Report from the Festival

This past Saturday I went to Expo Day for the San Diego Science Festival. There was a big turn out for the event at Petco Park. Science organizations set up booths to share information through activities and demos, mostly geared towards kids.

I like the idea of the festival: represent science in San Diego and involve the public for free.

Most of the booths had very simple activities for the kids. That didn't stop me and my friend from participating, though (c'mon, the flier says the festival is for kids ages 3 – 93). We poked sticks through balloons without popping them, made DNA necklaces, looked at amphibians and reptiles, and solved a math problem for good measure.

The booths made a complete loop around the stadium. Because there were so many booths and people, you could only spend a short time at each one. While the festival promises to “excite your mind”, the crowds and the short activities didn't provide enough oomph to "excite my mind". Even if you gear it towards kids, you can still make something intellectually engaging for adults, too. But there was some exciting eye candy, like robots, can launchers, and plasma tubes.

Some people were great at explaining their demo to you, and others were...not so great. At science museums I always see the bicycle wheel gyroscope demo. A person stands on a turning platform and holds an upright, spinning bicycle wheel. When she tilts the wheel to the right, she and the platform turn to the right (and vice versa to the left). I had never actually done it, so I hopped on the platform and took the wheel. A couple middle school students were in charge of the demo, so I asked one of the girls why I can use the wheel to turn myself. She knew that it had something to do with spinning the wheel, but she admitted she didn't know what happens when you tilt the wheel. (What happens: conservation of angular momentum. When you tilt the wheel, you change the direction of its angular momentum. The wheel correspondingly exerts a force on you and you begin to turn in the direction that conserves angular momentum.)

If there's anything to be improved: maybe they could offer free workshops to provide something more in depth. Also, the booths were poorly organized. If they were organized by category (i.e. physics and astronomy, the environment, health, biotech...), it would be much easier to pinpoint what interests you and go there. The booths were scattered all over the place, but if they were also physically organized by category, you could find what interests you and hit up the booths that way.

That said, there was great representation and turn out. Just having all of these organizations readily available is a good start. I had a good time. This year my friend and I just volunteered at the information booth, but next year it would be fun to be at one of the actual booths interacting with everyone.

Numb3rs

Did you know that 31 million plastic bottles can be produced from 17 million barrels of oil?

Really. You don't believe me? What's that, you did the math?

Ok, you got me, I lied. If what I said was true, that would be one barrel of oil to make 2 plastic bottles. Pretty absurd, right? Actually, one barrel of oil makes 2,000 plastic bottles. That sounds better, doesn't it? What I meant to say was that 31 billion plastic bottles can be produced from 17 million barrels of oil.

That was a mistake published in the LA Times. And according to another LA Times article, "the million-billion mistake is among the most common in journalism." The article goes on to lament that the collective numeric literacy rate in America is "appallingly low".

I agree that most people do not have a good feel for numbers. Take simple quantitative estimations: how many feet is one block? How many liters of water fill up your bath tub? How tall is the tree in front of your house? In basic physics classes they try to teach you to get a feel for orders of magnitude and size. The problem is that up until taking those physics classes, I perhaps got most of my experience back in the second grade when I guessed how many jelly beans were in a jar.

There are some great visualizations of numeric quantities that I've come across. On his blog Jay Epperhart posted a cool visualization of what ONE BILLION means. And he uses the universe, with all the galaxies containing their stars and planets, to do it. Not only did I get a reference point for the number one billion, but I also got a small peek at how insignificantly small and humble Earth is. Also, xkcd has a great guide to visualizing numbers with the metric system

It's a pity that we aren't very numerically literate, because math uses numbers all the time. We're literate in English, of course, but not in the universal language that is math.

"I am convinced that the act of thinking logically cannot possibly be natural to the human mind," writes astrophysicist Neil de Grasse Tyson in his book The Sky Is Not the Limit. As math is based on the rules of logic, it is reassuring to know that for the vast majority of people, it doesn't come naturally. Like most other endeavors, it takes effort and practice to begin to appreciate the underlying beauty.

The stigma attached to math is that it is tedious and impenetrable. In his book Tyson mentions a publisher who commented that when writing a book about science, every equation included in the book will decrease the potential buyers by one half. And yes, equations are intimidating. Why make the effort if they are foreign to you?

But what if the education in America prepared us to appreciate the beauty of math, i.e. to be numerically literate? We were forced to read __________(insert tedious and boring book required for high school English) to better appreciate the English language, but we didn't get the same rigor and results to be well-versed in the language of numbers.

SD Science Festival 2010

This Saturday is Expo Day for the SD Science Festival, and I think I'm going to volunteer. I've never been to it before but it looks like fun:

The San Diego Science Festival is back! Widely known as the largest celebration of science on the West Coast, on March 20-27 the Festival is hosting dozens of countywide events promising to “excite the minds” of thousands of students and their families. As a grand finale, there will be 150+ hands on activities and stage shows at Expo Day at PETCO Park on Saturday, March 27. Check out the online calendar for complete details: http://www.sdsciencefestival.com/

How to see in 3D

I was sitting in the theater last week ready to watch my first 3D movie in the theaters, Alice in Wonderland. I looked down at my 3D glasses thinking, “Whatever happened to those red and blue glasses?” The kind you could find in a box of Captain Crunch? The glasses I was about to put on looked like geeky sunglasses. How did they work, anyway?

You might be familiar with the basics of making 3D images. It starts with how humans perceive depth.

Binocular vision

We have two eyes spaced about 5 centimeters apart to view the world at two slightly different angles. The brain processes these two perspectives and merges them into one. The brain also compares the two perspectives to calculate depth. Close your left eye and look at this WORD. Then close your right eye and look at it. The position of that word is different depending on which eye you open. The greater the difference in position, the closer the object is to you.

