Cycle 2 Week 22 Hands-On Science script for all ages - Popsicle Stick Catapults, by Robyn Cooper Today we are going to think like engineers. Engineers use science, math, and even art to solve problems. Our problem is to launch an object using a catapult. Before we start science today, let’s sing the scientific method. [Sing the song, to the tune of Pop Goes the Weasel. “The Scientific Method is Question, Research, Hypothesis, Experiment, Analysis (clap!) and conclusion.” We are going to talk about building catapults today. What’s our Question? How can I think like an engineer to build the type of catapult that launches an object the farthest possible distance? • Now, what makes a catapult, a catapult? Let the kids brainstorm. A catapult is a ballistic device used to launch a projectile a great distance (without the aid of gunpowder or other propellants) – particularly various types of ancient and medieval siege engines. Have you heard of a slingshot? That’s a catapult! Remember David and Goliath? He used a sling and a rock to knock that giant down! • What problems do catapults solve? Let the kids brainstorm: They allow someone to launch objects far distances. The catapult is a simple machine. Primitive catapults were the product of relatively straightforward attempts to increase the range and penetrating power of missiles by strengthening the bow which propelled them. • What do engineers need to consider when they are designing a catapult? Tell kids, “Don’t answer this yet, we’ll come back to it.” Let’s do our research. There are three main questions to ask in our research: • What are the parts of any catapult? • What kinds of catapults are there? • What is the science of catapults? But to answer this last question, let’s first think about what kind of work does a catapult have to do? Let’s talk about parts of a catapult first (see below). The 4 main components of a catapult are lever or arm, the base, the tension source, and the basket. the projectile is not an actual part, but it is needed. The tension source could come from a number of places. Here are two different examples. What kinds of catapults are there? (See images below). I’ll tell you about four basic kinds. Mangonel -The earliest catapults date to at least the 4th century BC with the advent of the mangonel in ancient China. It’s a type of traction trebuchet and catapult. The mangonel operated on manpower pulling cords attached to a lever and sling to launch projectiles. This machine was designed to throw heavy projectiles from a "bowl-shaped bucket at the end of its arm". Mangonels were mostly used for “firing various missiles at fortresses, castles, and cities,” with a range of up to 1300 feet. These missiles included anything from stones to excrement to rotting carcasses. Mangonels were relatively simple to construct, and eventually wheels were added to increase mobility. Trebuchet - A trebuchet (French trébuchet) is a type of catapult that uses a swinging arm to throw a projectile. It was a common powerful siege engine until the advent of gunpowder. There are two main types of trebuchets. One is the mangonel you just learned about. A trebuchet works by using the energy of a falling (and hinged) counterweight to launch a projectile (the payload), using mechanical advantage to achieve a high launch speed. For maximum launch speed the counterweight must be much heavier than the payload, since this means that it will "fall" quickly. Trebuchets were probably the most powerful catapult employed in the Middle Ages. The most commonly used ammunition were stones, but "darts and sharp wooden poles" could be substituted if necessary. The most effective kind of ammunition though involved fire, such as "firebrands, and deadly Greek Fire". Trebuchets came in two different designs: Traction, which were powered by people, or Counterpoise, where the people were replaced with "a weight on the short end".[44] The most famous historical account of trebuchet use dates back to the siege of Stirling Castle in 1304, when the army of Edward I constructed a giant trebuchet known as Warwolf, which then proceeded to "level a section of [castle] wall, successfully concluding the siege”. The onager was an imperial-era Roman torsion powered siege engine, or a small catapult. The onager was first mentioned in 353 AD by Ammianus Marcellinus (a Roman soldier and historian), who described onagers as the same as a scorpion. Ballista - plural ballistae, sometimes called bolt thrower, was an ancient missile weapon that launched either bolts or stones at a distant target. Ballistae were similar to giant crossbows and were designed to work through torsion. The projectiles were large arrows or darts made from wood with an iron tip. These