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A "Lethal Enforcer":

An Alexander Hamilton Ballista



The Project


This project was conceived and developed as part of the curriculum by Physical Science teacher, Jaime Scott of Alexander Hamilton Middle School in Houston, Texas. The participants in the group are: Fallon Lawrence, John Leavitt, Emeshako Neal, Jennifer Rodriguez, Sara West, also known as The Legions.


The Legions


Fallon Lawrence

John Leavitt

Emeshako Neal

Jennifer Rodriguez

Sara West

Here's Team Legions. Each member contributed countless hours and effort towards the project. They were rewarded when they tested out their ballista with a tennis ball before their peers and their projectile traveled 45 yards at zero elevation. Their peers were amazed!

Here is the Ballista under contruction and poised to fire its ammo.


Physical Concepts Behind the Ballista

Newton's First Law - This law states that an object moving at a constant velocity keeps moving at that velocity unless a net force acts on it. The water balloon that is thrown by the ballista keeps moving at a constant velocity until air resistance slows it down.


Newton's Third Law - This states that for every action there is an equal and opposite reaction. The sling gets pulled back and when it is let go, it gives an equal and opposite reaction. The torsion arms bend forward when the sling is pulled forward and when the sling is let go, the torsion arms go back with an equal and opposite reaction.


The Conservation of Energy - This causes the flying water balloon to slow down. Friction and air resistance causes the water balloon to slow down and fall.


Description of Simple Machines


Levers: A simple machine consulting of a bar that is free to swivel (rotate) around a fixed fulcrum.


Pulleys: A simple machine consisting of a grooved wheel with a rope or a chain running along the groove.


Wheel and Axle: A simple machine consisting of two different sized wheels that rotate together; such as a doorknob or a wheel-handled faucet.


Transformation of Energy


As you know, energy involves just about everything you see or do. Energy is the ability to cause change. There are different types of energy; such as kinetic energy, (which is used primarily in our project), potential energy, and work. Yes, work is a type of energy. The transfer of energy through motion.


The ballista ammo goes off with a little kinetic energy and a lot of potential energy, but like most moving objects, it increases in kinetic energy as it goes off.


Mechanical Advantage of a Lever


IMA = length of effort arm / length of resistance = Le / Lr


ex. IMA = 10 in. / 2 in. = 5 / 1 = 5 IMA = 5


A torsion arms' ideal mechanical advantage is 5.

Inclined Plane: A simple machine consisting of a sloping surface (ramp) used to raise objects.


What follows is a brief story and history of the ballista.


Little Man, Big Thoughts


Once in the small town of Naples, there lived a young man named Vladamir. He was very talented and always in his studies. He had a great personality but because he was not very popular, he was thought of as being quiet and shy, no one really understood him not even his family. So Vladamir spent a lot of time alone even though he didn't enjoy being alone. As he got older, he found more and more interesting things to do. He enjoyed reading about war tales. Vladamir was probably one of the smartest or the smartest person in time.

Now the province of Naples was having many problems with the great nation of Ukelele, which surrounded Naples. The Napelians wanted to be independent, and wanted to keep their land. Ukelele on the other hand wanted the land the province was on. They believed right under the Napelians very feet was gold. The heads of Naples received many letters of threat from the heads of Ukelele. The threat was that if they didn't give up their land peacefully, they would have to start a war and take no prisoners. The Napelians had heard of Ukelele's weapons. They wanted to avoid war but they certainly were not going to obey their commands.

Vladamir and a good percent of the town knew about the rivalry going on. Panidlock, the general of the Naples army began to recruit soldiers. Vladamir with his knowledge of books of previous wars and techniques wanted to help. He wrote about the matter. They read it before dinner. During their meal, his mother responded by saying," Vlad, dear, we are very proud that you want to help, but the truth is that your too young. Your father is going and that is good enough. If something were to happen to him, you must take care of us." Vladamir was heart broken. He thought of all the things they might say, but he never thought that would be one of them. Vladamir had a dream that night that inspired him to help his army. He dreamt that he was in a hole trying to climb out, but familiar faces, including his family, kept pulling him downward. Vladamir took from his dream that everyone was pulling him back, and he must make it out of that hole even if it meant going against highly respected people, or those he loved.

