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!