The Physics of War (9 page)

Barrel of the Basilica cannon.

Basilica had a barrel twenty-seven feet long, which was longer than any cannon at that time, and it was said to be able to a project a six-hundred-pound stone over a mile. It was so large, in fact, that it took three hours to load it after each firing. But it was one of the first cannons that had enough firepower to break through a castle wall. And it wasn't the only cannon the Ottomans had. When their army lined up outside Constantinople they had sixty-eight cannons pointed at the walls. Most were considerably smaller than Basilica, but because of their number they could inflict a lot of damage.

For fifty days the Turks bombarded Constantinople with their cannons. And indeed, under the tremendous bombardment the walls began to crumble in places. They were having an effect, but the soldiers within the walls continued to repair them as quickly as they were penetrated.

Inside the city there were seven thousand defenders, while outside Mehmed had one hundred thousand to one hundred fifty thousand soldiers ready to attack once the walls were down, so the odds were strongly in his favor. But Mehmed and his men still had to get through the wall. After fifty days of bombardment Mehmed began to get impatient. Considerable damage had been done, so he sent a contingent of soldiers to see if they could break through the weakest section of the wall. The Christians fought them off, however, and many of his men were killed.

Still determined, Mehmed sent another contingent of men in a much more organized attack. They managed to actually enter the city, but again the Christians were ready for them, and, after a tremendous fight, Mehmed's surviving attackers were forced to retreat.

Finally, at about midnight on May 29, Mehmed ordered an all-out attack. Among his troops were his favorites, the highly trained Janissaries. They used everything they had as they attacked, but it seemed again that they might be overcome. Then their luck turned: someone noticed that one of the gates had been left unlocked. Some of the soldiers managed to get in and unlock some of the other gates. Mehmed's men were soon flooding into the city. Mehmed also had several ships sitting in the harbor with many more men. When they heard the news, they, too, joined the fight, and soon it was over. After fifty long, hard days, Constantinople had fallen. Mehmed claimed the city for Islam and renamed it Istanbul. Over the next few years he built numerous temples, mosques, and shrines within it.

CANNONS IN THE ENGLISH-SCOTTISH WARS

The English used their first cannon in 1327 against the Scots, and they also used it in the Hundred Years' war. The Scots first used a cannon in 1341 to defend a castle. James II of Scotland was particularly enthusiastic about cannons. He used them to attack Roxburgh Castle in 1460; it was the last Scottish castle that was held by the English, and he was determined to get it back.

In the attack he used a large cannon nicknamed “the Lion.” While he was standing beside it, however, it exploded and killed him. Nevertheless, the Scots continued the siege, and within a few days they had overcome the English and reclaimed the castle.

One of the most famous Scottish cannons was called
Mons Meg
. It was sent as a gift to James II in 1457, and is still on display at the Edinburgh castle today. It had a length of over thirteen feet and an inner diameter of twenty inches, and it fired cannonballs that weighed four hundred pounds. For some time it was the largest cannon in the world.

THE FRENCH

After their defeat to the English in 1415 at Agincourt, the French knew they had to find a defense against the English longbow. Soon after he came to power, Charles VII decided to do something about it. He vowed to expel the English from France, but he knew that a new approach would be needed. He therefore recruited the best minds in the country—particularly engineers and physicists—and put them to work. The cannon obviously had considerable promise, but there were many problems with it. At the time cannons were large, heavy, and difficult to move, and it appeared that the only way to improve their performance was to build bigger and bigger ones. Still, even the largest ones were not very efficient at breaking through castle walls. Charles set his team to work on the problems.

The best cannons at the time were bronze, but they were expensive. The team began experimenting with cast iron and various other types of iron. They also soon determined that they needed a longer barrel to allow for a greater controlled expansion of the exploding gases. They improved the cannonballs by making them slightly smaller than the cannon bore so that they fit rather tightly into the gun, but with enough room so that some of the gases escaped as a safety measure. They also tapered the barrel from the base to the mouth.

The problem of recoil had been around for years and no one knew what to do about it. At first artillerymen tried to tie down their cannons, but the force of
the recoil always broke any shackles they used. We now know, of course, that recoil is explained by Newton's third law, but the artilleryman of the day knew nothing of Newton's laws of motion. They finally discovered that the best solution was wheels: let the cannon recoil and fly backward on wheels, then pull it forward again quickly for the next shot.

Wheels also solved another problem: maneuverability. Cannons were heavy and not easy to move. Wheels solved this problem. And while they were able to do some damage to castle walls, they were not terribly effective. Only the super cannons that were incredibly heavy could do much damage. Though ignorant of the finer detail of the physics of momentum and impact, Charles's team eventually came to realize that it wasn't just the mass of the projectile that mattered. The projectile's speed as it struck the wall was also critical. The faster, the better. So they experimented with gunpowder, trying to make it more efficient, and they found that granulated gunpowder was better.

