Doppler Effect: Frequency, Pitch and Volume.

If you are not entirely sure of how pitch and the Doppler effect are related, this one is for you.

The Doppler effect describes how the pitch heard from moving sources of sound such as planes, trains or automobiles varies (predictably) depending on whether the source is approaching, or receding. Or - is it the volume that changes? When a source of sound comes closer, surely it also gets louder and its volume also changes.

It is not usually pointed out in descriptions of the Doppler effect, but it is a fact that when a source of sound approaches or recedes, both the volume of sound as well as its pitch, change. If you  are not sure what is what, you may confuse one with the other, and end up not fully appreciating Herr Doppler's simple yet brilliant insight.

Let us back up a little. When an object is struck with some force, the energy behind the force is transmitted to the object in a few different ways. For example, it is manifested as mechanical vibrations and as heat. Right now, we're interested in the vibrations. A surface that is vibrating and is in contact with a medium such as air (or water, or anything that is not a vacuum), also makes the medium vibrate at approximately the same rate. These vibrations - layers of air being compressed and released in synch with the vibrating surface, like an accordion - travel outward and are heard as "sound" when they reach our eardrums.

The number of times per second the surface vibrates (and by extension the air around it), is called the frequency. Frequency is an objective physical quantity that can be measured independently by one or more instruments, and can be validated across readings.

However, frequency is perceived by human ears as pitch, which is a subjective quantity. In other words, pitch depends on the observer and is not the same for all observers. Pitch is the inner human sensation that is produced in response to the frequency sound, so there are many factors that go into it. Doppler's effect is about the perception of sound by human beings, so it is about pitch. When a sound source is travelling towards you, each successive vibration that reaches your ears travels a shorter distance, and this has the effect of making the pitch rise.

A rising pitch is what you hear when the guitarist slides from the nut (where the tuning keys are located), towards the bridge. You hear a decreasing pitch when he slides in the opposite direction. Spend some time listening to this, and understanding how to identify a rising pitch and a falling pitch. In this example the volume remains the same, so you can also practice separating those two concepts out.

The next time you hear an approaching ambulance or plane, realize that its volume is rising but so is its pitch, and focus on that rising note to understand what the Doppler effect describes. Sound sources that are receding register a lowering pitch. A fascinating extension of the Doppler effect is found in electromagnetic waves; light sources that are travelling at speeds comparable to that of light, register similar shifts at the ends of the spectrum of color, and allow astronomers to calculate their velocity.

Chemical reactions: blow hot, blow cold

Life seems to thrive on the fact that warm and cold are, well..., two different temperature ranges! It is November now, and the northern hemisphere heads into winter just as the southern hemisphere starts heating up to start up their summers.

This magical arrangement is caused by the Earth's tilt, the same feature that creates the weather (winds, rain, storms, clouds, precipitation), and the seasons, and many things that are interesting about the Earth's surface.

As if to mirror this property of Nature, every known chemical reaction is either endothermic  (requiring, or drawing in heat) or exothermic (giving off heat). An easy way to remember which is which, is to remember that "endo" is Latin for within and sounds like "indo" - heat is pulled in. Exo is Latin for outside, so it describes reactions that give off heat, sending heat outside. Simply put, an exothermic reaction gives off heat and feels warm.

When two or more chemicals react, it is really their molecules that come up against each other and react. Some molecules have high valencies (available, unpaired electrons) and so react easily at room temperature, usually releasing heat energy when the chemical bonds are broken. Other molecules need to be heated to reach a level of energy at which old chemical bonds can be broken to form new ones. The former are exothermic, and the latter are endothermic. Chemical reactions that occur in nature tend not to be thought of as "chemical reactions" because there is no laboratory in sight, but they are valid chemical reactions all the same - the formation of ammonia in a lightning storm, the rusting of iron, the fermentation of barley and hops to form beer, and so on.

Rusting iron gives off heat, whereas the fermentation in baking bread requires heat. Making ice cubes gives off heat (surprising? But unless a body of water lost more heat than it absorbed, it could not get colder, and turn to ice) whereas melting ice absorbs heat and so is endothermic.

Can you think of other commonly seen reactions, and classify them as endothermic or exothermic?

iPad apps for Physics: A great Thanksgiving gift idea!

The Exploriments blog wishes all its readers a Very Happy Thanksgiving!

Greetings to those who celebrate Thanksgiving by enjoying the long weekend with friends and family and the science geeks who'd rather curl up with a good science blog or video - spare us a few moments now, and you'll thank us later when "Back to School" madness begins.

We have made Physics fun for middle and high school students by bringing our apps to the Apple Store and iTunes. Our interactive learning objects continue to be available online at, but now they're also at your fingertips, on your favorite device the Apple iPad. We at Exploriments know the benefits of simulation-based learning, and we would love to get the good word out to everyone in the community.

If you are a 1:1 iPad school, a committed parent or a passionate teacher, Exploriments will be your best friend. As of this writing, there are Exploriments for iPad available in the areas of Motion, Fluids, Electrostatics, Electricity, Force and Light - all using interactive touch-based simulations, with illuminating content as well as recommended explorations. 

