The concept of the game is incredibly simple: enter an angle and a velocity, click the "Throw" button and the projectile flys toward the other player. Getting a direct hit ends the round and winning enough rounds wins the game. Remember to allow for wind (check the arrow in the top left corner). Some projectiles are more exciting than others, it is possible to kill yourself with a badly chosen throw. Here is a rough guide to the angles.
There does seem to be a bug in it, sometimes you need to start a new game if it just hangs up at the start of a throw with no response.
Artillery calculations were of interest right through the Middle Ages, in an attempt to improve the accuracy and range of siege weapons. The first successful use of large scale canon bombardment was the last siege of Constantinople, and the attackers had plenty of time to get their aim straight, seeing as how the cannon was firing against stone walls, non-stop for 49 days in 1453 AD.
On the eleventh of April the Sultan had his cannon placed near the walls, by the weakest part of the city, the sooner to gain his objective. These cannon were planted in four places: first of all, three cannon were placed near the palace of the Most Serene Emperor, and three other cannon were placed near the Pigi gate, and two at the Cressu gate, and another four at the gate of San Romano, the weakest part of the whole city. One of these four cannon which were at the gate of San Romano threw a ball weighing about twelve hundred pounds, more or less, and thirteen quarte in circumference, which will show the terrible damage it inflicted where it landed. The second cannon threw a ball weighing eight hundred pounds, and nine quarte in circumference. These two cannon were the largest that the Turkish Khan had, the other cannon being of various sizes, from five hundred pounds to two hundred pounds, and smaller still.
Galileo Galilei (1564 to 1642) calculated that the trajectory of a projectile was a parabola, but he completely ignored air friction and wind resistance. Galileo's work was mostly focused on astronomy and the orbits of planets and moons which exist in the vacuum of space (although it is difficult to recognise how much was understood about the vacuum of space at this time, given than no one had experimentally constructed a vacuum on Earth yet).
As time progressed, the use of fire arms became more popular and technology improved. Infantry armed with muskets and cannons, as well as the ability to use ships as mobile gun platforms gave the colonial powers of Europe a huge advantage over everyone else in the world, up to and including the 19th century.
Sir Isaac Newton is often remembered as the man who "discovered gravity", although there is no doubt that many people had already noticed gravity long before Newton ever did!
Newton's real work was to codify the inverse square law of gravity and a system of equations of motion, along with a method for using these equations (known as the calculus). Newton also demonstrated (in theory, but not in practice) that a canon with sufficient power could fire a ball right round the earth landing it back where it started again.
A major forward step was the use of rifled barrels with a parabellum bullet rather than the traditional smooth barrels and ball shot of earlier muskets. The 1742 book (new edition in 1805), New Principles in Gunnery, by Benjamin Robins and James Wilson and Charles Hutton brought a more scientific approach to the field of ballistics (most notably allowing for air friction), including calculation of various range tables and optimal angles of elevation for guns, plus an explanation of why rifled barrels improve the accuracy of the weapon.
I must add, that the sole advantage of rifled pieces, is their preventing this irregularity; for by the spiral turns of the rifle, closely confining the bullet, they give it a rolling motion round an axis, which is coincident with the line of its direction, by which means its resistance is equal on every part of the surface, that goes foremost; and if a small inequality should at any time intervene, it will be presently rectified by that part shifting to the contrary side of the axis.And this is agreeable to what has been universally practised in relation to arrows; for the feathers of an arrow (as is well known to archers) are always placed in a spiral form, so as to make an arrow spin round its axis, without which their eye-sight would inform them, that the arrow undulated in the air, and did not keep accurately to its direction. This principle is confirmed too by the necessity, which every school boy finds himself under of making his shuttlecock spin.
During the Napoleonic Wars (1803 to 1815), artillery was the most feared weapon on the battlefield (but still not particularly accurate). Alexander Cavalie Mercer described the effect of a point-blank artillery barrage against charging heavy cavalry in recollection of the Battle of Waterloo:
I thus allowed them to advance unmolested until the head of the column might have been about fifty or sixty yards from us, and then gave the word, "Fire!" The effect was terrible. Nearly the whole leading rank fell at once; and the round shot, penetrating the column carried confusion throughout its extent ... the discharge of every gun was followed by a fall of men and horses like that of grass before the mower's scythe.
This US Army Ordinance Textbook (from 1920) covers the details of the modern method for calculating trajectories (which is all computerised now, but back then someone had to do it all by hand).