Read The Physics of War Online
Authors: Barry Parker
A new military academy, the Royal Military Academy, was established in 1741. Robins applied for a position, but surprisingly, despite his impressive qualifications, he was turned down. Some people have said that this annoyed Robins so much that he became determined to show the academy what a mistake it had made, and, as a result, he threw himself into the study of the physics of guns, artillery, and projectiles.
After a careful study of the armaments of the day, he was amazed to find out how inaccurate they were. In some battles as many as 250 rounds of ammunition were fired for every enemy killed. In fact, manufacturers didn't bother to put
sights on military muskets because they were never used for individual targets. A volley of bullets fired by a large number of soldiers was the main tactic used at the time.
Robins was determined to find out what the major problems were. As a test he fixed a musket in a rigid clamp and set up targets (paper screens) at distances of fifty, one hundred, and three hundred feet. He then measured how far the bullet had strayed off the target (away from a straight line) for each of the distances. He found that at one hundred feet it was off by fifteen inches, and at three hundred feet it was off by several feet. Furthermore, it was off by different amounts in different directions. So much for accuracy. It was no wonder that it was a waste of time aiming at a target three hundred feet away.
Robins immediately asked himself why the accuracy was so poor. There had to be a logical reason. He finally determined that the problem had to do with the spin of the projectile. Spin was not given purposely; nevertheless, when the bullet emerged from the barrel it had some spin, and this spin was different for each projectile. The reason for it was that the spherical projectile was purposely made slightly smaller than the diameter of the barrel, and as it moved down the barrel it struck the sides of the barrel at various points, and each time it hit, its spin changed. The critical change, however, was the last one just before it emerged from the barrel. This would be the spin it had in flight. And Robins assumed (correctly) that this spin was interacting with the air that the projectile was passing through, and this interaction affected its trajectory.
The next problem, then, was to determine the bullet's speed as it emerged from the barrel, and, if possible, its spin. To determine its speed, Robins invented what is called a ballistic pendulumâone of the most important inventions in the history of gunnery. He began by clamping a musket in position. Directly in front of it he placed a large block of wood that was mounted at the end of a wire or rope so that it could swing like a pendulum. Robins found that when the gun was fired the block absorbed the kinetic energy of the musket ball, and, as a result, the block swung through a few degrees on the supporting wire. The kinetic energy of the bullet was being changed into potential energy in the process. Equating the two types of energy, Robins solve the equation for the velocity of the projectile, and he determined that the musket ball had struck the block with a velocity of 1,139 miles per hour. After all of the years that guns and cannons had been used, this was the first time anyone had any indication of how fast the bullets were going. So it was, indeed, a tremendous feat.
Now that Robins had determined the muzzle velocity of the gun, he had to figure out what happened as the projectile traveled through the air to its target. How was its velocity altered? By moving the block of wood farther away from
the barrel, Robins could find out. And it was soon obvious to him that the bullet was losing velocity rapidly. In fact, a bullet lost almost half its initial speed in the first hundred yards. The air through which the musket ball moved was obviously having a serious effect. Scientists and engineers of the time knew that air caused drag on a musket ball, but they didn't realize how dramatic the effect was. The basic problem was the shape of the projectile: a sphere. A sphere was not as aerodynamic as other shapes, and Robins soon realized this. What was the best shape to minimize atmospheric drag? The answer, at least to some degree, was already known. Archers had experimented with different types and shapes of arrowheads over the years, and they had found that the most dynamic arrow tip appeared to be one that was elongated and shaped to a point. But there was a problem with an elongated musket projectile with a point. It would tumble as it moved through space, making things even worse.
Robins analyzed the problem carefully, and, in doing so, he realized that there were actually two problems: finding the most aerodynamic projectile, and getting rid of the random spin as it left the barrel of the gun. Robins soon found that he could solve both of these problems with one significant change. He would give the bullet an elongated form with a pointed end, and he would cause it to spin around an axis through its center in the elongation direction. The best way to do this was to score the inside of the musket barrel with a series of spiraled grooves. In other words, he decided to “rifle” the barrel. But the grooves would only workâgive the bullet is spin along its central axisâif the bullet fit into the grooves. In short, the grooves had to bite into the lead as the bullet moved down the barrel. In fact, it was soon shown that the ideal size for a bullet was slightly larger than the diameter of the barrel.
Finally, Robins drew up plans for a breach-loaded gun; this was a gun in which the breach could be opened so that the charge of powder and a bullet could be inserted into the barrel. With the powder and bullet in place it could then be securely closed so that it was ready for firing. This was a significant breakthrough, but it wasn't actually used until several years after Robins's death. Rifled muskets were a problem technologically, so they didn't really take off for another few years. Nevertheless, Robin's breakthrough revolutionized military warfare, and it soon made England one of the strongest countries in Europe.
THE FLINTLOCK
The basic musket of the time also underwent a significant change during this era. The change was introduced early in the seventeenth century, and by 1660
the new musket became the major European military musket, and it continued to be used until about 1840. Most muskets of the time had smooth barrels and fired lead balls. They had a range of about 150 yards, and they weighed about ten pounds. When rifling began to be used on the barrels it gave them considerably better accuracy and a much greater range. But for the most part, rifled muskets were used only by sharpshooters (or what we might call snipers). The problem was that the rifled musket took much longer to load because of the use of tight-fitting bullets. Furthermore, the barrels of the rifled muskets (now called “rifles”) had to be cleaned after each shot, and this took too much time.
