Archive for the ‘science’ Category

The Physics of Dance

Monday, September 19th, 2011

arabesque.jpgOriginating in the elaborate courts of the Italian Renaissance in the 1400s, it developed into an art form during the 17th century in France under the reign of Louis XIV. But the elegant arabesques, exhilarating grand jetés, and energetic fouettés en tournant of ballet that we know today grew out of the Romanticism of the late 1800s, when ballerinas portrayed fairy-like creatures and almost seemed capable of floating in the air.

Have you ever wondered how a dancer can seem to defy gravity while your own feet are so firmly planted on the ground? Let’s take a closer look at gravity and discover the secrets behind some of these beautiful movements.

An article about dance should make you move, right? Here’s an experiment. Stand against a wall with your heels touching the wall. Now bend over and touch your toes. Did you make it?

Why did it suddenly become so difficult to do this simple task? The problem is the location of your center of mass: the average location of all the matter in your body. When standing straight, your center of mass lies within your body just below your belly button. It is situated above your feet, so you have no trouble standing.

But your center of mass can move depending on the position of your limbs. What if your body is horizontal? In a pas de deux, a male dancer may lift a ballerina into the air. Have you ever noticed where his hands are placed? Rather than clasping her waist or her thighs, he clasps her hips. Not only do her hipbones provide support, this is the point where her body is balanced; this is the location of her center of mass. Any closer to her belly or her thighs and the balance is upset; her center of mass is no longer above him, and he won’t be able to hold her aloft.

If your body is not straight, however, your center of mass is different. Try the experiment again. What happens to your center of mass as you bend over? By moving your torso away from the wall, you move some of your mass forward. Your center of mass also moves forward to a point somewhere in front of your upper thighs, not inside your body! Continue bending forward and at some point it will have moved out beyond your toes and you risk falling over. What do you do to keep from landing face-first on the floor? Try it and see. Can you figure out why standing against the wall makes such a difference?

Dancers instinctively know that to execute a perfect turn, their center of mass needs to be over their feet. Imagine trying to execute a turn, like a pirouette, on one foot. What happens if your center of mass is not directly over your feet? You end up with a wobbly turn, or worse, falling over!

grandjete.jpgThe center of mass also helps explain those big leaps, or grands jetés, that seem to hang effortlessly in the air. After taking a few quick steps, a dancer takes a leap, one leg leading and one trailing. During the leap her head rises a certain amount. (For some numbers and more physics, check out Dr. George Gollin’s Physics of Dance website.) As soon as she starts the leap, however, she raises her legs, i.e. some mass, to be parallel to the floor, which raises her center of mass some more. During the jump, her center of mass rises more than her head, making the leap seem even higher. What is more, her center of mass moves the most at the very beginning and end of the jump; it moves very little through most of the leap, giving the impression she is hanging in the air or floating.

We are so familiar with gravity’s pull attaching us to the ground that the light airy movements in ballet take us by surprise. The movements seem much more possible, however, when we apply a little physics and see how ballet has developed to work with gravity. The result? An art form that becomes even more exquisite!

PS. Here is another experiment. Sit in a chair, with your knees at a 90° angle, your feet flat on the floor. Now stand up without moving your feet or bending forward. How did you do? Our natural instinct is to bend forward, but try it again, without bending forward! When you sit in a chair, your center of mass lies at a point above your thighs in front of your lower belly. It is impossible to stand up in the second experiment unless you move your center of mass closer to your feet, which is what happens when you bend forward.

News tidbit: Hi-res Moon photos

Thursday, September 8th, 2011

As part of the Apollo program, United States astronauts (one was also a geologist) walked on the Moon six times between 1969 and 1972, the only times humans have set foot on another celestial body. Will we ever return? As the BBC describes, NASA has released high-resolution images of the Apollo landing sites, all located on the near side of the Moon. The Lunar Reconnaissance Orbiter Camera has been orbiting the Moon since 2009 at an average altitude of 31 mi (50 km) to gain information about potential future landing sites, and was able to move into an orbit bringing it just 13 mi (21 km) above the surface. Think the astronauts left the Moon in pristine condition? The pictures reveal tire tracks, astronaut boot prints, and discarded pieces of equipment.

