Don’t let the movie intimidate you.  Get the facts:

Expelled Exposed:  Expelled

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Kudos to Rachel E!  Her accurate answer to why the sky isn’t violet earned her an extra-credit point.  Many of you had the misimpression that the Nitrogen in the atmosphere didn’t have a natural frequency that was close to violet but was close to blue instead.  NOT TRUE.  Violet even closer matches Nitrogen’s natural frequency and violet light is scattered even more than blue!  The reason we don’t see a violet sky is because this violet color is on the very edge of what frequencies our eyes can see.  We see blue very well, indigo not so much, and violet if we are lucky and it is VERY intense.  (Like with sound…we only hear the tones on the very edge of our range of hearing if the tones are of extreme intensity.)

For today’s blog, complete the following statement:  The coolest thing about light is…  Include in your answer an argument for your position.  Try to write an argument that would persuade all your classmates that your position is the only logical one!

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Hi guys!  See the comments to the “prism” post for some quality questions.  I found them very interesting and I bet you will too.  I really enjoyed answering them as well…so if you every have a physics-y question, bring it on, and I’ll do my best to give you an answer!

Now for today’s post: The standard explanation for the reason why the sky is blue invokes Rayleigh scattering, that the blue end of the visible spectrum of sunlight is scattered more effectively than the red end.  In fact, this Rayleigh scattering, also known as coherent scattering, is proportional to the fourth power of the light frequency, with the blues being scattered about sixteen times more intensely than the reds.  With the blues so effectively scattered into the sky by the air molecules, one sees that the sky is blue and the sun is reddened.  But violet light at the very end of the visible spectrum has a greater frequency than the blue light.  Why isn’t the sky violet instead?

By the way – the moon doesn’t have an atmosphere, so the ‘sky’ is BLACK!The Moon’s Sky

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Hi guys-

A quick post to say that the Prism post will come later this week.  Instead…talk amongst yourselves about something “Physics-y”!

Also- Note the Flickr Pics and the RSS Feed shared items along the right hand column.  You will probably find these interesting and something you can comment upon!

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Answer to Colors:  True, but with a caveat.  Most of the time the blouse looks green because the combination of colors selectively scattered to our eyes make some shade of green.  However, the caveat is that there could be no green light of the spectrum going into our eyes at all…that it is a combo of frequencies of light that our eyes combine to ‘see’ as a green color that is scattered off of the blouse.  (Remember the blue-ish light tube that, when we put our rainbow glasses on, was really a combo of many different colors of light…but not blue light at all?  The closest blue-colored light was a purple light in its emitting spectrum.)

Kudos to David S. for including in his answer the electron-configurations that determine the natural frequency of the pigment.  Extra credit also to Rachel E. for her correct, complete, consise, and well-crafted answer to the blog!

Polarized Sunglasses:  Polarized sunglasses are aligned to transmit only vertically polarized light.  The reason for this vertical orientation is that most specularly reflected light (the reflected light rays are parallel to each other) from horizontal objects will be horizontally polarized.  These sunglasses then reduce glare of reflections from water, the ground, asphalt, etc.  Suppose the right eyeglass is misaligned by about 30 degrees from the vertical.  What would you see? 

[kml_flashembed movie="http://www.youtube.com/v/ITDNTh6T5hk" width="425" height="350" wmode="transparent" /]

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Congratuations go out to Taylor, Emily E., and Wally for really thinking thru why they were seeing what they were seeing.  Extra credit also awarded to Dom for his inclusion of mirrors at right angles!  Sorry it was so difficult to see your images in the foil…it’s REALLY cool when you are able to see the image.  We’ll definitely have to ‘chip in’ for Anthony’s family to purchase quality foil….poor guy! 

What you were supposed to observe was your image flip to become right-side-up again.  However, when you wink your right eye…in the image the left eye winks back at you!  It’s too cool! 

Here is a video about the coin-bank I’ve had on the back counter of the Physics classroom and why the change ‘disappears’ when you drop it into the slot on top.  The secret….mirrors!!

[kml_flashembed movie="http://www.youtube.com/v/Mv843DgAn9Q" width="425" height="350" wmode="transparent" /]

Colors:  A green blouse looks green because green light is being selectively scattered by the blouse to our eyes.  True or false?  Explain your response. 