Stereographs

If you've played with stereographs you know how 3D images work. There are two side-by-side images, each taken from a slightly different perspective. You view the images through some kind of big goggly glasses so that your left eye only sees the left image and your right eye only sees the right image. Ta-da, the image jumps out at you!

3D Movies

Binocular vision is the idea behind filming a 3D movie. Essentially, two cameras film the same scene from slightly different angles (the two cameras are like our two eyes). 

Two projectors are used to simultaenously project the film from the two camera angles onto the screen. That's why the screen looks fuzzy when you try to watch the movie without glasses.

Here is a simplified model. Let's say we are working with light polarized at “plus angle” and light polarized at “minus angle”. 

A polarizing filter is placed in front of each of the two movie projectors. Each filter only lets light through that is polarized at a certain angle. Here is an example of a light source placed behind a polarizing filter:

Light from the Left Camera Projector is filtered through the “minus angle” polarizer. Light from the Right Camera Projector is filtered through the “plus angle” polarizer.

The light from the projectors reflects off the silver screen, retaining its original polarization.

Then the light reaches your 3D glasses.

Your glasses have two polarized lenses that filter the light so that your right eye only receives “plus angle” light and your left eye only receives “minus angle” light.

It's a fun trick to play on your brain. The brain starts to process what you see and the objects in the movie (like Johnny Depp) appear to pop out at you!

So what about those red and blue glasses? Back in the day, they filtered by color rather than polarized light. One camera angle would use red light, and the other angle would use blue light. The red and blue tinted glasses would filter the light – same concept, different method. The problem with this method is that you can't retain good color in the 3D image.

Even More

That's the basic idea of how 3D movies in the theater work. In actuality, the polarizing filtering is more complicated. If you like thinking about this sort of thing, Wired tries to explain circular polarization and how it helps you naturally move your head around and still watch a 3D movie. There's also a link to a pretty cool visualization of circular polarization.

And if you're wondering about 3D TV – yes, you do have to buy a whole new expensive TV specially designed to show 3D images (and Samsung, Sony, and Panasonic have models on their way). 3D TV uses different technology than 3D movies in the theater.

I'm looking forward to seeing how we will adapt to all of this 3D technology and how it will change the way we tell stories.

More info:
http://www.mindspring.com/~dmerriman/Imaxwrk.htm
http://science.howstuffworks.com/3-d-glasses.htm
http://masterimage3d.com/

Physics at the Olympics

Congratulations to Yu-Na Kim, who won the Olympic gold medal in ladies' figure skating last week. I could gush on and on about Yu-Na Kim and her exquisite skating. Normal people have strengths and weaknesses, and the same goes for skaters. Some skaters have great artistry but lackluster jumps, or athletic jumping but unrefined artistry. Yu-Na Kim is very rare in that all the elements of her skating are excellent. It really isn't fair. But I love watching her.

If you were watching figure skating at the Olympics last week, you were watching physics in action! There are some very simple laws of physics at work that can make or break great skating.

Take a “scratch spin”. That's one of the first real spins that a skater learns, and the technique is very simple. Despite its simplicity, it looks very cool.



See what I mean?

So how can a skater keep spinning for so long? And if you watched the video of the scratch spin, you might have noticed that the skater actually spins faster as the spin progresses. So how is she increasing her angular velocity as time passes?

Know the answer?




It's conservation of angular momentum.

Let's call angular momentum “L”. In high school physics you learn that angular momentum is the moment of inertia (I) times the angular velocity (ω).

L = Iω

You can think of the moment of inertia as the resistance of an object to rotating about its axis. If you have a cylinder or a disk or a sphere, there is a certain resistance for that object to spin.

The moment of inertia is proportional to the mass times the square of the radius:

I = MR²

The larger the radius of an object, the larger the resistance to make it spin. Try spinning two coins of equal mass on the ground. If the second coin has a larger radius than the first coin, it will be harder to make it spin as fast as the first coin. In fact, since the moment of inertia is proportional to the square of the radius, doubling the radius would quadruple the moment of inertia.

Angular velocity (ω) is the number of revolutions per second. When a skater spins, she wants to maximize her angular velocity – she wants to spin fast!

When a skater starts a scratch spin, she spreads her arms out wide and extends them to both sides. This creates a large radius from the center of her body. She also sticks her free leg out for extra radius points.

r_a is the radius resulting from the arm, and r_l is the radius resulting from the leg. Here r_a and r_l are maximum values.

Then she slowly pulls her arms towards her chest. She also brings her free leg in towards her spinning leg. This decreases her spinning radius.

r_a and r_l are decreasing, so ω increases.

As we said, the laws of physics dictate that angular momentum is conserved. This means that “L” is a fixed value. By decreasing her radius, the skater decreases her moment of inertia (I). In order for L to remain fixed, the angular velocity (ω) must increase.

Here r_a and r_l are minimum values, so ω is large.

And that's exactly what you see when you watch a skater decrease her spinning radius (and therefore her moment of inertia). The speed of the spin increases. There is no extra pushing or external forces involved – just the skater's muscles working to pull her arms and leg inward.

So the next time you watch a skater end their performance with one of those long spin combinations – okay, he's doing a camel spin, into a sit spin, into some contorted position, into a reverse sit spin, and now oh my god he's suddenly spinning so much faster it's crazy and the crowd is on its feet...!!! You can think, “oh, well that's just conservation of angular momentum”. Sweet and simple.

Thanks to Jen Leslie for the idea to write about the science behind the Olympics! Check out her blog at Scientific (mis)Communications.

More info:
Scientific American on the physics of figure skating
http://www.bsharp.org/physics/spins