Finally, the trajectory of the projectile was a problem. At first they believed that the cannonball flew up into the air, and that at some point it dropped straight down. Although they got some insight into this problem, it wasn't solved for many years. Also, they determined that the angle at which the cannon was aimed was of critical importance. It determined where the cannonball would land. Different angles meant different ranges, so they designed the trunnion. It used ropes, wedges, and screws of various types to allow the cannon to be pointed at different angles.

Finally, Charles VII was ready, and soon he had driven the English out.

CHARLES VIII AND VICTORY OVER NAPLES

Charles VIII took advantage of the many advances made by Charles VII. In the late 1400s he assembled a huge army and decided to attack some of the cities in Italy. In 1494 the duke of Milan and others encouraged him to attack Naples. So Charles, with an army of twenty-five thousand men set out for Naples, reaching the outskirts of the city in February 1495. Between him and Naples, however, was the huge fortress of Monte San Giovanni. Everyone was sure it was impossible to get by it. It had high walls, several feet thick, and over the previous hundred years its defenses had not been overcome despite numerous tries.
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Charles wheeled his new cannons to within one hundred fifty yards of the walls and began firing fifty-pound iron balls at it. The defenders were sure they were too small to do much damage. But Charles knew better. The guns continued
to batter the walls for eight hours, and indeed, they fell. Within hours the battle was over, and Charles had lost no men. He then marched on Naples itself and took it without a battle. Charles then crowned himself King of Naples.
¹⁰

News of the siege soon spread across Italy. People throughout the land were in shock. The leaders of the Italian city-states had to act fast; they needed a defense against the new weapons. Someone soon found that if they piled dirt behind the walls, the shelling was much less effective and would do little damage.

The critical factor over the years was science, particularly physics and chemistry. But in reality, aside from war, there was little interest in science for its own sake. Astrology and alchemy were still ingrained in society. Kings had professional astrologers and alchemists in their courts, but not scientists. Mysticism still ruled.

The Dark Ages lasted until about 1500, but by the late 1400s important advances were being made, not only in military technology but also in the understanding of nature. One of the first in this era to tackle many of the basic enigmas of nature was Leonardo da Vinci, who lived from 1452 to 1519. He didn't have a significant impact on the science of his generation, however, mostly because few of his ingenious inventions were actually built, and his recordings and drawings were not published during his lifetime. Nevertheless, he is now considered to be one of the greatest geniuses who ever lived, and there's no doubt that many of his ideas were years or even centuries ahead of his time. Today he is best known to most people as a painter. Almost everyone is familiar with his two best-known paintings:
Mona Lisa
and
The Last Supper
. But he was also a master engineer, an inventor, and a scientist with an incredible curiosity about nature and a tremendously inventive imagination. He was, indeed, a genius of the highest caliber, and his studies spanned a wide range of areas, including physics, astronomy, mathematics, optics, hydrodynamics, chemistry, and anatomy.

He was born in Italy in the small town of Vinci, near Florence—the illegal son of a wealthy notary and a peasant girl. For the first five years of his life he lived with his mother, and then he went to live with his father, uncle, and grandfather. Although his father didn't have a strong influence on his intellectual life, both his uncle and his grandfather did. His uncle instilled a curiosity about nature and science, and his grandfather kept journals in which he wrote about his life and the events of the day. Leonardo picked up this habit from him and recorded his thoughts, inventions, and so on in journals he kept almost daily throughout his life.
¹

In 1466, at the age of fourteen, Leonardo was apprenticed to the renowned painter Verrocchio of Florence, one of the best artists in Italy. Leonardo learned a lot during the years he spent with Verrocchio. In 1478, at the age of twenty-six,
however, he left Verrocchio's studio, and also his father's house, and went out on his own. He was now qualified as a “master” in the guild of artists, but he found it difficult to get work as an artist. Fortunately, he had developed another talent. Over the years he made many sketches in his journals of new types of weapons. Because military engineers were in demand, he went to Milan and applied for a job with Duke Ludovico Sforza, the ruler of Milan, but Sforza, unimpressed by his futuristic and fanciful drawings of weapons, turned him down. Nevertheless, he stayed in Milan and worked there from 1482 to 1499. During this time he continued his studies of science and engineering devices, and he rapidly became a talented inventor.

In 1494 Charles VIII of France attacked Italy. When his army reached Milan in 1499, Leonardo fled to Venice, and when Venice came under attack he soon found employment as a military engineer responsible for inventing new and better methods for defending the city.

Leonardo da Vinci.

In 1502 he was employed by Cesare Borgia, again as a military engineer. Borgia put him to work making a detailed map of the area around his stronghold. Maps were new at the time, and very few maps of any sort existed. Leonardo threw himself into the job with enthusiasm, stepping off distances and so on carefully. His map impressed Borgia so much that he immediately made Leonardo his chief military engineer.

By now Leonardo had many pupils, apprentices, and followers, and in 1506 he returned to Milan with most of them. Later he moved to the Vatican in Rome.