View Exploriments on iPad now and bookmark the link too - we update the tabs as we build and release new apps. Try the free Weight and Mass app to get a taste of simulation-based learning - it is fun and easy to understand. Happy Exploring! 

Sandy and Nilam. Those depressing visitors!

Hurricane Sandy began receding on October 31 2012 from the Eastern seaboard of the United States, and cyclone Nilam hit the Eastern seaboard of India on November 1 2012. Both are examples of naturally recurring phenomena that create havoc and cause losses worth billions of dollars, and hundreds of lives every year. The affected areas are still limping back to normalcy.

Cyclones ("hurricanes" in North America and "typhoons" in Japan) are giant storms that have high winds and heavy rainfall produced by a circling vortex of clouds that can be over a thousand miles across. Cyclones are caused by weather depressions. But they are also the cause of fiscal and mental depression because of the damage and chaos they cause.

You can better understand low pressure or depression by understanding pressure itself. 

The Earth is wrapped in a 75-mile-thick film of air; to scale, that is like the film of water on a wet basketball. Towering over any point on the Earth's surface is a column of air approximately 75 miles high. This column of air, with help from the Earth's gravitational pull, exerts a force. Force measured per unit area is called "pressure", and the air we breathe exerts a measurable atmospheric pressure on everything around us, at all times. 

The air is not equally dense at all altitudes - 75% of the air is available closest to the Earth, a zone going all around that is less than 11 miles high. This is the air made up mainly of Nitrogen and Oxygen that all creatures breathe. As you go higher, the density of air reduces as there are fewer and fewer molecules of air available, and it gets more and more difficult to breathe. On the surface of the Earth, this pressure - commonly known as atmospheric pressure and measuring 1 bar or 101,315 Pascals - is equivalent to a standing column of 76 cm of Mercury. In other words, the pressure exerted by 75 miles of atmospheric air equals the pressure exerted by 76 cm of the much denser fluid, Mercury.

An atmospheric depression, therefore, is a low pressure zone within the Earth's atmosphere. It is caused because differing sunshine from the tropics to the poles causes differing ocean temperatures and air temperatures, which in turn causes low and high pressure regions. The characteristic of a low pressure region is that air from surrounding areas rushes in to equalize the pressure. Put very simply, air rushing in to fill an atomospheric depression is what produces high winds, that sometimes go on to create a hurricane; the spinning, moving vortex is formed because the zone of depression itself keeps moving due to the rotation of the Earth.
The greater the difference in ocean temperature, the greater the depression, the greater the velocity of winds, and the greater the storms that are produced. Ever since the invention of barometers, it has been noticed that a drop in air pressure could mean the onset of a storm. Climate change in recent decades has meant higher and higher temperatures, which produce deeper depressions and bigger, more destructive storms.

Keep in mind that 1 bar, or 1000 millibar, is the normal atmospheric pressure at sea level. The atmospheric pressure at landfall of hurricane Sandy (940 millibar) was lower than the pressure of cyclone Nilam (990 millibar). The apparently small difference in pressure, however creates a much magnified effect at the scale of a storm - Sandy had winds as high as 110 mph compared to the 50 mph winds of cyclone Nilam. You can track global temperatures, see how they affect barometric pressures, and understand how depressions form and produce storm systems.

Fearless Felix's free fall, and a discussion of terminal velocity.

14 October 2012: In a much-televised event Felix Baumgartner jumped off a pod floating 39 km (24 miles, or 128,000 feet) over the Earth's surface and straight into the history books.

In one fell swoop, he set the record for the highest jump and the highest speed ever achieved by a non-powered human being in air - 1.24 Mach. Yes, quite astoundingly, he reached a speed of 1,342 kilometers per hour (834 mph), which is 1.24 times faster than the speed of sound. Despite his preparation and the modern technology available to him, an earlier jump by his mentor Joseph Kittinger remains the record for the longest free fall (4 minutes, 36 seconds!)

Felix Baumgartner at work:

Kittinger's free fall record, set way back in 1960,  reached a speed of 988 kilometers per hour (614 mph). While Kittinger's is truly remarkable for being an outrageously bold pioneering attempt, Baumgartner's is special for breaking the sound barrier.

A force "F" that moves a body of mass "m" through a fluid, does so with a resultant acceleration "a", since F = ma. Acceleration causes velocity to steadily increase. Since any real fluid is not without resistance, movement happens at the cost of the body overcoming the fluid's resistance. Eventually, there is a point at which the motive force equals fluid resistance. At this point, the resultant force on the body is zero, which means its acceleration goes to zero, and it cannot go faster than the velocity it has achieved, the so-called "terminal velocity". Any body freely falling through the Earth's atmosphere accelerates at the rate of 9.8 m/s, gradually increases its speed until air resistance nullifies the acceleration.