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The major difference in this new rifle, called the flintlock, compared to the wheel lock, was the use of a piece of flint to create sparks. A person firing a flintlock would cock the gun by using his or her thumb to pull a lever back against a strong spring (see diagram). At the end of the lever was a piece of flint with a point on it. As in the case of previous guns, the flintlock had a flash pan that was loaded with finely ground gunpowder. When the flash pan was primed it was closed. On the top of the flash pan was a steel striking plate called a frizzen, and when the trigger was pulled, the spring would force the flint down toward the plate. When it struck the frizzen it caused the pan to open. And as it slid down the frizzen it created a shower of sparks. The sparks would ignite the powder in the flash pan. As a result, a flame would flare down through the touchhole and ignite the charge in the barrel.
Close-up of the flintlock mechanism.
The flintlock mechanism was used on both rifles and pistols. By now, in fact, military pistols were becoming quite common; they had a relatively short range, but they were easy to handle, which made them popular with the cavalry. The smaller flintlock pistols were about six inches long; larger ones were about sixteen inches long. One of the most popular pistols was the Queen Anne pistol. This elegant and beautifully designed gun was frequently the weapon of choice for dueling, which was a popular method of solving arguments at the time. Indeed, some of the pistols even had two, three, or more barrels for quicker shooting.
Although they were a significant improvement over matchlocks and wheel locks, flintlocks had problems of their own. The flint had to be sharp or the gun would misfire. Also, the flintlock was vulnerable to moisture and accidental firing. In addition, occasionally the gun would explode in soldiers' hands.
CHRISTIAAN HUYGENS
Getting back to the physics of the era, we have one of the greatest physicists to appear after Newton. Unlike Robins and some of the scientists we've discussed so far, Huygens was born into a highly respected and relatively rich Dutch family; his father was a diplomat and part-time natural philosopher who played an important role in Christiaan's early education.
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Christiaan was schooled at home by some of the best local teachers until he was sixteen. It was obvious that he had considerable ability in mathematics, and this came to the attention of a family friend, the eminent mathematician Rene Descartes. Descartes encouraged Huygens to study mathematics at the University of Leiden. And indeed, Christiaan studied mathematics as well as law at the university, beginning in 1645. Over the next few decades he made numerous discoveries in physics, mathematics, and even astronomy, and although they had little effect on the military weapons of his time, his discoveries would have a tremendous influence later on.
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In addition to fundamental contributions to mathematics that included the first book on probability theory and solutions to many of the basic mathematical problems of the day, Huygens made major contributions to physics. In 1659, for example, he derived a formula for the force (now called the centripetal force) associated with circular motion, as in the case of a ball whirling at the end of the string. His formula stated that F = mv
2
/r, where m is mass, v is velocity, and r is radius. He also made fundamental discoveries relating to the elastic collision of two bodies; he was the first to show experimentally that the total momentum
before the collision is always equal to the total momentum after the collision (as predicted by Newton's third law). In addition, he invented the first pendulum clock, and he was the first to derive the formula for the period of a pendulum. He also devised new methods for grinding lenses and making telescopes, and he used telescopes to discover the largest moon of Saturn, now named Titan. He also observed Saturn's ring and predicted correctly that it was thin and not attached to the planet.
In the area of physics, however, he is probably best known for his wave theory of light, which he proposed in 1678. A few years later Newton suggested that light was composed of tiny particles he called corpuscles, and for many years there were two theories about the nature of light: one based on waves, and one based on particles. In 1801 Thomas Young showed that Huygens was correct, but today's quantum physics has embraced the concept of waveâparticle duality, since light seems to exhibit both properties, depending on one's method of observation.
Huygens also developed a balance spring for clocks and watches that is still used in some modern devices, and in 1675 he patented the first pocket watch. In 1673 he began experimenting with a combustion engine, which he fueled with gunpowder. It was not successful, but he designed a simple form of steam engine that was helpful to James Watt in his work.
PHYSICS AND THE INDUSTRIAL REVOLUTION
As mentioned earlier, a number of scholars have suggested that pure science (including physics) played only a minor role in the development of the Industrial Revolution. But if you look at the overall picture, it's easy to see that many fundamental discoveries in physics took place during this time, most notably those of Huygens. In addition, both the Royal Society in England and the French Academy in France were formed. The goal of both organizations was the enhancement of pure and applied physics. And although enhancement of the military was not a major goal of either, it was no doubt a secondary goal.
Another important advance during this time, which no doubt helped Watt's steam engine, was a formulation of the fundamental gas law now known as Boyle's law. It states that the product of pressure and volume is constant for a given mass of confined gas, as long as the temperature is constant. This means, for example, that when the volume of the gas is halved, the pressure is doubled, or if the volume is doubled, the pressure is halved. It was first stated by Robert Boyle of England in 1662.
Watt's work, in turn, was critical to military development in that it made the production of both cannons and muskets much more efficient. Furthermore, as mentioned earlier, a major branch of physics, namely thermodynamics, was created as a result of Watt's work on the efficiency of engines.
Huygens's work on collisions and the centripetal force was also helpful in relation to the development of weapons of war, but it was his work on light, and his suggestion that light was a wave, which would eventually have tremendous implications. A few years later, with the work of Maxwell and Hertz, it would lead to the discovery of the electromagnetic spectrum, which would eventually have a very large impact on war.