Share your thoughts: Would you go to the Moon if you had the chance?

Catch a Falling Star

Saturday, August 27th, 2011


Did you catch any? A couple of weeks ago, many eyes were turned on the sky to witness the annual Perseid meteor shower where, under the best conditions, viewers can see a meteor as often as every minute. Though meteor showers have been observed since antiquity, it wasn’t until the mid-1800s that they were recognized as astronomical events. But what are meteors and why the name “Perseid”? To understand, we need to step back 4.5 billion years, to the beginning of the Solar System…

It all began with a massive cloud of gas and dust collapsing under the force of gravity, flattening and spinning faster and faster as it got smaller. A star, the Sun, formed at the center and the gas and dust revolving in a disk around the star coalesced into objects of various sizes: the familiar eight (sorry!) planets, their moons, the minor planets and asteroids, and other smaller chunks of rock and/or ice.


While the largest objects are nearly spherical and move smoothly in their relatively circular orbits, comets are the unruly hooligans of the Solar System. These irregular chunks of rock and ice formed in the farthest reaches of the Solar System. Close encounters with more massive objects flung them into highly eccentric — very non-circular — orbits, carrying them extremely close to the Sun. Notice how oblong the orbit of Halley’s comet is, as well as how close it approaches the Sun. As a comet nears the Sun, heat from the Sun causes frozen gases to vaporize, releasing dust and debris in the process. The gases, which we see reflecting light from the Sun, surround the comet and stretch out in a tail due to the Sun’s radiation pressure and solar wind; the dust and debris remain behind in the comet’s orbital path.

This rocky debris left by the comet is just one source of meteoroids — called meteors when they hit the Earth’s atmosphere — but it offers the most eye-catching display for us here on Earth. If the orbit of a comet crosses Earth’s orbit, the Earth will travel through the stream of rocky debris left by the comet. Thus, the Perseid meteor shower occurs when the Earth passes through the debris trail of the comet Swift-Tuttle just as the Orionid meteor shower, occurring in late October, is due to debris from comet Halley.

And the name of a meteor shower? We have to be good observers and notice that all the meteors in a shower come from the same point in the sky, the radiant point, which lies in a region, or constellation, of the sky. So, the Perseid meteors seem to come from the constellation Perseus, and the Orionids from the constellation Orion.

When meteoroids hit the Earth’s upper atmosphere, molecules in the atmosphere and those stripped off the surface of the meteor become ionized — they lose electrons. When atoms recapture the electrons, light is emitted. Aside from a pretty show, the color of this ionization trail gives us clues to the meteor’s composition; most meteors are yellow or green, meaning they contain a lot of iron or copper.

But scientists often want to know specifics: how much iron or copper is in each meteor? Practically all meteors disintegrate before they reach the lower atmosphere, so it is a challenge to have a meteor in hand. However, some meteors do hit the ground — they are called meteorites — and, if recovered, offer us a glimpse of the very origins of the Solar System!

As the meteorite speeds through the atmosphere, its outer layers melt, but the interior remains as it was when the meteoroid formed. Most recovered meteorites contain a lot of iron and nickel, which were used by early civilizations to make tools. Far more common are stony meteorites, which look like… well… stones. Because of this, they are difficult to identify. But, if you find one, you will most likely be holding a chunk of a primitive asteroid! The asteroid probably collided with another hunk of interplanetary rock, forming a meteoroid that went hurtling through the Solar System, through the Earth’s atmosphere, and, after some years, wound up in your hand!

What’s more, that meteorite can give us some very useful information. For example, when it formed, it contained two isotopes of strontium: 86Sr and 87Sr, which has one extra neutron. Over a characteristic length of time, that extra neutron turned into a proton, creating a different element, rubidium (87Rb). If we compare the ratio 87Sr/86Sr to 87Rb/86Sr, we get 4.6×109 years. Sound familiar? Not only is this the age of the meteorite, but since meteorites are among the oldest objects in the Solar System, it also gives the age of the Solar System!

If you missed the Perseids or you simply weren’t aware of it, keep looking up. Your next chance is just a couple of months away. The Orionids occur in late October, and the Leonids show up in mid-November. Here’s to clear skies!