These achievements, entirely credit-worthy though they are, can create a small doubt in the minds of science aficionados in the matter of terminal velocity: How did these gentlemen manage to exceed the terminal velocity, which is known to be 195 kilometers per hour (122 mph or 54 m/s)?

The answer, my friend is blowing in the wind; terminal velocity is a function of air resistance, and that presupposes the existence of air. Most of the air molecules in the Earth's atmosphere exist below an altitude of 5.5 km. The altitude from which this jump was executed is seriously lacking in air molecules, and therefore lacking in air resistance. Without air resistance, there is theoretically no upper limit to the velocity achievable by a body under acceleration, and that is how Felix Baumgartner was easily able to surpass the terminal velocity as well as the sound barrier.

Assuming that for most of the fall Felix Baumgartner encountered only negligible air resistance, the distance he would have fallen to reach the speed of sound (with initial velocity u = 0, final velocity v = 340 m/s and acceleration = 9.8 m/s):

d = (v2 - u2)/2g = 3402/2x9.8 = 115600/2x9.8 = 5898 m or 5.8 km

Also, distance in terms of time taken "t" and acceleration "g", where initial velocity is zero, is:
d = gt2/2

Therefore, the time taken to reach this velocity would have been:
t = sqrt(2d/g) = sqrt(2 x 5898/9.8) = 34.69 seconds.

Comparing the zero-air-resistance calculations to the facts of his free fall (39 km in about 260 seconds), you get an idea of what a great deterrent air resistance is - even when much reduced.

Sports Science: The Unpredictable Knuckleball

What do all sports have in common? Activities as diverse as baseball, basketball, cricket, swimming, gymnastics, snooker/billiards, carrom (or carroms) and cycling all involve an application of one or more principles of science. Sports, with its preoccupation with balance, trajectory, speed, timing and spin, is nothing but a living and breathing science laboratory.

What better way of starting a sports segment on the Exploriments blog than with the national US pastime - baseball? Baseball is so fascinating because it is a duel between the batter's skills and the pitcher's skills. While pitchers frequently employ the fastball, it is the knuckleball that is a more interesting Physics study.

The main skill in throwing a knuckleball, other than being able to dig your fingernails in to hold the ball, is to not impart any spin to it. A good knuckleball turns only a few times during its entire flight. The fact that it has no spin leaves it susceptible to wind eddies and the vortices that form over its seam, and this makes it float in unpredictable ways. 

A regular fastball spins fast about its own axis, giving it the angular momentum and rotational inertia which helps it resist changes to its position. This gyroscopic effect helps the ball retain its orientation and course, making it more predictable to follow around and to catch or hit. A knuckleball neither has the spin, nor the gyroscopic effect associated with spin, making the trajectory of the ball difficult to pick out. This video from Reuters TV shows this Physics principle in action:

The Best iPad apps for STEM and Science Education

Exploriments on iPad are a marriage made in iTunes heaven. They are a boon for all STEM (Science, Technology, Engineering, Mathematics) initiatives and a way to kindle an interest in learning.

Why Exploriments?
Exploriments are apps that use a visual, simulation-based model that invites interaction in the form of touching, tapping and flicking. This game-like feel creates involvement and hikes the fun factor.

Why Visual Simulation?
A computer application (or, Apple app) is more engaging when it is interactive, dynamic, and intuitive. As human beings with opposable thumbs and articulate fingers, we have all evolved standard gestures from interacting with the analog (or real) world. Here are some gestures we use to communicate or realize intention in the real world:
  • Jab or point fingers to indicate something
  • Turn pages by flicking or swiping
  • Move objects on a smooth surface by tapping to grab, dragging and releasing.
  • Stretch a flexible surface to increase its size, by parting our fingers
  • Roll a cylinder, or show traffic flow by "scrolling" our fingers 
The Language of iPad
Anyone who has used an iPad and has been impressed with its ability to understand what you want it to do, can map each of the gestures mentioned above to an iPad gesture. By making the iPad support universal, non-verbal "intention gestures" on its user interface, Apple has taken our ability to convey intention to a machine to a new level. We know that the iPad is strongly identified with these types of gestures.

iPad and Exploriments - Coming Together
Simulations are computer programs that display objects which need to be moved, dropped, tilted, pulled, pushed, turned ON or turned OFF, in order to interact with other objects, or with the context (environment) itself. Exploriments provides the underlying scientific model (i.e., the rules) of how the objects are allowed to interact - however, it starts when the user first initiates an interaction, which further causes an object to change its state, position or energy level.

Exploriments help you explore Pendulums, Weight and Mass, Simple Circuits, and many more interesting concepts by using game-like simulation and interactivity. This is the ideal toolkit for making learning a fun activity.

Test drive the free Weight & Mass app listed here: Bookmark the microsite and visit regularly - we keep expanding it as we add apps.

Happy Learning!

Exploriments are ideal for 1:1 Ipad Initiative schools interested in emphasizing group learning with teacher-led demos and for injecting interactivity into science sessions - available both on the web at OR as iPad apps on the Apple iTunes Store - search by keyword "Exploriments" to see all our apps.

