A Matter Of Time

Gravity must certainly have been among the first natural forces that mankind became aware of at the dawn of history. Throughout the centuries gravity has remained the most constant and omnipresent of all forces men had to grapple with in their everyday world.

Even an early man knew that if he let go an object held in his hand it would fall to the ground. However millenniums would have passed before anyone seriously thought of how an object would fall under the force of gravity. Even the 'common sense' that heavy objects fell to the ground faster than lighter ones, a belief reinforced by the great Aristotle of the ancient Greece would have to wait for another more than a millennium before being disposed by another great man by the name of Galileo Galilea.

Nobody really knows if Galileo actually dropped any object from the famous tower of Pisa (presently The Leaning Tower of Pisa in Italy) in his quest for the understanding of gravity. What is more important is the legacy left behind by this great man hailed as the first serious experimenter of science. Accurate experiments during Galileo's time were of course very difficult with limited and yet crude apparatus. The clocks then were even far less accurate than the ones in our ordinary home. What more, in the absence of vacuum facility, free fall experiments were simply impossible. Despite such handicaps, Galileo predicted correctly that objects, irrespective of size and shape, would fall with constant acceleration in the absence of air resistance -- a prediction proven true experimentally years later by Robert Boyle with the help of a vacuum pump invented by him.

Today, we have the privilege of using modern scientific equipments to actually observe what took Galileo much difficulty to predict. Stroboscopic photographs have clearly shown the constant acceleration of free falling objects irrespective of size and weight. Photography can be considered as one of the greatest inventions of mankind. Photographs have enabled events to be captured for further observations not possible with naked eyes. High speed stroboscopic still photographs and motion pictures have opened a new floodgate of investigations and brought about knowledge previously too fast to be observed.

Multi flash high speed and movie cameras allow activities occur in milli or even micro seconds to be observed and understood by students of introductory level science. Multi flash or strobe flashing at an interval of hundredth of a second has enabled many images of a free falling object be taken. (The time required by an object to fall freely a height of 1 metre is about 0.45 seconds only.) As a further extension of the discussion, we know that a cat usually lands on its feet irrespective of how it falls. Under normal circumstances, we will probably be able to observe only the initial and final stage of a falling cat. However, how does a cat move and turn its body in order to land gracefully and proudly (especially if it is released from your grasp at an upside down position) with such a short time interval, only special high speed photograph will reveal its skill. Similar photographic technique has enabled detailed photograph showing sequences of movement by a tennis player when serving a ball can help tennis coaches as well as manufacturers of tennis racquet to acquire crucial information for specific uses. Now-a-day, high speed motion photography is commonly used to enable more detailed viewing. This is evident from frequent 'slow motion' display or replay of a soccer player sending a high speed ball into the goal and that of a speeding Formula 1 car crashing into a barrier.

With the advent of even more advanced technology, high speed movie cameras can even shoot up to 500,000 frames per second. Such high speed capability has enabled details of the detonation of grenade be seen for the first time. Graceful glide and spin of a bullet emerging from the muzzle of a gun can be seen as clearly as seeing an old steam locomotive crawling out of a tunnel.

Recent advances in high speed laser technology have resulted in high speed photography acquiring a new meaning. Compared with the latest breakthrough, the time intervals discussed in the early part of this article can be considered as snail-paced. Science has taken a new turn in 1987 at Caltech of California. A new word 'femtochemistry' was coined to describe a brand new area of chemical physics, that was, in large measure the work of Professor Dr Ahmed Zewail and his colleagues. Using the most advanced laser techniques, he and his team have been able to obtain greater insights about the precise nature of chemical bonds. For the first time the precise moment of bond-breaking, bond-formation, as well as the transition stage in between, during a chemical reaction, have been successfully recorded using laser of time sensitivity of 'shutter speed' of a millionth of a billionth of a second or a femtosecond. Such high 'shutter speed' is required to capture the bond changing event which lasted for only a trillionth of a second! With this remarkable breakthrough, another new floodgate of science has been opened promising even greater height of scientific advancement, in particular, in molecular dynamics that will certainly find multiple applications in chemistry, biology and physics. One just needs to surf the Internet to get a glimpse of the vast number of related researches. It is beyond my capability to discuss meaningfully the work of Dr. Ahmed Zewail that led to the formation of femtochemistry and his subsequent award of the Nobel Prize in Chemistry in 1999. However, I would strongly recommend those who are interested to start off with his inspiring autobiography 'Voyage Through Time -- Walks of Life to the Nobel Prize'.

Compared with the days of Galileo Galilea where observations have to depend solely on the unaided eyes, mankind have progressed by leaps and bounds in the techniques of observing events that take place in very short duration of time. The quest for high speed photography will not end here as long as there is an insatiable thirst for new knowledge for more events of even shorter duration. Will the quantum limitations impede further progress?

References

Ahmed H. Zewail. Voyage Through Time, Walks of Life to the Nobel Prize. World Scientific Publishing Co. Pte., 2002.

Alan E. Nourse, M.D. Universe, Earth, And Atom. Harper & Row, Publishers, 1969.

Jerry D. Wilson, Anthony J. Buffa. College Physics Forth Edition. Prentice Hall, 2000.

Jim Jardine. Nat Phil 'O' Text. Heinemann Education Books, 1974.

M.V. Detheridge, M. Nelkon. Introductory Physics, Book One. Chatto & Windus Educational, 1974.