Measure the Speed of Light using a Chocolate Bar

Step 1. check the Shopping List:

This is a very short shopping list for a super-cool activity that is used in college-level physics labs!

• A large 1 lb. bar of chocolate (I use Hershey's, but any kind should do)
• A ruler, pencil and paper
• A microwave oven and a plate

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Step 2. Do the activity yourself:

Measure the Speed of Light using a Chocolate Bar

When you warm up leftovers, have you ever wondered why the microwave heats the food and not the plate? (Well, some plates, anyway.) It has to do with the way microwave ovens work.
Microwave ovens use dielectric heating (or high frequency heating) to heat your food. Basically, the microwave oven shoots light beams that are tuned to excite the water molecule. Foods that contain water will step up a notch in energy levels as heat. (The microwave radiation can also excite other polarized molecules in addition to the water molecule, which is why some plates also get hot.)

One of the biggest challenges with measuring the speed of light is light travels really fast… too fast to watch with our eyeballs.  So instead, we're going to watch the effects of microwave light and base our measurements on the effects the light has on different kinds of food.  What's really cool about this experiment that you can see the size of the wave for yourself by measuring the burn marks in the chocolate. Microwaves use light with a wavelength of 0.01 to 10 cm (that's the size of the wave itself).

Key Concepts

Energy can take one of two forms: matter and light (called electromagnetic radiation). Matter is what stuff is made from, like a chair or a table, and we'll talk a lot more about matter when we get to chemistry.
Light is energy that can travel through space and through some kinds of matter, like glass. Another word for light is “electromagnetic radiation”. Light can have high energy, lower energy, or anything in between… kind of like high energy kids (the ones who race all over the playground), lower energy kids (the ones reading a book in a corner), and kids whose energy is somewhere in the middle.
Scientists usually refer to the light energy you can see with your eyes as “visible light”, or just “light”, and it has middle-of-the-road amounts of energy – not high, not low. Just average. That kind of electromagnetic radiation is called “light”.

Lower energy electromagnetic radiation can have wavelengths longer than a football field, and those are called “radio waves”. These aren't the kind of waves that a guitar string makes when you pluck it. Radio waves are not sound waves. They are waves made out of electricity and magnetism (which we'll discuss later) that travel through space. Sound waves need something, like air, in order to travel because it does it by vibrating molecules. Electromagnetic waves work differently, but it's a little more complicated than we're going to discuss now, so just remember that light waves are different than sound waves. If you've ever seen a lightning storm, you know this is true, because you see the lightning way before you hear the thunder. Which wave do you think travels faster? Light or sound? Other examples of lower energy waves are the kind found in your microwave oven called “microwaves” (surprised?) Your TV remote uses infra-red electromagnetic radiation, which has a little more energy than microwaves. What about high energy waves? If you've ever been curious about why the dentist puts a heavy lead apron on you before x-raying your teeth, it's because they're about to use high-energy electromagnetic radiation called “x-rays” to see through your mouth tissues to get to the bones and teeth. Since high-energy rays can destroy living tissue, you have to wear that apron. Lead stops most high-energy electromagnetic radiation in the x-ray range. Black holes, supernovae, and quasars in the deep reaches of space emit deadly x-rays and even higher-energy gamma rays.

Experiment 

Video  http://www.superchargedscience.com/lnc813-16.htm

Materials:

• chocolate bar (extra-large bars work best)
• microwave
• plate
• ruler
• calculator
• pencil and paper

 

1. First, you'll need to find the ‘hot spots' in your microwave. 
2. Remove the turntable from your microwave and place a naked bar of chocolate on a plate inside the microwave. 
3. Make sure the chocolate bar is the BIG size – you'll need at least 7 inches of chocolate for this to work.
4. Turn the microwave on and wait a few minutes until you see small parts of the chocolate bar start to bubble up, and then quickly open the door (it will start to smoke if you leave it in too long). 
5. Look carefully at the chocolate bar without touching the surface… you are looking for TWO hotspots, not just one – they will look like small volcano eruptions on the surface of the bar.  If you don't have two, grab a fresh plate (you can reuse the chocolate bar) and try again, changing the location of the place inside the microwave. 
6. You're looking for the place where the microwave light hits the chocolate bar in two spots so you can measure the distance between the spots. Those places are the places where the microwave light wave hits the chocolate.
7. Open up the door or look on the back of your microwave for the technical specifications.  You're looking for a frequency in the 2,000-3,000 MHz range, usually about 2450 MHz. 
8. Write this number down on a sheet of paper – this tells you the microwave radiation frequency that the oven produces, and will be used for calculating the speed of light. (Be sure to run your experiment a few times before taking actual data, to be sure you've got everything running smoothly.  Have someone snap a photo of you getting ready to test, just for fun!)