Exploriments on iPad: Episode III

[Previously, in "Exploriments..."

Episode I spoke about how seductive alternatives are drawing people away from education.
Episode II talked about how Simulation can be our Knight in Shining Armor.]

This episode completes the Trilogy by talking about how simulation as used by Exploriments is most effective when it joins forces with the awesomely cool iPad, and emerges as the teacher's ultimate ally in the war on science illiteracy.

An application generates more engagement when it is interactive, dynamic, and intuitive. As humans with opposable thumbs and articulate fingers, we have all evolved standard gestures from interacting with the "analog", or real world. The iPad's interface supports all these instinctive gestures, making it the ideal platform for our simulation based, game-like apps.

Visual simulations and iPads use similar languages of interaction. Add to that the Exploriments frameworks (Pendulums, Weight and Mass, Simple Circuits, etc), and what you get is the ideal toolkit for making learning a game-like, fun, and engaging activity.

Exploriments on iPad: Episode II

"Simulation based educationthe most effective e-learning strategy"

A "simulation" in the e-learning context is the scientifically correct representation of a real life experiment - such as a pendulum, a chemical reaction, the archimedes principle, friction, levers, circuits and so on. A simulation allows you to move objects around, set things in motion, use a stopwatch, connect wires, measure either voltage or a pendulum's time period, and hundreds more tasks, depending on the specific application - basically, everything you can do in a physical laboratory. 

However, a simulation can take you beyond the physical limitations imposed by a physical lab. In a simulation there are no real risks, costs, or collateral damage, and this means you can easily explore conditions that are not possible to recreate in a laboratory. For example - you can view and control satellite motion, you can change the gravity under which you observe a pendulum, you can easily change the density of a bob or the liquid when exploring Archimedes principle. You can wilfully cause short circuits, cause electrical devices to fail by passing current higher than their safety rating, or increase weight or gravitational force to the point of failure. 

Understanding science by interacting with accurately modeled virtual objects (weights, springs, measuring devices, atoms, molecules, charged particles, etc), in addition to the freedom to test  boundary conditions, are the big wins of our simulation strategy.

Simulation Differentiators:

A simulation is not a "linear" medium such as a textbook or a powerpoint presentation - that is, it does not require you to go from one thing to another, in a particular order. On the contrary, a simulation lets you approach a scenario from different starting points by varying your exploration each time, in order to get a more nuanced understanding. It promotes a more wholistic and multi-perspective understanding of concepts.

A simulation is also great for progressive learning by starting a concept with baby steps, and slowly building up to the full understanding. 

In the hands of an instructor a simulation adapts to the skill level of a student. Because simulations encompass all the relevant science, it is possible to use the same simulation either for simple, intermediate, or advanced insights.

Computer Modelled Reality being what it is, it is possible for a student or teacher to simulate a large number of combinations and scenarios - indeed, it is possible to stumble upon scientifically valid scenarios that even the creators had not thought! This is very different from a static and linear medium which presents a fixed set of problems, or highlights a finite set of explorations.

Finally, a simulation is virtual which means that it resides inside a computer's memory and can be upgraded, enhanced and improved based on both experience and feedback. Being virtual means that it can take you beyond the accepted physical boundaries of an experiment. This opens wonderful possibilities such as increasing learning potential by adding more objects or insights and increasing engagement and collaboration with a set of teachers and students.

Simulations being dynamic and game-like, do wonders for creating engagement. In the hands of a guide, it becomes an effective tool for involving students. Learning by experiencing the thrill of discovery, and by doing all the tasks leading up to it, make this the ideal educational aid in supplementing traditional methods.

Exploriments on iPad: Episode I

"Education at a crossroads"

More and more, school work is being seen as a boring, tedious, zero-fun game. 
Movies, games and networking sites are vying for students' attention (and winning). Most methods of teaching used in schools are unidirectional and non-interactive, and that does not help; classroom instruction that only uses the book-and-board route leaves many students unable to cope, or struggling with text that does not adapt to individual needs. 

Schools need a supplement to boost engagement and generate interest.

Team Exploriments believes that a human brain thrives on stimulation, and that is the secret to making learning a fun activityStudying and learning are activities that are losing ground to gaming and networking. The few students who are interested get tagged geeky or nerdy, and that scares others away. This needs to change. We need role models and change agents to drive this change.

Something is not right. Poor grades and dropouts are on the rise. The lessons taught at school will stick in students' minds if they are fun. This will contribute to a happy, successful and rewarding life. Getting students interested in our technological world should be one of the major aims of education; gaining employment and earning a livelihood are secondary outcomes that will follow automatically, if the first principle is satisfied.

While textbooks, standardized tests and classrooms have their own place, they lack the ability to engage and be fun. Students live in a seductive, media-driven world in which educational aids are forced to compete for attention.

