Our workshop was devoted to designing different types of catapults using huge clothes pin style clamps, sawed pencils, pvc tubes and Gorilla tape. Those who missed the workshop can build their catapult at home. It is the first lesson on levers and fulcrums.
A lot can be learned from the simplest of catapults.
For those who did not get to make one and even for those who did, here are some catapults. Try to make one more.
The first three are links and the fourth is a diagram but no link.
Builds a frame and then the launcher. The video demonstration is further down the page on this site.
2A) RUBBER BAND AND POPSICLE STICKS ONLY
No actual frame. Just a beam and a launcher.
CLOTHESPIN VERSION
No actual frame. Just a beam and a launcher.
2B) Hot Glue and clothespin version - Can use masking tape Quickest version perhaps.
CLOTHESPIN VERSION
4) In this version, The fulcrum is in the middle as opposed to at the end of the launcher.
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It is important to have a fulcrum around which the launcher can rotate. Torsion can be created in a variety of ways: a metal spring, a wound up piece of string like a winch or a plastic or rubber band. There also needs to be a base. In one of the oldest catapults, a sling shot, human beings held the slingshot and formed the base and launched it. In the model we have a frame.
These are basic parts, but the crucial
weight and length of the projectile must be proportional to the size and strength of the torsion springs. The building of catapults brings together knowledge and skill in design, physics and mathematics/geometry.
You can also browse around the following website to find out more about how tension was created in catapults and projectiles during medieval times:
Vocabulary
Trajectory — The path or curve described by a body (as a planet or projectile) under the action of given forces.
Potential Energy — 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 — The energy that a body has by virtue of its motion. It is the amount of energy required to accelerate the mass from stationary to its current velocity. Catapults and bows held under tension are also examples of potential energy. The term applies equally to energy stored electrically, chemically and so on.
Energy Storage — If a
spring is compressed, and then is forced to stay in that compressed
configuration, the spring can be said to have “stored” energy. Once the
spring is released, it will return to its original configuration
(usually expending the stored energy as rapidly as possible). The same
goes for stretching a spring; when released, it will collapse back to
its original configuration.
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.
Prior to the discovery of gun powder, catapults were used for war.
5 TYPES OF CATAPULTS:
Background
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 cross bow 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.
When most people think of the catapult, they are actually thinking about an onager. The strange name is derived from a wild donkey kicking with its hind legs. The onager (or gone, mangonel, or nag) was typically a single spar held in a more or less vertical position by a torsion device rotating around a horizontal axis. The projectile was located in either a pocket at the top end of the spar or in an attached 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 ducked into a pool of water.
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.
( Courtesy: Cornell Center for Materials Research)
MORE RELATED SCIENTIFIC TERMS..
LAUNCH ANGLE, PULL BACK ANGLE
ALSO, IF YOU RECALL FROM A PREVIOUS WORKSHOP ON BRIDGES:
The resistant force felt when pulling the string/wire/elastic taut is called tension.
The resistance force felt when pushing on the ends is called compression.
FINALLY A QUICK OVER VIEW OF SIMPLE MACHINES
Here is a link that very briefly describes different types of simple machines.
Click on the examples to take a look at them.
Here is a link to a Rube Goldberg machine that uses concepts from simple machines to create a 34 step process to drink a glass of milk.
ZOOM - RUBE GOLDBERG
http://www.teachersdomain.org/asset/phy03_vid_zmilk/
Here is Bill Nye's mini movie series on Simple Machines
Bill Nye's Simple Machines
Here is a link to a Rube Goldberg machine that uses concepts from simple machines to create a 34 step process to drink a glass of milk.
ZOOM - RUBE GOLDBERG
http://www.teachersdomain.org/asset/phy03_vid_zmilk/
Here is Bill Nye's mini movie series on Simple Machines
Bill Nye's Simple Machines