Going further: You can experiment with other easy-to-melt foods, like cheese, buttered bread, chocolate chips, peanut butter, or marshmallows! Just pop in the first food type on a plate (without the turntable!) into the best spot in the microwave, and turn it on.  Remove when both hotspots form, and being careful not to touch the surface of the food, measure the center-to-center distance using your ruler in centimeters.
TIP: If you're using mini-marshmallows or chocolate chips (or other smaller foods), you'll need to spread them out in an even layer on your plate so you don't miss a spot that could be your hotspot!

How to Calculate the Speed of Light from your Data

Note that when you measure the distance between the hotspots, you are only measuring the peak-to-peak distance of the wave, which means you're only measuring half of the wave.  We'll multiply this number by two to get the actual length of the wave (wavelength).  If you're using centimeters, you'll also need to convert those to meters by dividing by 100.
So, if you measure 6.2 cm between your hotspots, and you want to calculate the speed of light and compare to the published value which is in meters per second, here's what you do:

2,450 MHz is really 2,450,000,000 Hz or 2,450,000,000 cycles per 1 second

Find the length of the wave (in cm):

2 * 6.2 cm = (12.4 cm) /(100 cm/m) = 0.124 meters

Multiply the wavelength by the microwave oven frequency:

0.124 m * 2,450,000,000 Hz = 303,800,000 m/s

The real (published) value for light speed is 299,792,458 m/s = 186,000 miles/second = 671,000,000 mph. How did you do?

Questions to Ask

1. What would happen if you used cheese instead of chocolate?
   
2. Does it matter where in the microwave the chocolate is located? Does placement of the chocolate affect the wavelength?
   
3. Can you explain what the burn marks on the chocolate bar are from?
   

A Recorded Online Physics Class

PHYSICS CLASS

https://sas.elluminate.com/site/external/jwsdetect/playback.jnlp?psid=2011-02-16.0945.M.A5BB78333AC4FEC568A60D2CE9B0FA.vcr&sid=voffice

Physics of the Stone Arches (NOVA interactive)

Arches

Medieval architects were masters at building with stone. But as cathedral design evolved, some medieval architects began to push beyond the boundaries of known structural design and into unknown territory.

With the pursuit of taller and taller cathedrals, any errors could lead to catastrophic collapses. In this interactive, try your hand (safely) at constructing a cathedral arch and learn more about the physics behind the arch.

Launch Interactive

  See if you can build a cathedral arch without it collapsing, and learn more about the forces at work.

Editor's Note: The arch diagrams and thrust lines are simplified for illustrative purposes. Our interactive arch exists in a virtual world that does not completely reflect real-world physics.

Levers (hammer, ruler & thin rope)

You are given a hammer, a ruler and some thin rope. Your task is to hang the hammer from a table. The thin rope is not long enough to tie the hammer to the table.

And, up close . . . .

Momentum and Marbles

MOMENTUM

Inertia means that a rolling ball on a smooth, level surface will roll forever if nothing stops it.

In fact, friction and air pushing against the moving ball will eventually bring it to a stop.

But interesting things happen when a motionless object gets in the way of a moving one. Try this and see for yourself.

1. Tape the yardsticks to a tabletop so they're parallel and about 1/2 inch apart.
2. Put 2 marbles in the middle of the sticks (our 'track') a few inches apart.
3. Flick a marble so that it rolls and hits the other one. 

Notice that the one that had been rolling stops while the one that had been still now rolls!
The momentum of the rolling marble transfers to the other one, stopping the first and setting the second in motion.

1. Now put two marbles on the track so they touch, and a third several inches away. 
2. Flick the single marble into the other two. 

Notice that the rolling marble stops, the middle one stays put, and the third one rolls. The momentum went through the second marble into the third.

Try other combinations: two marbles into three still marbles, or three into three. You'll find that however many marbles you set in motion, the same number will be made to roll when they're hit.

This experiment introduces 3 concepts about and momentum :

• Momentum can transfer from one object to another.

• Momentum can pass from one object, through a second, and into a third.

• The total amount of momentum at the beginning will stay the same.

EXPERIMENT SUPPLIES
Supplies: Yardstick, Marble

Science Jim's Chat with a Physicist #3

If you have ever wanted to find out more about astrophysics or dark matter then today is your lucky day.   Check out this Science Jim's Chat With a Physicist recording! (about 60 mins) Click to the website and then click the pic to start the recording! The recording is just like watching the live class so feel free to re-size the video window, move the windows around, or whatever you want!

Science Jim's Chat with a Physicist #3 

Slam Dunk Science

VIDEO HERE

Basketball players looking to rule the court may need more than just skill and endurance to be a top player. A good dribble, some fancy footwork ... It might look good on the court, but when it comes to playing the game, getting the ball through the hoop is what basketball is all about. But it'’s not that easy for every player. Now, physicist and former college ball player, John Fontanella, teaches a few basic principles of science to help players make the basket every time!