Exploriments offers hope. These are fun apps that allow for self paced exploration

Exploriments was designed to counter this situation. Every app is built from the ground up to reflect our core belief - that a student should learn concepts and ideas the fun way - by interacting with a virtual "lab", by advancing at his or her own pace and learning progressively, by discovering concepts (ably guided by our packaged content) and letting the engagement lead the way to discovery. 

Exploriments enable a game-like immersion, and engage students through the use of interactivity.

The world of pendulums, microscopes, magnets, doorbells, CD players, MP3 players, mobile phones, microwave ovens, cars, computers or even rockets, can be the most exciting of all playgrounds. We believe that the interactivity and game-like engagement achieved by Exploriments makes it a much needed supplement for traditional classroom instruction.

Light, in slow motion!

Photography and videography are possible because everyday objects move slowly enough and reflect enough light so it can be captured by a camera. Just enough light is let in using a mechanical or electronic shutter to capture either a snapshot (in the case of still photography) or several frames (in the case of movies). So, everyday photography is all about capturing the light reflected off a surface onto a medium.

Imagine what it is to film a ray of light itself.

A photon, the particle that constitutes light, measures about 1.6 femtometers or 1.6 x 10-15 m across. This exceedingly small particle also travels exceedingly fast - at the rate of 3 x 108 m/s. Filming or photographing the movement of a ray of light would seem to be a fool's errand - and playing it back in slow motion even more so. However, a team from MIT have used a combination of innovative time slicing techniques and a monstrously fast camera to do just that. You can now watch a ray of light in slow motion, see it produce waves, and confirm its particle nature by looking around corners and inside bodies. Femto Photography is sure to bring about a revolution in imaging, please watch:

Light: Bend it like Beckham!

Celeritas. The Latin word for speed shortened to c is used to represent the speed of light. c is a part of the most famous equation in science E = mc2. The speed of light being a universal constant 3 x 108 m/s is well known, and forms the crucial base on which Einstein's theory of relativity rests.

What is often left out are the words " space". Light has the speed of 3 x 108 m/s in space, and like this post mentions, it has different speeds in different mediums. 

Eyes found in earthly creatures would not work if this were not true, and by extension, neither would human eyes; and neither would lens-based inventions such as microscopes and telescopes.

Inexplicable though it may be, light slows down when it enters a denser medium. When light travels from air into a lens, it slows down. Light then shows another interesting behavior - in what is known as
Fermat's principle of least time, it alters its path to take a route that would carry it through the lens in the least possible time; this causes rays of light to bend as soon as they enter the denser medium. The rays bend towards the nearest exit to shorten their transit time, and bend again when they exit from the lens back into air.

principle of least time, Refraction, Snell's Law, refractive index, incident angle, refracted angle
This diagram shows a red ray of light going from a rarer medium (P) to a denser medium (Q), whereupon its velocity reduces making v2 < v1. n1 and n2 are called the refractive indices of P and Q respectively. Snell's law wraps this all up in a single line:
Sinθ1/Sinθ2 = v1/v2 = n2/n1

The shape of a lens is designed to use the natural bending of light to produce effects like magnification and inversion of images that form the basis for telescopes and microscopes.

Light: A riddle wrapped in a mystery, inside an enigma

The strangest thing in the universe may also be the most commonplace.


A gift from our neighborhood star, a tonic that nourishes life on Earth, and the stuff of every rainbow. It is also a thorn in the side of Science - a constant reminder of how less we know. 
Science hangs its failures on this honest sounding word -  "paradox". The nature of light has intrigued thinkers for millennia. Scientists who have tried to win it over have succeeded only moderately - still, the romance shows no sign of waning.

There are times when light appears to be made of particles. Newton noticed that light travelled in straight lines, as if constituted from discrete particles - he called these particles "corpuscles". The famous photoelectric effect is a natural phenomenon in which light apparently knocks electrons off their orbits to create electricity - again, an indication that it is made of particles. The photoelectric effect was explained by Einstein in 1921, 
years after Newton, in a Nobel prize winning effort that proposed that light travels in quanta called photons - essentially, particles. There is more support for the particle nature of light - light travels fastest in space, where there is no intervening matter. As soon as it enters the atmosphere of the Earth, it slows down a little. When it enters water it slows down even further. 

But although light slows down when it enters a medium of higher density,
it does that only once, at the point of entry. It does not continue to slow down, as you would expect something made of particles that encounter more particles, to do. Paradox number 1. 

When light goes from water back to the air, or from air back into space - it instantly goes back to its original speed, then retains that speed forever until it enters a different medium. This sort of behaviour is a strike both for
and against the particle theory. Paradox number 2. 

Thomas Young discovered that passing light through microsopic slits produced interference patterns, much like waves in a pond. This meant that light also behaved like a wave. The "dual nature of light" is that light is a wave and a particle - 
not by turns, but simultaneously! Paradox number 3. 

If that was not bad enough, it was shown that even a single particle of light passing through a double slit can
"interfere with itself" and produce an interference pattern. That is, even though it is only one particle it can pretend to be a wave when confronted with a double slit, and produce interference. Paradox number 4.