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aluminum foil image

 Hi guys!  Long time no see…  We’re going to try blogging again to see if it adds educational value to your Physics learning.  If you looked closely at your assignment guide you will have noticed that there will be a blog posting due every Monday and Thursday.  Like last time we were doing a lot of blogs, make sure to post by midnight!  Everyone who posts will get 2 points of credit. If I really like your post you’ll get an extra-credit point!  Happy posting.  Let’s get to it: 

 An Optical Puzzle:  A rectangular strip of metal foil is bent into the shape of an arc, parallel to the long dimension.  If you look at your reflection in the concave surface of this arc, the image will appear inverted.  Now rotate the strip slowly through 90 degrees about the line of sight so the long dimention becomes horizontal.  What do you see? 

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Reid Knabe!!! Good for you for ‘testing’ out on a scale our blog post this week!  I also particularly liked the two Andrews’ answers.  Many, many of you had some of the answer right.  Here’s the scoop:

The tiny fluctuations would be from any movement up & down since the scale truly reads normal Force.  This could happen when you raise and lower your arms AND from your circulation (if you have a scale that precise).  Also – air taken into your lungs could affect your weight also, again, if your scale can be that precise. 

As you step off the scale there is a beginning, middle, and end time frame we would see differences in your weight.

At the beginning:  You bend your knee slightly and your body moves downward which would momentarily accelerate your body downward so the scale would no longer support your full weight.  Therefore the scale reading decreases slightly.

In the middle of your step off of the scale you push downward on the scale…so the scale puts a normal Force back onto you equal to your weight + your push.  Therefore the scale would increase some.

At the end of your step, you will transfer some of your weight off of the scale onto your other foot on the floor.  This will register on the scale as a decreasing weight until you are no longer touching the scale.  This usually happens very fast unless you decide to go in slow motion! 

btw:  Some of you thought you’d weigh more if you stood on one foot instead of two.  NOT.  Your weight is your weight no matter how you choose to support it.  You’d still weigh the same even if you somehow mannaged to balance your self upside down on one finger!  What would change is pressure on that part of the scale…and we haven’t talked about pressure yet…so I’ll save this for another blog.

Get onto a scale tonight and check it out!!!

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Yesterday and today I encountered situations where parents were taking over their children’s projects.  And as a parent I know how suductive it would be to just do it instead of teaching/talking my child through what would make a good _____.  Most parents, but not all, know that thier child’s work doesn’t reflect on them as parents…but some don’t seem to ‘get it’ and do the majority of the work on the project so that it looks goooood

Caleb (my youngest) had a time-line project due today for school and he did the work with some help from me bubble-lettering the title for him and helping him find the pictures he wanted.  However, a classmate came to school with something FRAMED and wrapped in plastic to protect it from the rain! 

A collegue had a child come to her for help with a science project after school.  The child’s mother came too.  She took copious notes over what the child and my collegue were doing and kept hovering over the project…. 

As parents, we need to continually need to check ourselves to make sure we don’t fall into a trap of doing too much for our kids.  As a teacher, I know who had help and who didn’t.  I’d much rather see a B project from a student who did all the work him/herself than an A project that I know the student had help with.  Yeah, it looks good but it doesn’t help the student learn the material.

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Congratulations to Dominick who got closest to the correct answer.  Lamar was kind of on the right track too.  You all might have paid attention to Perry and Micha’s experiences with this experiment to see that it wouldn’t take a lot to raise oneself in this manner.  I liked that many of you included
Newton’s 3rd Law appropriately….good job!On another note…Blaiq didn’t score any kudos with me with his “middle name” and Wally seemed a little complementary of himself…. :)Answer to Superman:  Place a large imaginary box around the man and the chair so that only the rope extends outside this box.  (The imaginary box isolates the forces acting only inside the box from the external forces.)  The rope goes around the pulley above and supports the box twice.  By
Newton’s 2nd Law, in the vertical direction the downward pull of gravity must be exceeded by the total upward pull of the two rope segments to have a net force upward and an acceleration upward.  The tension upward in each supporting rope segment makes a total upward force 2FT, so 2FT must be greater than mg for the system to accelerate upward.  Therefore, for a 100 pound man and a 10 pound chair, the man must exert at least a 60 pound force on the rope, a feat easily accomplished.How Much do I Weigh, Anyway?:  Even if you stand very still on an accurate scale, the reading keeps oscillating around your average weight.  Why?  As you begin to step off of the scale, what do you predict for the immediate value of the scale reading?

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