Basketball players looking to rule the court may need more than just skill and endurance to be a top player. A good dribble, some fancy footwork ... It might look good on the court, but when it comes to playing the game, getting the ball through the hoop is what basketball is all about.

But it'’s not that easy for every player. Now, physicist and former college ball player, John Fontanella, teaches a few basic principles of science to help players make the basket every time!

One popular move is the jump shot. But many players release the ball too soon and miss the basket.
“"One of the most important things that I found is that the ball really needs to be released right at the top of the jump,"” Fontanella said.
At that moment, the player isn't moving -- his velocity is zero. Releasing the ball at the top gives the player better control of the ball and making it more likely that he will make the shot. Another shot, the lay-up, can be an easy shot to make by hitting the backboard at just the right spot.
“"I found the sweet spot for a right-hand lay-up and the sweet spot for a left-hand lay-up,”" Fontanella said.
The secret is hitting the top corners of the square on the backboard; the angle of the ball is perfect and lands the shot almost every time.
“"A little bit of knowledge of physics helps you play the game better,”" Fontanella said.
The American Association of Physics Teachers contributed to the information contained in the TV portion of this report.

BACKGROUND: Good basketball players develop their skills through endless repetition, hard-wiring the brain with the correct sequence of muscle movements for optimal play (“kinesthetic memory”). However, knowing a little basic physics can still help you improve your game. You can learn why you should put a spin on the ball, get tips on improving your free throws, and discover the secret to Michael Jordan'’s seemingly longer “hang time.”

PUTTING A SPIN ON IT: Once the basketball leaves the shooter’'s hand, it travels in an unchanging parabolic path that can be calculated using Newton’'s laws of motion. But putting a backspin on the ball can help you make more free throws. When a spinning ball bounces, it bounces back in the direction of the spin. If the ball hits the backboard or back of the rim, it will be directed toward into the basket. That’'s because when the ball makes contact with the rim or backboard, the backspin causes a change in velocity opposite to the spin direction, making it more likely that the ball will drop into the net softly.

HANG TIME: Michael Jordan earned the nickname “Air Jordan” because of his seemingly longer “hang time” making jump shots in games, but this is an illusion. How high someone can jump depends on the force used to push on the floor when starting to jump, which in turn depends on the strength and power of the jumper’s leg muscles. The harder and more powerful the jump, the higher and longer the flight. In order to leap four feet into the air, the hang time would be 1.0 seconds. Jordan had a few tricks up his sleeve to make that hang time seem longer. When he dunked, he held onto the ball a bit longer than most players, and actually placed it in the basket on the way down. He also pulled his legs up as the jump progressed so it appeared that he was jumping higher. But it still all happened in less than one second.

Cross Posted @ Homeschooling Notebook (March 7, 2011)
Source: Science Daily.com
original article date: November 1, 2007

Non Newtonian Fluid

Note: I really HATE all the advertisements here but the info is good.

(fluid mechanics) A fluid whose flow behavior departs from that of a Newtonian fluid, so that the rate of shear is not proportional to the corresponding stress. Also known as non-Newtonian system.

Learn How to create a non-Newtonian fluid. For more Science How-To Videos & Articles, visit WonderHowTo.

CAVEAT! 
1) I have no control over the lettering superimposed over this video.
2) Let me be clear ~~~> I do NOT recommend any other videos by this young man. -- I include this one only because it is harmless and it demonstrates a simple science experiment that introduces non-Newtonian properties that are easily experienced. AGAIN, I do NOT recommend any of his other videos.

THESE I DO RECOMMEND:
•  Mythbusters Season 4 Disc 1 
• AND!!  Learn about the nature of fluids 

FLUIDS IN GENERAL!

Kitchens are full of fluids you might never have known were there. A fluid can be a liquid, gas, solid, or even plasma. 

Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress. In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. Put simply, the less viscous the fluid is, the greater its ease of movement (fluidity).^[1]
Viscosity describes a fluid's internal resistance to flow and may be thought of as a measure of fluid friction. For example, high-viscosity felsic magma will create a tall, steep stratovolcano, because it cannot flow far before it cools, while low-viscosity mafic lava will create a wide, shallow-sloped shield volcano. All real fluids (except superfluids) have some resistance to stress and therefore are viscous, but a fluid which has no resistance to shear stress is known as an ideal fluid or inviscid fluid.
The study of flowing matter is known as rheology, which includes viscosity and related concepts.




Cross posted @ http://homeschoolingnotebook.blogspot.com/2011/01/non-newtonian-fluid.html



SOURCES:
http://dsc.discovery.com/videos/time-warp-non-newtonian-fluid.html
http://www.answers.com/topic/non-newtonian-fluid
http://video.answers.com/learn-about-the-nature-of-fluids-83227076
http://www.youtube.com/watch?v=i_2u0fV3qTM&feature=channel