generation Science Standards. You should have two assigned tasks, one a survey and one a pre-program assessment. These are just done online, and should not take a huge amount of time. Your scores will be used as part of a larger study at NU about the effectiveness of the activities we will do throughout the year, and your names are anonymous in the study. Thanks!

Monday, October 31, 2016

Classes on Halloween

Periods 1-2, 8-9

The students should break into groups of 3-4 and try the 8 circular motion questions, and get it turned in. Once this is completed, watch and take detailed notes on videos for the two types of air friction cases we do. The first is when air friction is the only force acting on an object, like a hockey puck. The second is when there is a second force acting on an object with air friction, such as on a skydiver. Note that something that comes into play for teh skydiver type problem is the chain rule. Check out a video for chain rule if this is a new concept for you.

Students should then be sure to have the pendulum mini-lab completed and shared with Doc V at vondracekm@eths202.org. We will go through the priorities Tuesday.



Period 3

Students will get there tests back with solutions. They should review and make corrections together, in small groups of 3 or 4. They should talk through and make sure everyone in the group is OK with each answer/solution.

Then, students should watch and take notes on two videos. One is an introduction to circular motion, and the idea that a force is needed to allow a car to make a turn. And then a second that introduces the concept of centripetal force - a force pointing inwards, towards the center of the circle the object is moving around. We will start to make sense of this tomorrow, using pendulums.

Sunday, October 30, 2016

Article on Hunting for Planet 9 - a large 'Ghost planet' - using laws of gravity in simulations

There is a Scientific American article on the hunt for planet 9, that presumed planet way the heck out there is a 10,000 year-plus orbit. It is presumed because of computer simulations that suggest there must be something out there to account for the motions of other objects within the solar system. And these simulations are based on the laws of gravity, which we are studying right now to understand at least the basics of orbits. Scientists have narrowed where to look for the planet by half, so the hope is to have visual contact in the next few years to confirm what the simulations predict. By the way, it is predicted to be about 20 times the mass of the earth, and have an orbital radius that averages between 380 and 980 AU (1 AU is the radius of earth's orbit, or 93 million miles). If you are participating in the research club, then the programming skills you are acquiring could be used to do such simulations in the future! All of this stuff fits together at some point!  :-)