There is currently a lot of fanfare about the Higgs Boson, aka the "God Particle". This discovery does not
yet involve any talk about light, since photons are massless and the Higgs Boson confers mass - but I would not hold my breath.  Given the history light has had with human beings, I will just say - "watch this space", to see how that story develops. We'll keep you posted.

Mercury and Mars: The Unlikely Twins

Team Exploriments has created an app for iPad that deals with Newton's Law of Universal Gravitation. It facilitates an understanding of the concepts and formulae that underlie gravitation. You can now explore gravitation the Exploriments way - by using the power of simulation.

While working on this app we noticed something interesting - to one decimal place, Mercury and Mars have the same value for acceleration due to gravity - 3.7 m/s! In a solar system with planets of wildly differing sizes, densities and masses, this is a striking coincidence. Interestingly, a recent
theory posits that Mercury and Mars were created from the leftovers of an early violent interaction between Earth and Venus. So far, there is no science that connects their g values to them being joined at the hip at birth - but feel free to air your views.

What are the implications of having the same value of "g"? 

For one thing, objects would weigh the same on both planets and would fall at the same rate.
Applying Newton's Law leads us to a more involved conclusion, as shown in this short worksheet:

mercury = G x Mmercury/(Rmercury)2 = gmars = Mmars/(Rmars)2 = 3.7

mercury/(Rmercury)2 = Mmars/(Rmars)2

The M/R
2 ratio of both the planets is the same. You can do the exercise of plugging in the known values of Mars and Mercury to verify this simple, yet interesting fact that makes these two planets unlikely twins. Are you aware of other surprising coincidences linking Mars and Mercury, or other gravitation factoids that you would like to share?

Foucault Pendulum: Getting into the swing

We wrote before about how Galileo's insight into the isochronism of pendulum motion occurred at Pisa in 1581 AD. Then, as though keeping time with a cosmic pendulum, Léon Foucault unveiled his discovery in the year 1851 - an anagram of the number 1581 !

By 1851, it was long known and accepted that the Earth rotated around its own axis, and that this movement  created the illusion of "sunrise" and "sunset". Rotation produced 12 hours of daylight for a stationary observer on the surface of the Earth facing the Sun, and 12 hours of darkness facing away from the Sun. However there was no terrestrial proof, or any satisfactory visual representation of the fact that the Earth rotated.

Although Foucault made several important contributions to the science of Optics, he is best remembered for the innovative use of a Pendulum to demonstrate the rotation of the Earth - to anyone willing to wait and watch for at least an hour. To track the Earth's rotation, a pendulum would need to remain in motion for a couple of hours at least, and do so undisturbed by air currents or breeze. He needed to create a long and heavy pendulum, and he needed to create it indoors. He chose the Pantheon in Paris as the site of his demonstration, because it had one of the highest indoor suspension points available in Paris - the apex of its dome. The weight of the pendulum would help it overcome air resistance, and its length would give it a large period and swing, making it easy to observe.

He suspended a heavy bob from a 67 m long wire suspended from the roof of the Pantheon's dome and carefully set the pendulum into motion. It was important to set the pendulum into motion without imparting even a hint of sideways motion or spin, because that would dilute the validity of the observation.

The shiny golden sphere is the pendulum bob of the Foucault pendulum at the Pantheon

Markers on the ground allowed observers to note the points between which the pendulum moved in a straight line. Amazingly, even after a comparatively short span of 30 minutes, everyone could see that the pendulum's line of movement had shifted away from the initial marker points. The pendulum now swung between two points that were a few degrees clockwise of the original two points. After several hours, it was even more obvious that the pendulum seemed to be drifting more and more in a clockwise manner - and over a period of 32.7 hours, it would sweep the 360 degrees of a circle. At the poles, this duration would be approximately 24 hours, in keeping with our conception of the length of a day.

The Foucault pendulum works because the plane of the pendulum's movement does not respond to the Earth's rotation. As the Earth rotates in an anti-clockwise direction in the above perspective, the pendulum simply remains in its own plane, not following the Earth's rotation as viewed from a distant celestial object. 
Experiments also established that the Foucault pendulum "precesses", or "drifts" and loses time at different rates, depending on the latitude. This was mainly because of the difference in the Coriolis force component that changes gradually from the Equator to the Poles.

This video gives us an idea of how slowly a 67 m long pendulum swings. Note the markers set up below the pendulum, which allow you to track how the Earth rotates, while the pendulum continues to swing in its own plane relative to the stars.

Science by staring at the ceiling

"Don't stare at the ceiling!" is a common admonition teachers use with students staring vacantly into space. That is because nothing says "daydreaming" like a student staring at a ceiling. It brings out the worst in teachers, and rightly so. And while we're all for paying attention in class, sometimes a little off-hours daydreaming can be a good thing.

It can be a good thing for Science, that is. Idle thoughts can produce lateral insights, which in turn become scientific breakthroughs, discoveries or inventions. Seeing the commonplace with fresh eyes is an Art - but it is an Art that spawns Science.