LEONARDO AND PHYSICS

Leonardo was meticulous in taking notes. His approach to nature and science was mainly one of observation and study, but his imagination was always at work. He spent hours studying the flow of water under various conditions. He noted how it flowed around barriers of different types, and how it varied in speed as it moved. He was particularly interested in turbulent flow and the dynamics it created. And from what he learned he developed many devices that used the force of water.

He also had a fascination with the flow of air around objects, and he invented an anemometer to measure its speed. The idea of flight fascinated him throughout his life, and he spent hundreds of hours watching and studying birds as they flew. How did they manage to stay up in the air? How did they soar and maneuver so magnificently? He was determined to find out.

He did not do a lot of experimentation in the way that Galileo and Newton did, but he learned a lot by observation and study. Also, unlike other scholars of the time, he had little formal education, and he never attended university. Basically, he was self-taught. Later, however, he studied under the mathematician Luca Pacioli. Early on, many of his scientific pursuits were associated with his interest in art and painting. He studied the properties of light in considerable detail. Also, for both his painting and sculpting he needed a detailed knowledge of muscle structure and anatomy.

Although he performed no experiments, he kept detailed notes of what he observed and did. They were recorded in thirteen thousand pages that included elaborate descriptions and drawings. In particular, he left a large number of drawings of his military inventions.

Worried about infringement and the possibility that some of his military inventions would end up in the wrong hands, he used a mirror-image technique for writing in his journals. It could only be understood by reading it using a mirror. In many cases he also left out critical information or changed his diagrams slightly.

He published little during his lifetime, but most of what he left appears as if it had been set up for publication. In other words, it was in the proper form for publication.

So, how much physics did Leonardo understand? A clear scientific understanding
of most of the basic principles of physics had not yet been developed. The basic principles would be formulated later by Galileo, Newton, and others, but there's no doubt that Leonardo had an intuitive understanding of many of the basics. He certainly understood such things as force, mass, and inertia, and he knew the difference between accelerated and uniform motion. And many of his devices used wheels, hand cranks, and circular disks, so he had to understand angular speed and motion.

In particular, he made extensive use of simple machines that employed levers, wheels and axles, cogged gears, screws of various types, pulleys, and inclined planes. A machine is defined in physics as a device that makes work easier. Basically, a machine moves a force from the point where it is applied to another point where it is used. One of the simplest machines is a lever (a board with a fulcrum). In the diagram it's easy to see that we can raise a large weight with relative ease by applying a smaller force over a longer distance at the opposite end of the board.

LEONARDO'S MILITARY INVENTIONS

City-states were frequently at war with one another, and it was important that they had an edge wherever and whenever possible, so military engineers and inventors were in great demand. Furthermore, there was always the danger of invasion from other countries.

Because Leonardo was employed so frequently as a military engineer, most of his inventions were war machines. Let's look at each of them in detail.
²

Armored Tank

Leonardo proposed a design for an armored tank while he was working for Ludovico Sforza. It was a turtle-like shell that was operated by a system of gears and propelled by a crank that turned wheels. It relied on the muscle power of eight men. Guns projected out the sides in all directions, so it could have been driven into the front lines, where it would have had a devastating effect on the enemy. It was designed to be bulletproof so that the men inside would be protected from outside fire. Leonardo's diagram had a flaw, however, but there's little doubt that he added the flaw purposely.

Machine Gun

Leonardo's machine gun was not the same as our modern machine guns, which fire at a high rate through a single barrel. In Leonardo's model, eleven muskets were mounted on each of three boards in a triangular arrangement. The entire gun could be rotated so that the first layer could be fired, then left to cool. The second layer could then be fired and left to cool while the first layer was reloaded, and so on.

Leonardo's machine gun (several guns mounted beside one another).

Flying Machine

Leonardo's vision of a flying machine would eventually be used in war, but at the time he envisioned it, he didn't think of it as a weapon of war. As noted earlier, Leonardo was fascinated by the possibility of manned flight throughout most of his life, and he spent a great deal of time studying birds in flight. As a result, he eventually invented a device that he hoped would allow humans to soar through the air like birds. Its main feature was two wings that were operated by a crank. There is some evidence that he actually tested a model of it.

Parachute

Leonardo was not only interested in flying above the surface of the earth; he was also interested in floating down through the air to land safely after jumping from a great height. Although he certainly didn't understand gravity as we do today, he had an appreciation of it, and he did have a basic understanding of aerodynamics. We now know that when you jump from a great height, two forces are acting on you: the force of gravity is pulling you downward at 32 ft/sec
²
, and there is also an upward force due to the air you are falling through. As a result, your velocity does not increase indefinitely, as you might think. The upward force from the air slows you down until you finally reach what is called your “terminal velocity.” It depends on your weight, your shape, and the air pressure. For a skydiver (diver with unopened parachute), terminal velocity is approximately 120 miles per hour. If you were to hit the ground at this speed there wouldn't be much left of you. What you want is something that slows you down before you get to the ground so that you survive, and, of course, this is where the parachute comes in. Leonardo made drawings of a pyramid-shaped framework covered with cloth that was quite similar to our modern parachute, and according to tests it likely would have worked.