arrows were then shot "along a flat trajectory" at a target. Ballistae were accurate, but lacked firepower compared with that of a mangonel or trebuchet. Because of their immobility, most ballistae were constructed on site following a siege assessment by the commanding military officer. Other uses in history: Early Greek catapults emerged around the 1st century BC. Early uses were also attributed to Ajatashatru of Magadha in his war against the Licchavis. He was a king of the Haryanka dynasty of Magadha in East India in the 4th Century BCE (492 to 460 BCE). Ancient Indian emperor Ajatashatru of Magadha used catapults against the Licchavis. King Uzziah, who reigned in Judah until 750 BC, is documented as having overseen the construction of machines to "shoot great stones" in 2 Chronicles 26:15. “15 In Jerusalem he made devices invented for use on the towers and on the corner defenses so that soldiers could shoot arrows and hurl large stones from the walls. His fame spread far and wide, for he was greatly helped until he became powerful.” Leonardo Da Vinci’s Catapult - His design incorporated a large wooden leaf spring as an accumulator to power the catapult. Both ends of the bow are connected by a rope, similar to the design of a bow and arrow. The leaf spring was not used to pull the catapult armature directly, rather the rope was wound around a drum. The catapult armature was attached to this drum which would be turned until enough potential energy was stored in the deformation of the spring. The drum would then be disengaged from the winding mechanism, and the catapult arm would snap around. Mongol warriors using trebuchet to besiege a city Modern Use The last large scale military use of catapults was during the trench warfare of World War I. During the early stages of the war, catapults were used to throw hand grenades across no man's land into enemy trenches. They were eventually replaced by small mortars. Tell me about World War I Leaders. World War I leaders. Celemenceau of France, Lloyd George of England, Nicholas II of Russia, Wilhelm II of Germany, and Wilson of the United States were leaders during WWI. Tell me about World War I Countries. During WWI Great Britain, France and Russia were allies and fought against Austria-Hungary and Germany, which were called the Central Powers. In 1917, the United States entered the War assisting the Allies. Aircraft catapult Special variants called aircraft catapults are used to launch planes from land bases and sea carriers when the takeoff runway is too short for a powered takeoff or simply impractical to extend. Ships also use them to launch torpedoes and deploy bombs against submarines. Small catapults, referred to as "traps", are still widely used to launch clay targets into the air in the sport of clay pigeon shooting. Okay, now we are ready to discuss the science of catapults. Without the use of an explosive, what kinds of action could build up potential energy? springs, bows, twisted rope, elastic, or any of numerous other materials and mechanisms. A catapult uses the sudden release of stored potential energy to propel its payload (whatever it is launching). Let’s go over our facts about energy! What are two forms of energy? Two forms of energy are Kinetic and Potential! What is potential energy? It’s stored energy! In catapults, the three primary energy storage mechanisms are tension, torsion, and gravity. We learned what tension is during our bridge building contests. What is tension? Tension is a pulling or stretching force, acting outward. We learned about torsion when we did our experiments on week 16. Then the center of gravity is off the mass center, the object wants to spin. That’s torque… similar to torsion1. Most convert tension or torsion energy that was more slowly and manually built up within the device before release. Okay, so catapults launch a payload. The operator wants the payload to go far! What force is the payload fighting? Gravity! GRAVITY! Yes! Let’s go over our gravity facts again. 1. Objects with mass are attracted to each other, this is known as gravity. Think of it like a magnet. 2. Now, does weight impact speed? Remember Galileo and his experiment on the Leaning Tower of Pisa? NO! The weight of something does not impact its race to the ground! Yes, catapults fight gravity… and something else… Force. What are the laws that govern motion? Catapult designers also had to fight the laws of motion… these laws of motion were identified much later, by the way, because Newton was around in the 1600s. Also, let’s recall Newton’s First Law of Motion. Who knows it? 1 Torque is a measureable concept, whereas torsion is a concept, which is mathematically projected by the shear stress or the twist angle.