Physics of Catapults Essay
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The ballista, or "shield piercer," was first developed by the Greeks using the same principles as a bow and arrow. Its primary use was to, as the name suggests, pierce enemy shields, since normal bows lacked the power to do so. Early versions of the ballista include the gastrophetes, which is nothing more than an enlarged bow that can be braced against the users body. http://members.lycos.nl/onager/GastrophetesPic.jpg
As time went on ballistas were improved to become larger and more powerful, eventually becoming mounted mechanisms that could be operated by two or more people. The Romans eventually modified them to throw stones, making them more effective in seiges against walled…show more content…
Using this relationship assumes that the force constant is constant, or that moving the arms back 2 meters gives twice the force that moving them back 1 meter would do, which is most likely not correct, but close enough for a general assumption of the force to be made. When the force is applied, the projectile is accelerated to the end of the ballista, at which point it released with a velocity v and an angle q from the horizontal. The velocity can be found using the kinematic equation v2=2ax, where a is the acceleration and x is the length of the ballista that the projectile is accelerated upon. Since F=ma and F in this case is -kd, the equation can be simplified into v2=2-kdx/m. After it is released, the projectile obeys the laws of projectile motion, disregarding air resistance. Therefore, the range of the ballista can be given by the equation
where g is the accleration due to gravity.
The Romans, finding the ballista difficult to construct, simplified the design and created the onager. It had one arm instead of two, and is what is most commonly identified as a catapult today. http://members.lycos.nl/onager/OnagerPic.jpg
During the Dark Ages, the French were able to re-invent the onager, and they called it the mangonneau, and it became known in England as the mangonel.
Catapult History and Modern Day Construction
By Baintighearn Aimiliona Tevnane CW
During the Middle Ages, many weapons were created to help aid in the winning of battles. As the castle walls became higher and stronger, a new way had to be invented to destroy them. One such weapon was the siege engine called a catapult. The term catapult was derived from the Greek word "katapultos". A catapult was a large machine on wheels with a basket attached to a long wooden arm and a power source for hurling projectiles on the other. The first catapult however was invented around 400 BC in Greek town Syracus. It was not the version seen so many times at our own wars in todays Society for Creative Anachronism.. The first catapult closely resembled a crossbow. It was called the Gastraphete, and worked similar to a crossbow. The Gastraphete had to be pointed at the ground and the operator had to use great force to set the weapon to fire. The Greeks were so impresses with the destruction this weapon caused, they created a bigger version of the Gastraphete. This was called a Ballista and was used more as a defense weapon against raiding armies. The machine had to be reloaded by many men, so the Greeks improved on the Ballista by building them with cranks on the end. Now only one or two men were needed to load the weapon and the others could continue the fight. The crank worked to pull the rope back putting the Ballista in the ready to fire mode.
Another type of siege weapon was the trebuchet, which is a form of catapult, but the power source was different. The trebuchet used gravity and weights to hurl the projectile. The catapult used in the Middle Ages was powered by one of four different sources. These were tension, torsion, traction, and gravity. Let's take a closer look at each power source and how it worked.
Tension powered catapults had a long flexible arm, so that when the basket was bent backwards to give the weapon its throwing power, the arm wouldn't break making the weapon useless in battle. The basket was tied or hooked in some way when bent backwards, so that large stones or other types projectiles could be loaded into the basket. When the basket was released the projectile would fly into the air hopefully hitting the castle wall and causing part of it to tumble to the ground. Sometimes flaming projectiles were put in the basket. Upon impact the ball would burst setting fire to everything in a given radius. The tension powered catapult was often used for destruction of castle walls, but sometimes it was used as a defense weapon from the castle itself. The tension catapult was able to throw and shoot farther than most other types. It was also a better weapon than the ballista, as the catapult was portable with it's wheels.
Torsion powered catapults such as the ballista used cranks to pull back the basket that held the projectile. Torsion was a form of power created when the rope of the Ballista was twisted to generate the force. The rope would get tighter and when released, the force would propel the projectile forward from the basket. The missile was propelled with such force that it could take out several armored men in one shot or do serious damage to a castle wall.
Traction powered catapults , trebuchet as they are commonly called, used people as the power source. The men would bring down the shorter end of the long beam or arm, causing the longer end of the arm to flip up, causing the basket to loose it's projectile towards the intended target. Some of these siege weapons were held by men and cause some difficulty in battle.
Gravity powered catapults simply used gravity to hurl the projectile. At its most basic understanding, a gravity catapult is simply a lever that uses centrifugal force to its advantage. Think of it as a modified seesaw. When two people are on the seesaw and both are of close weight, the see saw balances it's self. If another person came up and jumped on one end of the seesaw with one of the people, the single person on the opposite end is likely to become airborne. Like the seesaw, a gravity powered catapult is also pivoted in the middle. A counter-weight was built onto one end of the catapult and a basket or sling on the other. The projectile end was pulled down forcing the counter weighted end to rise. Once the projectile basket was released, gravity would pull the weighted end of the arm down, causing the projectile to hurl through the air.
