Physics Behind the Trebuchet: Energy

ENERGY:
Before launch, the trebuchet arm has Potential Energy (PE). After the trebuchet arm is released, it has Kinetic Energy(KE), and the arm and trebuchet continue to have Kinetic Energy even after the water balloon has been released. The water balloon has Kinetic Energy as soon as the arm starts moving, and continues to have Kinetic Energy all the way through its flight until it hits the ground. Because Kinetic Energy's equation is KE=0.5m(v)^2, an increase of the velocity would increase the Kinetic Energy, and increase the range. The velocity can be increased by increasing the length of the arm and sling. The range can also be increased by adding more weight, because with a larger weight, the arm will have a greater Potential Energy, and because of the Law of Conservation of Energy, the arm will also have a greater Kinetic Energy, which leads to a greater range.

Physics Behind the Trebuchet: Projectile Motion

PROJECTILE MOTION:
Vix = vcos(theta): it is the horizontal component of the angle of release.

Viy = vsin(theta): it is the vertical component of the angle of release.
y = the maximum height that the water balloon reaches during its flight. At this point the vertical velocity is zero.
x = the total distance of the water balloon's motion.

To increase the range and maximum height (x and y), the velocity must be increased by decreasing the angle of the release mechanism nail.

Log of Meeting Dates

April 17^th: Created a blog and started research about the trebuchet’s history.

May 8^th: Researched Trebuchet designs and found a simple design, but had to scale down the measurements by 2/3rds to fit the size requirements.

May 9^th: Cut the required pieces and drilled the holes, assembled the trebuchet frame.

May 10^th: Attached the sling and the weights, experimented with amount of weight and the angle of the nail to release the sling.

May 11^th: Changed the arm into a longer piece of wood to maximize the throwing distance, and attached the trigger mechanism.

May 12^th: Worked on the steps for building the trebuchet with pictures.

May 15^th: Completed the Process of Design and Construction started the previous meeting and started working on the physics concepts behind the trebuchet.

May 17^th: Finished describing the physics behind the on the Trebuchet.

May 18^th: Tested the trebuchet again. Painted the trebuchet.

May 19^th: Edited videos, finished the steps and materials list. Posted the materials list, the trebuchet building steps, and the 3 trial run videos with the flow chart. Cited sources for the Trebuchet History. Posted the Trebuchet History.

May 20^th: Practiced releasing the trebuchet in preparation for Friday.

Physics Behind the Trebuchet: Forces

FORCES:

Because the sling side of the lever arm is longer than the counterweight side, the sling side has to move faster than the counterweight side of the lever arm when the trigger is released. The sling works because of tension. At the beginning, both the fixed and sliding rope of the sling have tension, but at some point in its path, the sliding rope decreases in tension and continues to decrease until the rope slides off. The sling itself experiences centripetal acceleration, and it has to move faster than the sling side of the arm, therefore much faster than the counterweight side of the lever arm, when the trigger is released. Increasing the length of the arm and the length of the sling would increase the trebuchet's range.

Centripetal Force(Fc): This is the force acting on the sling that causes it to move in a circular manner until released.
Acceleration(a): As gravity affects the lower side of the arm, the upper side experience acceleration.
Gravity: Gravity is what pulls the counterweight down, and thus moves the arm.
Normal Force(Fn): The force that the ground exerts upon the trebuchet.

"Trebuchet Physics." Trebuchet Physics. Real World Physics Problems, n.d. Web. 20 May 2014. <http://www.real-world-physics-problems.com/trebuchet-physics.html>.  

The History of the Trebuchet

The trebuchet is considered to be “one of the most fearsome weapons of medieval times.”

“The word 'Trebuchet' is derived from the Old French word 'Trebucher,' meaning to throw over.”

The trebuchet was used by the Mongols at the Siege of Caffa in one of the first cases of Biological Warfare.

The Trebuchet originated in China in 300BC. It was later used in Medieval Europe around 500AD. The French were the first Europeans to use the trebuchet, and changed it to rely on a counterweight at the short end of the lever, instead of manpower. In 1216, the trebuchet was used by France’s Louis the Dauphin during the Siege of Dover in England. This exposure to the trebuchet caused King Edward I of England to order the building of an English version of the trebuchet, and this design--called the Warwolf--is considered “the most powerful and most famous of the trebuchet.”

"Medieval Arms Race." NOVA Online. WGBH Educational Foundation, Nov. 2000. Web. 17 Apr. 2014. <http://www.pbs.org/wgbh/nova/lostempires/trebuchet/race.html>.

"Trebuchet." Trebuchet. Lords and Ladies. Web. 17 Apr. 2014. <http://www.lordsandladies.org/trebuchet.htm>.

Trebuchet Trial Runs

Trial 1:

Trial 2:

Trial 3:

10+1 Steps to Building a Trebuchet

Step 1: Cut all of the wood pieces into the correct sizes. 

Step 2: Drill the wood pieces together to form the rectangular base.

Step 3: Drill the holes for the dowel in the side pieces and the lever arm.

Step 4: Drill the side pieces onto the base and then attach the triangles for extra support.

Step 5: Slide the dowel through the side arms and the lever arm.

Step 6: Create a sling attached to the lever arm on one end, with a loop on the other end to connect to the release nail.

Step 7: Attach the weights to the short side of the lever arm, and attach the sling to the other side. Bend the nail to a desired angle and then test its position through trial and error to determine the best angle for your sling's length.

Step 8: Attach a flat board to smooth the sling’s flight.

Step 9: Test your catapult! You may have to make minor adjustments to the angle of the nail, the length of the sling, or the amount of weight attached to the lever arm.

Step 10: Create a trigger mechanism for your trebuchet using a piece of nylon rope, half of a shish kabob skewer (or some other item that can be used as a pin) and eye-hole screws.

You’re DONE! :)

Optional final step: Paint your trebuchet!