End of March, NOT April.
http://dc.about.com/od/specialevents/a/SmithKiteFest.htm
Date and Time
March 31, 2012, 10 a.m.-4 p.m.
Location
On the grounds of the Washington Monument, Constitution Avenue & 17th Streets, NW Washington, DC. The most convenient Metro stations are Smithsonian and Federal Triangle. For more information about getting to the festival, see Cherry Blossom Festival Transportation Guide
Tuesday, January 31, 2012
SI Units!
SI Units!
Some comments on the first class. I speak about SI units at some length. To remind you:
Mass is measured based on a kilogram (kg) standard.
Length (or displacement or position) is based on a meter (m) standard.
Time is based on a second (s) standard.
How do we get these standards?
Length - meter (m)
- originally 1 ten-millionth the distance from north pole (of Earth) to equator
- then a distance between two fine lines engraved on a platinum-iridium bar
- (1960): 1,650,763.73 wavelengths of a particular orange-red light emitted by atoms of Kr-86 in a gas discharge tube
- (1983, current standard): the length of path traveled by light during a time interval of 1/299,792,458 seconds
That is, the speed of light is 299,792,458 m/s. This is the fastest speed that exists. Why this is is quite a subtle thing. Short answer: the only things that can travel that fast aren't "things" at all, but rather massless electromagnetic radiation. Low-mass things (particles) can travel in excess of 99% the speed of light.
Long answer: See relativity.
Time - second (s)
- Originally, the time for a pendulum (1-m long) to swing from one side of path to other
- Later, a fraction of mean solar day
- (1967): the time taken by 9,192,631,770 vibrations of a specific wavelength of light emitted by a cesium-133 atom
Mass - kilogram (kg)
- originally based on the mass of a cubic decimeter of water
- standard of mass is now the platinum-iridium cylinder kept at the International Bureau of Weights and Measures near Paris
- secondary standards are based on this
- 1 u (atomic mass unit, or AMU) = 1.6605402 x 10^-27 kg
- so, the Carbon-12 atom is 12 u in mass
Volume - liter (l)
- volume occupied by a mass of 1 kg of pure water at certain conditions
- 1.000028 decimeters cubed
- ml is approximately 1 cc
Temperature - kelvin (K)
- 1/273.16 of the thermodynamic temperature of the triple point of water (1 K = 1 degree C)
- degrees C + 273.15
- 0 K = absolute zero
For further reading:
http://en.wikipedia.org/wiki/SI_units
http://en.wikipedia.org/wiki/Metric_system#History
>
In addition, we spoke about the spherocity of the Earth and how we know its size. I've written about this previously. Please see the blog entries below:
http://howdoweknowthat.blogspot.com/2009/07/how-do-we-know-that-earth-is-spherical.html
http://howdoweknowthat.blogspot.com/2009/07/so-how-big-is-earth.html
Physics - Yeah!!!
Some comments on the first class. I speak about SI units at some length. To remind you:
Mass is measured based on a kilogram (kg) standard.
Length (or displacement or position) is based on a meter (m) standard.
Time is based on a second (s) standard.
How do we get these standards?
Length - meter (m)
- originally 1 ten-millionth the distance from north pole (of Earth) to equator
- then a distance between two fine lines engraved on a platinum-iridium bar
- (1960): 1,650,763.73 wavelengths of a particular orange-red light emitted by atoms of Kr-86 in a gas discharge tube
- (1983, current standard): the length of path traveled by light during a time interval of 1/299,792,458 seconds
That is, the speed of light is 299,792,458 m/s. This is the fastest speed that exists. Why this is is quite a subtle thing. Short answer: the only things that can travel that fast aren't "things" at all, but rather massless electromagnetic radiation. Low-mass things (particles) can travel in excess of 99% the speed of light.
Long answer: See relativity.