When something is new, it excites our senses and holds our attention; this changes when it becomes  familiar. Ever notice how the excitement of taking a window seat dwindles after the route becomes familiar? Or the excitement of seeing a rainbow, or the falling snow, or a sunset?

When the mind is the disease, absent-mindedness is the cure! The laws of Nature are hidden because familiarity prevents us from seeing them. Here's how a great Science discovery resulted from a certain somebody staring at a ceiling:-
A view of the Cathedral's ceiling
The year is approximately 1582 CE. Imagine Galileo seated on a pew inside the Pisa Cathedral. Bored, distracted, maybe even daydreaming, he stares at the gently swinging chandeliers suspended from the ceiling. As the energy of the swing slowly fades, the lamp swings in smaller and smaller arcs, finally coming to rest. In a gradually accumulating lateral insight, he notices something quite unexpected - the swings, from the longest to the shortest, all take the same time! This is contrary to what he expects (indeed, contrary even to modern intuition) - that longer swings should take longer, since a greater distance is being traversed.
We are not sure just how he verified this discovery. Maybe he first used his own pulse, then realized that the interval between any two beats was not uniform; or maybe, the excitement of discovery caused his pulse to race, so he abandoned the approach. Maybe he used a musician-friend's acute sense of timing to measure the duration of chandelier swings - we don't know for sure.

What we do know is that Galileo discovered the single most important (and surprising) aspect of suspended masses - their isochronism or "same time"-ness. He discovered that a pendulum's time period is independent of the width of swing, or the weight of the suspended object. This meant that the time of oscillation for a pendulum would remain the same until it stopped, and this caused a revolution in time-keeping. Further experimentation helped Galileo derive this formula for the period T:

T = 2(pi) x Square Root(L/g)

Scientists who came later built on this knowledge and created devices based on the use of a pendulum, and the pendulum slowly became the time keeping heart of our civilization. Foucault noticed an even more interesting aspect of pendulums, but that is a different story...

Got iPad? Try our Pendulum app:

To weight or not to weight, that is the question!

Although the confusion over weight and mass is an old issue, it still has the potential to confuse students that are new to science.

In the simplest terms - the stuff or matter that makes up an object is its mass. Unless an object is scuffed, worn down, or is radioactive, its mass does not change. 
On account of having mass, (stuff, matter) objects are tugged at by gravity. The resultant force felt by a body is called its weight. The Earth has mass, so everything else with mass is attracted by the Earth.

The weight of a body therefore depends on the gravitation of its environment - a body that is in the weaker gravitational field of the Moon weighs less. Similarly, it weighs more on Jupiter.

What actually causes confusion in science is this; the units of mass, the Kilogram (kg) and the pound (lb.) are used 
conventionally as units of weight. A statement such as  "I bought 10 kg of groceries" is fine for everyday conversation. What it means in scientific terms is this - "I bought groceries with a mass that exerted a force of 98.1 Newtons (or 10 Kg x 9.81 m/s^2) force on the weighing scale". You can see why the short form was adopted for conventional use.

Our assumption that the force of gravity (9.81 m/s^2) is the same everywhere on Earth, lets us measure weight but pretend that it is mass - this being a "no harm, no foul" situation because the error is equal for everyone on Earth. 
In other words, units of mass are used for a property of mass that translates to its weight.

: A two-armed pan balance neutralizes the force of gravity by letting it act on both arms equally, effectively measuring the mass of an object. On the other hand a single-pan balance, or a spring balance, effectively measures the weight of the object. A two-pan balance used on an alien planet would show the same reading as it does on Earth, since it is effectively measuring mass. A spring balance would show a variance depending on the acceleration due to gravity.

Quoting a mass-weight reference from the State of Florida's

Mass is the amount of matter (or "stuff") in an object. Weight, on the other hand, is the measure of force of attraction (gravitational force) between an object and Earth.

The concepts of mass and weight are complicated and potentially confusing to elementary students. Hence, the more familiar term of "weight" is recommended for use to stand for both mass and weight in grades K-5. By grades 6-8, students are expected to understand the distinction between mass and weight, and use them appropriately.

Our convention of using mass units for weight works as long as everything is measured on Earth. In a future where interplanetary travel is common, the two pan balance may become the only acceptable way of measuring consumables for commerce. A can of paint bought from the Walmart in Iowa can only be sold to the base near Cydonia, Mars if mass is being measured, and not weight.

A kg on Mars is the same as a kg on Earth.

To experience these insights, try our free Mass & Weight app for iPad:

Conventional Current Vs Electron Flow: swimming against the tide?

The idea that electricity flows from the positive terminal to the negative goes all the way back to one of America's Founding Fathers, Benjamin Franklin. In Ben Franklin's time, there were no batteries, and no knowledge of the existence of electrons. He discovered that when certain hard, smooth substances were rubbed against cloth-like fibrous surfaces, an attractive force was created between the two.

