The Catapult

HISTORY

Throughout the history of the world, humankind has endured numerous destructive wars. While war was never a desirable choice for civilizations, societies have always felt compelled to be prepared for an attack. This constant pursuit of preparedness has produced numerous technological advances. One such innovation was the catapult.

Ancient Greeks and Romans were the first to perfect this device. Their catapults were capable of throwing a 60-pound rock further than the distance of five football fields. It took great ingenuity and skill to design and build a device that harnessed such a tremendous amount of energy.

Over 2000 years ago, the Greeks and Romans did not know about gunpowder, yet were able to hurl projectiles over a large distance using kinetic energy storage devices. Through the years, some modifications were made to increase the accuracy and throwing distance of these machines. The first two types of throwing machines were the catapult and the ballista. The catapult started out as a large crossbow to shoot oversized arrows at an enemy. The ballista was about 10 times larger than a catapult and threw large stones.

The ballista’s design consists of two pieces of wood, each fastened at one end to a torsion device rotating about a more or less horizontal axis. The free ends of the wooden pieces are connected together with a rope. The projectile to be thrown is held by the connecting rope used as a sling.

The choice of the Middle Ages was a trebuchet. This device used gravity instead of torsion springs to provide propulsion energy. The theory is simple: Put a large weight at the short end of a lever arm and put the projectile in some kind of basket at the other end of the lever. The velocity of the projectile can become quite large when the ratio of the lengths of the lever arms is great. Incidentally, the trebuchet was also used as a punishment device called the ducking stool. People were placed in a seat at the long end and successively dunked into a pool of water.

Modern catapults are based upon design principles derived from the early Greek and Roman catapults. The catapult is still in use today, although radically different from those used in history. The modern catapult is used to launch aircraft from the deck of an aircraft carrier. The aircraft carrier catapult uses steam as a source of energy to push a piston along a linear track in the aircraft carrier’s deck. The piston pushes the aircraft and accelerates the plane up to flying speed in a very short distance. The same kind of mechanism can be found at Knott’s Berry Farm, where it propels the Montezuma’s Revenge roller coaster ride.

THE CATAPULT DESIGN CHALLENGE

You will be given a collection of supplies from which you will build a catapult.  You may add only common household items to these supplies.  (If you are unclear if an item is allowed, check with your teachers first.)  It must be able to work consistently, regardless of who operates it.  Anyone should be able to use your catapult and make it work.  If your catapult only works if you launch it, then the design is not very good. The device must be capable of being operated through the use of a trigger device and each catapult design may employ only one power source.

OBJECTIVE

Research, design, and construct a catapult. Your design must be able to launch a Ping-Pong ball from a tabletop onto a box placed at least 6 feet away on the floor.

OR

Research, design and construct a catapult that will launch a practice golf ball from a table top the maximum distance.

MATERIALS:

  • Cardboard
  • Paper
  • Plastic spoons
  • Rulers/Tape measures
  • Masking tape
  • Rubber bands
  • Craft sticks/Balsa wood
  • Kite string
  • Scissors, glue, fasteners
  • Hand saws/Drills/Wood files
  • Finishing nails
  • Straight pins
  • X-acto knife
  • Protractors
  • Compass
  • Gum eraser
  • Ping-Pong ball
  • Practice golf ball
  • Additional objects found from home approved by the teacher

CRITERIA

Your success on this challenge will be based on your completion of the activities below.

  1. Your participation in the activity
  2. The accuracy of your CAD drawing
  3. The model construction
  4. The performance of your design. 

PROCEDURE:

  • Research catapults and other war machines from the past.
  • Summarize the history and mechanics of the catapult.
  • Using sketches and drawings develop a design that provides an adjustable launch and a triggering mechanism design
  • Make the final design of the catapult using CAD
  • Construct a working model of a catapult using only the materials provided
  • Conduct tests and modify the catapult acquire the best performance
  • Present your design.
  • Complete a PowerPoint presentation over this experience.

RESEARCH POWER POINT PRESENTATION

You will create a slide Power Point presentation, which may include the following slides:

  • Title slide for your catapult
  • A brief history of catapults and their use in medieval times. 
  • Different types of catapults (Ballista, Mangonel, Onager and Trebuchet), how they work, what they were made of, and what they were used for.
  • Terms and words used in the making and design of the catapult.
  • It should contain at least 3 pictures. Every picture should contain its (URL) in small font type.
  • The presentation can describe the ‘pros’ and ‘cons’ of different types of catapults.
  • You can also choose a favorite catapult style and provide an explanation for your choice.
  • Modern uses for catapults
  • A dimensioned CAD drawing of your design
  • List of materials used
  • List changes made to improve your catapult
  • Create a slide to show the members in your group
  • A conclusion of presentation should give information about your experience making the catapult
  • A bibliography slide for an Internet bibliography with ‘live’ links

NOTE: Presentation should have custom animation on each slide and transition but no sound.

You will be graded on the following items:

  • Your participation in the activity
  • The accuracy of your CAD drawing
  • The construction of the catapult
  • The performance of the catapult
  • The organization and presentation of the PPT

 TERMS TO KNOW

Trajectory - The path or curve described by a body (as a planet or projectile) under the action of given forces.

Potential Energy - Is the kind of energy that a body has by virtue of its position. When a body is raised to a higher level, it is able to do a certain amount of work in falling back again, and hence it was given a certain amount of potential energy in raising it.

Kinetic Energy - Is the energy that a body has by virtue of its motion.

Trigger - The device used to release the catapult once it has been loaded and charged to fire the projectile.

Ballistics - The science of projectiles.

Range - Distance for which a projectile can be thrown.

 

CATAPULT LINKS

http://www.howstuffworks.com/question127.htm

http://www.trebuchet.com/

http://www.tasigh.org/ingenium/physics.html

http://www.xenophongroup.com/montjoie/ngp_arty.htm#catapult

http://members.iinet.net.au/~rmine/gctrebs.html

http://www.pbs.org/wgbh/nova/lostempires/trebuchet/

http://www.castlewales.com/siege.html

http://members.iinet.net.au/~rmine/htt/ttspot.html

http://www.redstoneprojects.com/trebuchetstore/trebuchet_history.html

http://www.lcse.umn.edu/specs/labs/catapult/practice.html

 


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