My experience in Davos, 2011

Monday, May 30th, 2011

I am humbled by having had the opportunity to attend the World Economic Forum in Davos this past week. During my time there, I learned that most of the interesting activity at Davos happens in the coffee lounges and hallways of the Congress Center where the interconnectivity of people causes serendipitous encounters which lead to future collaboration. The dinners and parties are great places for networking and for probing some of the most brilliant minds on topics affecting our times. Most of my friends would not agree with me, but one cannot ignore the amount of quality information being debated at the more formal lecture-type gatherings. I think most people told me they avoided a lot of the lectures and preferred talking to colleagues and new people outside the lecture halls.

The conference is perfect for people who like to learn a little out of everything since the topics of the lectures are as varied as politics of India, Climate Change, Music, Psychology, physics, and many on the current state of the world’s economy. But if what you want is a deep analysis of each of the topics, this is definitely not the place. During many of the panels, each presenter gets at most 10mins to explain their point of view and by the time everyone has exposed their opinions, the session is almost over. I quickly found that so many things compete for your attention and I for one at times felt guilty that I was missing some other interesting talk while I sat listening to a different one. A scattered, ADD-like state very akin to what we experience culturally nowadays with a multitude of platforms, friends, jobs, family, trips competing for our attention.

Nevertheless, here are some lectures that I found interesting:


Insights on China addressed the Export Policy, Real Estate, Central government policy-making and private equity of the region. The Crystal Award Cermony presented an award to Jose Carreras for his work on Leukemia awareness. He said “It is our duty to use our popularity in order to give as much back to society as we receive from it.” Celebrated music director A R Rahman received the Crystal award and Carreras sang the Passion concert for us. What a treat. The Opening address was given by Dmitry Medvedev, President of the Russian Federation, who read the peech from his iPad.


I attended a dinner talk on “Social Media Addiction” with Dan Ariely, Charlie Beckett, Trevor Doughert Reid Hoffman, Diarmuid Martin, Marissa Mayer and Clay Shirky, moderated by Loic LeMeur. Fantatstic table discussions and insights into this phenomenon by simply trying to answer the question of why is addiction to social media bad? Loic did a wonderful job at moderating the conversations.


Larry Krauss (Physics Professor at Arizona State) and Rolf-Dieter Heuer (Director of CERN) lectured on the Universe, a visual exploration of Astrophysics and Quantum physics. Moderated by Philip Campbell (Editor in Chief of Nature magazine). I liked George Soros and Christine Lagarde’s panel on an International Monetary System where they discussed lessons from previous financial crises, enhanced G20 coordination and modalities of international monetary system reform. I missed the talk by pilot/her Chesley B. Sullenberger III who spoke on Leadership under Pressure. I later heard his talk was amazing.


I would have also loved to attend the talk on Science, Discovery and Controversy with Francis Collins, Director of the NIH, Howard Alper Chair and President of Science, Technolloogy and Innovation in Canada, Dan Esty (Yale Professor) Larry Kraus and J. Craig Venter, Founder and Presidnet of the Venter Institute. But it occurred simultaneously with the social media addiction one which ended up being great.


I went to hear Bill Clinton speak, as usual charming the crowds with insights into American politics, society and the economy. I attended a lecture on Global Climate Change from a political perspective with Presidents Jacob Zuma (South Africa), Felipe Calderon (Mexico), Denmark’s Connie Hedegaard, the EU commissioner for climate action and Costa Rica’s Christiana Figueres who in my opinion was the sharpest of them all. Hedegaard said that China, once an unrepentant polluter opposed to global controls, had joined Europe in deciding to invest in clean fuel technology in order to steal a march on America in a lucrative future market.


I went to a lecture on Smart Mobility that discussed how the integration of information, telecommunication and transportation technology will change our future mobility. I escaped 15 minutes before it ended to attend Ian Bremmer’s (President of the Eurasia Group) panel on Managing “Black Swans” and “Fat Tails”. Ian did a great job but I thought the panel was too diverse focusing on too many kinds of risk such as financial, energy, environmental, political, sovereign default, etc… so the conversation did not arrive at any significant points.


