For better or for worse, physics has always been involved in warfare. Both the machinery of the human body and the character of the theater of battle exist in the physical world, and therefore an understanding of the rules of the world can prove to be a decisive advantage in battle. This isn’t just true in the modern age of nuclear weapons, satellite reconnaissance, and laser-guided bombs. It’s been true at least since Newton’s mechanics were used to calculate the trajectory of artillery fire in the 17th century.
Those classical mechanics are still used in warfare today. The job of a modern sniper entirely depends on the physics which Newton discovered. We’ll just talk about one part of it today: bullet drop.
From our experience watching movies, we sometimes think that bullets travel to their targets instantly. The trigger is pulled and the bullet hits at essentially the same time. But for long-range shots, this is pure myth. An average handgun bullet travels well under the speed of sound. Rifle bullets (especially of the kind used for sniping) can travel at speeds of 3,000 feet per second, which is pretty close to triple the speed of sound. Fast as that is, it’s still a far cry from instantaneous at long range. The longest confirmed sniper kill was by a Canadian soldier named Rob Furlong fighting in Afghanistan, who killed a Taliban fighter at a range of just over 1.5 miles. Even at 3,000 feet per second, the bullet would still take about 2 seconds to reach its target. In reality the bullet only traveled at that speed as it left the rifle. Air resistance would begin slowing the bullet immediately, so in practice the time of flight would have been significantly longer. I’ve seen estimates of 4 seconds.
But just like a rock dropped from your hand, a bullet also begins falling once it’s been fired. The only difference is that it’s also moving forward at the same time. In 4 seconds the bullet would have fallen
some 256 feet. Therefore Rob would have to aim at a point 256 feet above the target he was trying to hit. How would he know that? Of course it’s impossible to do quickly the fairly difficult math of calculating the bullet flight time with air resistance in a combat situation. You’d at least need to know the specifics of the air pressure and wind, and the ballistic coefficient and initial velocity of the specific bullet being fired. It gets even more complicated because drag force is a function of velocity, and not a nice clean mathematically easy function either. Typically it’s more-or-less proportional to v2, but both the coefficient and the exponent tend to themselves be functions of velocity and time. Solving the differential equation analytically is generally impossible, but it can be done with numerical techniques. Fortunately the math has already been done by professional military scientists, and snipers are trained to use the results of those calculations which are printed on charts which they keep.
The skill required to bring off such a shot even with the help of physics calculations is astonishing. But it would be absolutely impossible without a strong understanding of physics.