The soldiers of Naples were to go to war on May 12, it was a month till then. Vladamir had so many ideas he thought would help, one of which a potential catapult. He worked hard on it at three every night. He would go to sleep at one/half a mile from Ukelele. On May 1, he had finished it. Vladamir had everything planned out perfectly. On the night of the 11th, Vladamir went into the forest and waited in his father's armor that he had stolen.

Vladamir went into a deep daze, imagining how everything would happen. He imagined thousands of men marching toward the town. Then he saw himself catapulting an exploding bomb in the crowd. Vladamir stood with brilliance and courage and with a little help from the Napelian army, Naples defeated Ukelele and won their independence.


The Ballista:

A Historical Overview


The story of the ballista began in Ancient History. Man was developing weapons to destroy his enemy. He developed slings to hurt and maim others from afar in the Third Century B.C. Not soon thereafter the thought of projecting rocks and arrows across great distances became an obsession. With this creative thinking process, Man developed the spear and bow and arrow. After many years had passed, the Greeks, led by the great Archimedes, evolved the spear into pikes and, with many years spent in contemplation, the siege engine. At Syracuse, the first siege engines were tested against the young Roman Navy. The audacity of the Greeks made the Romans believe the Gods were hurling boulders at them. To say the least, the Romans ran. By the year 400 B.C., the Romans had developed their own siege weapons, including the Manuballista, Auroballista, and the crossbow, which was, essentially, a small catapult. The ballista was, in essence, a crossbow of gigantic proportions, and could propel a rock at speeds that could go through both bone and metal. Near the fall of the Great Roman Empire, the hand crossbow had been invented, for the glory of Rome, of course. The hand crossbow was not as powerful as the ballista, but it was portable. After the fall of the Roman Empire, ballistas were unused, until the Middle Ages when they were used for a short period of time. After the Middle Ages, the great ballista was replaced by gunpowder and returned as stories and toys for young and adults alike.


Roman Catapults

The Cheiroballista


Most catapults used by the Roman army were products of Greek minds in one way or another. The catapults of the Roman Army were either obtained from Greek cities, built by Greek craftsmen, or built by Roman handymen to Greek specifications (10). The chieroballista, and its derivatives the manuballista and the acruballista represent one of two types of artillery engines the Romans created themselves during the second and third centuries of the common era.

The cheiroballistae was a small but powerful arrow throwing engines mounted on a wheeled carriages that allowed it to be quickly maneuvered (11). The manuballista was small torsion arrow throwing engine, similar to the Cheiroballista only without the wheeled carriage. The acruballista was a very small non-torsion engines, the smallest of which were handheld (12). This engine was the fore-father of the crossbow which was reintroduced to Europe by the Norman's close to six hundred years later. Each of these engines represent the Roman Army's adaptation of Greek catapult technology to better suit their needs.

Designed to be more mobile, yet as powerful, as the small Greek catapults, the cheiroballista and manuballista were constructed with several modifications to better suit the engines role in supporting the Roman infantry. To start, the engine were smaller. To save weight and girth the hole carrier was redesigned into a metal frame in the place of the cumbersome wood hole carrier of the Greek design. The omega-shaped support beam at the top of the hole carrier was called the arch. Its curved design provided artillerymen with a greater field of vision when aiming the weapon making it much easier to pick moving targets in the distance.

Beyond these basic structural differences the cheiroballista worked just like the catapults before it. The two arms stuck through the sinew skeins of the cheiroballista were cranked back with the aid of a winch and were released by a claw shaped trigger mounted on a dovetailed slider arrangement - all adapted from the Greek catapult.

This weapon made its first appearance during the Dacian Wars of Rome in the Second century, and appears to have worked well judging from its inclusion on Trajan's column.


10. Marsden, Historical Development, 174.

11. Werner Soedel and Vernard Foley, "Ancient Catapults," Scientific American, March 1979:160.

12. Marsden, Historical Development, 2.


©STAAC 1995, all rights reserved.

Special Thanks go out to Ray Charles Neal and Christopher Leavitt for their supervision and assistance in the construction of the Ballista and stand. Also to Ruben Rodriguez for assisting in the design and creation of the Ballista plans and web authoring.


Our inspiration comes from and many thanks go out to Team Carbo and the efforts of their catapult project. Click Here to go to Team Carbo's page.


Click Here to go to the Alexander Hamilton Middle School webpage.

Created by Jennifer Rodriguez on Monday, May 14, 1998.

For more information, please send e-mail to