My friend Itay Talgam gave one of the most fantastic talks by focusing on an analogy between orchestra conductors’ style and CEO leadership. He showed videos with examples of different styles of conducting an orchestra and its effects on the music and compared them to different business leadership situations. He was warm, funny and very engaging. Everyone in the audience laughed and even asked for more once the allotted time had finished!


Finally, one of my favorite lectures was on “The Science of Emotions” which tackled the question on “How can we master emotions for a happier, less stressful and more productive life?” Tania Singer, a neuroscientist did a superb job at explaining how there are (approximately) three parts of the brain: incentive focused, non-wanting affiliation focused and threat-focused. She talked about the correlation between different parts of the brain such as the amygdale and different emotions. She discussed experiments with sniffing natural oxytocin and how it causes people to trust and care for one another more. I can’t wait for that drug to be out in the market! The only thing is that the effect only lasts for 20 minutes. Daniel Goleman (Emotional Intelligence) talked about life-work balance and managing emotions in big corporations. There was also a female Buddhist Priest, Roshi Joan Halifax, who discussed the experiments measuring compassion and happiness in Buddhist monks.

About Eggs

Tuesday, May 17th, 2011

eggs.jpgWe eat them cooked any one of half a dozen ways in the morning.  We use them in cakes and cookies and as a meringue on lemon pies.  The particularly ambitious cook may use them in a mousse or a soufflé.  (For eggs in cooking, revisit Physics in the Kitchen.)  But have you ever stopped to think about how amazing the egg really is?

We all know that eggs should be handled carefully because their shells are incredibly thin.  Drop an egg a short distance and you have a gooey mess to clean up.  One simple tap on the edge of the counter is enough to crack open the shell.  But try this experiment: hold an egg in the palm of your hand and curl your fingers around it.  Now squeeze with all your might.

Did it break?  If you didn’t believe me and didn’t squeeze with all your strength, go back and try again.

What on Earth…?  The key to an eggshell’s strength is the fact that its whole surface is curved.  The strongest shape is a sphere, and an egg is a close approximation of this.  (The reason it’s not exactly a sphere in just a moment.)  With no corners or flat sides to weaken it, the forces you apply to the egg by curling your fingers around it are distributed equally over the egg rather than concentrating at any one point. 

This works even in the following way. Hold the top and bottom of the egg with your thumb and forefinger and squeeze.  Did it break this time?  In physics terms, we say that the egg has a high “compression strength” — you’re compressing the egg, but it doesn’t break!  In fact, an egg has such high compression strength, that (with the proper setup) it can support the weight of a small personwithout breaking.

So why aren’t eggs spherical?  The oval shape is created as the bird lays it, and this turns out to be an advantage for the hen.  The shape prevents the eggs from rolling away!  Spherical eggs would roll and roll and roll… and never return.  For birds like ostriches that nest on the ground, this isn’t an issue, and their eggs are generally more spherical.  But birds that nest on cliffs often lay very conical eggs, which roll in a tight circle around the narrow end and remain on the ledge.

What else?  How can you tell if your egg is fresh?  Eggs contain an air pocket that forms when its contents shrink as it cools after being laid.  As the egg ages, moisture evaporates and the air cell grows larger, reducing the average density of the egg.  An object floats in a liquid if it is less dense than the liquid and an object denser than the liquid sinks.  We can therefore use the egg’s density as a handy measure of the egg’s freshness!  Here’s how it works.  Place your egg in a container of water.  A fresh egg with a small air pocket will rest horizontally on the bottom.  The air pocket in a 1-week-old egg is slightly larger — its density is less — and the end will hover slightly off the bottom, and an egg that’s 2-3 weeks old — even less dense — will rest vertically on the bottom.  Don’t eat any eggs that float!

Now that you know so much about eggs, here’s a bonus question: what do eggs and Roman arches have in common? 

PS. When squeezing your egg: don’t wear any rings, and make sure your egg doesn’t have any cracks already.  My “research” egg was blessed with a crack and I ended up with a handful of broken shell and raw egg oozing between my fingers and onto the floor!