If the bodies were brought close to each other, the attractive force would discharge between them as a spark. Franklin imagined that a special kind of fluid called "electric fluid" existed in the bodies, and would move from one body to another when they were rubbed together.

In order to record his experiments for posterity he needed to give names to the new ideas and objects he was dealing with. He imagined that the hard and shiny things - glass, wax, amber and sulfur - had more electric fluid than the materials with fibers on the surface - wool, dry cloth, or fur. He concluded that the electric fluid moved from a place of plenty (he called it "positive") to a place of deficit ("negative"). After Ben Franklin wrote about this idea in 1750, everyone adopted it because he was a respected pioneer in the field.

People continued applying Franklin's convention about electricity flowing from positive to negative even after batteries were invented, because there was no reason to challenge that view.

J.J. Thomson discovered electrons in 1897 to great fanfare. Right after that, it became obvious that rather than positively charged particles going from positive to negative, the reverse was true! It was the negatively charged electrons moving from negative to positive, that we experienced as "electricity". By 1897 however, Franklin's convention had been in use for nearly 150 years, so appeared in thousands of books, tens of thousands of electrical circuit diagrams, and millions of minds by then.

Although Franklin's convention is not true in the context of conducting metals, it continues to be used in textbooks and circuits showing conducting metals (i.e., wires). Interestingly however, there are some cases of electric flow in which his convention holds true! When electricity flows through conducting fluids (electrolytes), positively charged particles (ions) flow from positive to negative, thereby matching the direction of conventional flow as imagined by Ben Franklin. There are a few other cases where the conventional direction is actually matched by the flow of postively charged particles.

As a concession to tradition, we refer to the direction of current that Franklin imagined as "conventional flow". Scientists are now in agreement that in metals,  electrons flow from negative to positive and produce electricity (nothing actually flows from positive to negative).

Does pressure produce science?

Isn't pressure part of Physics, which is a part of Science? How then can pressure produce Science?

However, we're talking about psychological pressure - as in a challenge, a deadline or a threat - and not physical pressure. Mental pressure varies - learning environments differ from country to country and culture to culture. The pressure to perform academically, more intrusive in the East, is milder in the West and is overshadowed by an indulgent empowerment of students. How does this affect learning outcomes, how much pressure is right, and how to apply it without losing our humanity? These are not simple questions, but we think that debate is a good way forward.

There is a famous story of learning under pressure from antiquity. It culminates with a man so overtaken by the thrill of scientific discovery that he ran down the road, naked, shouting "Eureka!". Greek for "I Found It!".

The story begins with Hiero II, the King of Syracuse (the original Syracuse in ancient Greece, not upstate New York) commissioning a wreath of gold to be used as a holy object. Upon receiving the commissioned object, he suspected that silver was mixed in with the gold. This would make it unfit to be used as a holy artifact.

Merely weighing the wreath would not help, since it was already weighed and found to be correct. If indeed silver had been used as a mix-in, its volume would be different from a wreath made of pure gold. The King issued an order to find out, but to do so without altering, damaging or melting the artifact in any way

Now that's pressure!

A genius named Archimedes was given this job. Some day as Archimedes prepared his bath, he pondered the challenge, possibly slightly afraid of the consequences of failure. As he entered the water, it rose and overflowed as usual. But this time his heightened senses saw new meaning in this behavior. In a flash of insight, he saw that simply by measuring displaced fluid, he could find the volume of the wreath - then compare it to the volume displaced by pure gold. The result was that Archimedes found the wreath to have an impurity, did his King proud, and became a legend.

Did being in a state of stress help Archimedes formulate the famous principle of buoyancy that we know, love, and take for granted? Was it science born under pressure?

Feel free to reply with similar anecdotes - or the opposite, where people choked under pressure and produced "unscience".

What are Exploriments?

Exploriments are apps on the web and iPad for learning Science through interactions with realistic simulations.

The word “Exploriment” is a portmanteau of “Explore” and “Experiment”, and combines the sensibilities of both words. The philosophy of Exploriments is to encourage true scientific temper by creating a safety net in which experimentation can progress without fear of failure, spills, expense or mishaps.

An Exploriment is a visual, interactive environment created by a computer program. It is a personal virtual laboratory for Physics, Chemistry and Math learning.

In an Exploriment, real world interactions
produced in a virtual environment are studied for learning Science. Examples - setting a pendulum in motion and measuring its period, dropping an object through space and measuring velocity, or passing current through a device in an electric circuit and measuring voltage drop.

 An Exploriment helps you learn by performing tasks - that makes it more engaging and immersive than watching videos or slideshows. Watch a video demonstration of an iPad Exploriment on Fluids and Buoyancy:


Just as sportspersons use shadow practice to sharpen their responses and fighter pilots use flight simulators, Exploriments use simulation to take you past a laboratory, to the center of the Earth, to distant planets like Jupiter, and even to the surface of the Sun in order to further your understanding of Science.

Exploriments are available either as web applications on or as iPad apps on the App Store at iTunes. Welcome to Simulation-based learning. Welcome to Exploriments. Join the revolution!