Today, catapults of all kinds and sizes are used. We do not hurl projectiles at castles anymore, but we do build them to have fun. The next time you are at an event that has a siege weapon activity, watch how they work. They are used to hurl projectiles, but only to see what distance a projectile goes.
They are never used to hurl objects at people or buildings. So gather your supplies and step forward into the future of siege weapons!
Below you will find two versions of toy catapults. Each one when put together correctly will hurl a small object as it's counter part in the Middle Ages hurled large objects. Be sure to have adult supervision when creating the catapults and NEVER SHOOT A CATAPULT AT ANOTHER PERSON NOR SHOULD YOU EVER SHOOT HARD OR SHARP OBJECTS. Marshmallows make great projectiles as do grapes.
Catapult I: for older children
Adult supervision is highly recommended.
- one piece of 3/4 inch wooden board -9 (nine) inch long x 2 (two) inches wide
- 8(eight) Jumbo craft sticks 1 (one) popsicle size craft stick1 (one)- 6" (six) length of 1/8" diameter dowel rodding 1(one) spring action clothes pin
- 1(one) heavy duty rubber band 1(one) plastic spoon
- Wood glue Coping saw (finishing saw)
- Drill with 1/8 inch bit Screws and screw driver
- hardware brads 1/8 inch in length
Making the arm: Stack two jumbo sticks together. Measure and drill a hole centered 1/2 inch from from one end of the craft sticks. Using the saw, cut a 1 (one) inch long and 1/8" wide slit in the opposite end of the craft sticks.
For arm grippers: Cut 1 1/4 inches from each end of the popsicle sized craft stick. Cut a small piece of the craft stick for a spacer. Sandwich the grippers and the spacer between the arm pieces while gluing together. The cut ends of the grippers should be at a slight slant, 1/2 inch apart with the the first gripper 1/2 inch from the cut slot. Be sure to position the spacer 1/2 inch from the drilled holes at the opposite end of the arm. Break off the spoon handle, leaving 1 1/2 inches of the handle attached to the spoon bowl. Glue the handle part of the remaining spoon with the bowl into the slit in the arm. Set aside letting glue dry thoroughly.
Catapult Assembly: Glue 1(one) Jumbo craft stick 3 (three) inches from one end for the upright supports upright (perpendicular) to the base of the catapult to each side of the catapult base.
Glue 2 (two) jumbo craft sticks at an angel on each side of the base, allowing the glue to dry over night. Once the glue has dried, drill small holes for the brads in the base of the jumbo sticks where they attach to the catapult base on both sides. Hammer 1 (one) brad into each jumbo stick where it was glued to the catapult base. The brads will help assure the stability of the catapult construction.
Drill a hole 1/2 inch from the top of the stabilizers on both sides. Cut the dowel in half then carefully insert one half into the the holes you just drilled. Glue into place. This dowel will be the base of which your power source (the rubber band) will be attached to later.
Drill a hole 2 (two) inches from the bottom of the 2 (two) centered jumbo sticks (the upright ones). Slide remaining dowel half into one side of the uprights, through the arm and then through the remaining hole of the opposite side. Glue into place. Allow glue to dry.
Attach the clothes pin to the base of the catapult positioning it so that it can grasp the upper gripper when the arm is pulled down for firing. Insert the screw through the spring of the clothes pin and screw it securely into the board base. Attach the rubber band to the upper dowel securely looping the rubber band through itself. Slip the other end of the rubber band over the arm of the catapult nestling it between the grippers. Push the catapult arm down towards the base until the end gripper fits into the gripper end of the cloths pin. Load your projectile and squeeze the legs of the clothes pin to fire.
NOTES: The further the rubber band is placed down the arm, the more momentum the catapult will have.
Catapult II: for smaller children
- Heavy card board Strong glue
- 1 (one) small popsicle stick 2 (two) toilet tissue tubes
- heavy rubber band scissors
Cut the following squares from the heavy cardboard: 1 (one) 5 inch square for the base of the catapult, 1 (one) 3 inch square and 1 (one) two inch square. Set the 2 smaller squares aside. Glue the 5 inch square to the 2 (two) toilet tissue tubes. This will create the base of your catapult. Set the base aside and allow the glue to dry a bit. Now score the 3 inch square down the middle, being sure you do not cut through the square. Bend the 3 inch square in half like a book. Glue the popsicle stick to one half of the folded 3 inch square, under one folded side. Glue the 2 inch square to the opposite end of the popsicle stick. Once the glue has had a chance to set, carefully glue the unused fold of the 3 inch square a 1/2 (half) inch from one end of the 5 inch base. Allow glue to dry thoroughly. May take over night, unless using a hot glue gun. Once the glue is dry, cut the rubber band and make a small hole in the base of the catapult in the same end as the arm was placed and a small hole in the 2 inch square. Thread the opposite ends of the rubber band in each hole, and adjust it so that the arm has firing power. Make sure to tie knots in the ends of the rubber band so it will not slip out of the holes.
Congratulations! You just created a working model of a catapult.