Catapult
History
The invention of the catapult is attributed to Dionysius the Elder, tyrant of the state of Siracusa, nowadays called Sicily, in Italy. In the 4th century BC, Syracusa was at war with Carthage, fighting for the Mediterranean Sea. It is said that Dionysius decided to hire the best engineers to develop new weapons. One of them was the catapult. Precursors of modern missiles, the catapults are nothing more than a mechanism that uses an arm to throw an object (usually stones or darts) a great distance. In general, these weapons were used in siege to castles and fortifications, with the aim of breaking the defense of the enemies. Over time, the catapults were being refined and became more efficient. An improved version is the trebuchet, which, instead of tensing or twisting a rope, uses gravity, by means of a counterweight, to launch larger projectiles at great distances. During the Middle Ages, there are records that catapults even served a rudimentary form of biological warfare. Carcasses of sick animals or even of people who had died of Black Plague were thrown over the walls of the castles to infect enemies. However, with the proliferation of the use of gunpowder and the development of cannons, catapults began to decline. Even so, they were still used during World War I for the throwing of hand grenades against enemy trenches.
Physics involved in the machine
The catapults use the concept of storing and releasing energy required to launch an object. They also use many physics concepts:
- Elastic Potential Energy: is the energy added to the compression or distension of a elastic object, that is, is the potential energy of a spring or rope with elasticity. The spring used in the catapult is stretched by storing energy.
- Kinetic Energy: As soon as the spring is released, the potential energy is transformed into kinetic energy, which by its is passed to the projectile it acquires
movement. - Elastic Force: is the force exerted by the spring on the launching arm of the projectile, if this arm does not cause deformation in the spring, as soon as this force is withdrawn, the spring returns to its original shape.
Building Process
Day One
On day one we decided which machine we were going to work with: a catapult. After that we started researching catapults and their building process, we thought in something different than a wooden catapult. That’s when we decided that we were going to it in a different way.
Materials:
- 2 soda cans;
- A pack of rubber bands;
- 2 pencils;
- Adhesive tape;
- Bottle cap;
- 2 coins.
Day Two
On day two, we brought all the materials and started working with them.
- Put the cans in the right position
2. Connect them with the rubber bands
3. Insert the fork between the the bands and the can
4. Join the two pencils with tape and put the fork between them
5. Put the cap on the tip of the fork with tape
The problem with our first try is that the cans were empty, so the cans kneaded and didn’t give the fork the elasticity necessary to work properly.
Day Three
We decided to put paper inside the cans to create volume, didn’t work. So, we decided to use sealed cans the next day.
Day Four
Now, with sealed bottles, the catapult worked well. We used the coins as the projectile.
References
http://www.midrealm.org/mkyouth/links/catapults.htm
http://www.ancient-origins.net/artifacts-ancient-technology/catapult-long-reaching-history-prominent-medieval-siege-engine-004418
https://www.real-world-physics-problems.com/catapult-physics.html
https://sites.google.com/site/physicsofcatapults/home/how-a-catapult-works-the-basics
https://www.sciencebuddies.org/blog/simple-catapult-science