Time - second (s)
- Originally, the time for a pendulum (1-m long) to swing from one side of path to other
- Later, a fraction of mean solar day
- (1967): the time taken by 9,192,631,770 vibrations of a specific wavelength of light emitted by a cesium-133 atom
Mass - kilogram (kg)
- originally based on the mass of a cubic decimeter of water
- standard of mass is now the platinum-iridium cylinder kept at the International Bureau of Weights and Measures near Paris
- secondary standards are based on this
- 1 u (atomic mass unit, or AMU) = 1.6605402 x 10^-27 kg
- so, the Carbon-12 atom is 12 u in mass
Volume - liter (l)
- volume occupied by a mass of 1 kg of pure water at certain conditions
- 1.000028 decimeters cubed
- ml is approximately 1 cc
Temperature - kelvin (K)
- 1/273.16 of the thermodynamic temperature of the triple point of water (1 K = 1 degree C)
- degrees C + 273.15
- 0 K = absolute zero
For further reading:
http://en.wikipedia.org/wiki/SI_units
http://en.wikipedia.org/wiki/Metric_system#History
>
In addition, we spoke about the spherocity of the Earth and how we know its size. I've written about this previously. Please see the blog entries below:
http://howdoweknowthat.blogspot.com/2009/07/how-do-we-know-that-earth-is-spherical.html
http://howdoweknowthat.blogspot.com/2009/07/so-how-big-is-earth.html
Physics - Yeah!!!
Session 1 - Physics.... YAY!
Howdy, and welcome to Physics 100!
Syllabus!
Understanding Physics
with your host, Sean Lally!
T/Th: 5:30 - 6:45, SM0326
seanplally@gmail.com
412-965-0805
Greeting physics phriends! Welcome to Physics, your new favorite class. We are here to have a look at the broad and beautiful world of physics - the science that seeks to explain the tiniest of the tiny and the hugest of the huge. Physics is a magnificent way of explaining the strangest things imaginable, as well as the most ordinary and mundane. It's a philosophical approach to physical problems - an experimentally oriented way for seeking "truth" in the universe, or at least a close model of the truth.
This semester, I will introduce you to some of Physics' greatest hits - those things in physics that (I hope) capture the imagination, explain everyday things around us, or surprise us with their inner beauty. And really, is there a better way to spend 2.5 hours a week than that? Clearly not.
Some of the ideas will be new to you. Some may seem scary - physics has a bad reputation, I fear, as a vicious unforgiving science, destroying students in its wake. Fret not, physics phriends - we are all here together to learn about our universe. Some of the ideas will be easy to you; some will be quite challenging - honestly, I wouldn't be doing my job as teacher if I didn't challenge you once in a while. Stick with me, ask questions, seek help when you need it, do homework and invest time in the class outside of the normal lecture - these are the keys to success. Above all, don't be afraid to ask questions - in class, before class, after class, by email or by a casual note left expressing something you'd like further clarification about. Got it? Awesome!
My plan is to look at ideas from the following topics: motion, gravitation (Newton, Kepler, Einstein), relativity, sound, light and optics, forces, and more. I'm open to your ideas, so don't be afraid to ask if there are topics you'd like to explore. If I can make it happen, I will.
This is a semi-large lecture hall class. The temptation will be great to skip class. Don't. You'll regret it. In the words of a student from last semester: "Really, all I had to do was attend class and pay attention. That's all it took to do well." While I can't promise you'll be as successful as this English major, I do know that frequent absences typically lead to poor grades.
Stuff:
Text - Paul Hewitt's Conceptual Physics
Tests - 3, equally-weighted and non-cumulative (other than the extent to which physics is naturally cumulative)
My course blog:
http://phys100.blogspot.com/
Also useful, especially if you aren't fond of textbooks:
http://www.physicsclassroom.com/
And just worth watching (though I didn't quite check all the facts):
http://www.youtube.com/watch?v=RmTxr7OsPj0
So, are we ready for Physics? Yeah!!!
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