The Physics

• A trebuchet is a type of catapult that utilizes the mechanical energy of falling counterweights to launch a projectile. 

Energy

• Mechanical Energy is the sum of Kinetic (the energy of moving objects) and Potential Energy (the energy of an object in relation to other forces acting on it).

• The Trebuchet System has potential energy as the counterweights are held in the air before release.  It has kinetic energy when the weights are falling and launching the arm. 

• The Law of Conservation of Energy states that energy is conserved, so when potential energy goes up, kinetic energy goes down, and as kinetic energy goes up, potential energy goes down.  Because of this rule, the sum of potential and kinetic energy in the system is always equal. 

Energy can change forms

 

































Force

• Gravity works on the counterweights and is what ultimately pulls them down and swings the arm up. 

• The normal force is the actual weight of the trebuchet pushing down on the ground, and due to Newton's 3rd Law of Motion, the ground exerts an equal and opposite force back on the trebuchet.

• Newton's 2nd Law of Motion states that acceleration of the trebuchet is directly proportional and in the same direction as the net force, and is inversely proportional to the mass.                        

1. F=ma
2. The heavier the weights, the greater the force applied to the trebuchet. 

• The counterweights, sling, arm, base, and axle of the trebuchet are all exerting forces on each other

• Centripetal force acts on the sling as it completes an arc around the trebuchet before it is launched, and as the arm rotates around the base after the weights drop

• Because of this added force, the acceleration of the trebuchet increases, and since the acceleration increases, while the mass stays basically the same, the net force is increased





Projectile Motion

• Projectile Motion is the ascent and descent of an object

• In the case of the trebuchet, the object will travel in a parabolic shape when it is releases from the throwing arm


• The angle that the object should be released at to get the greatest distance is 45 degrees from the normal.  This is called the critical angle, and provides for the greatest altitude while also getting the greatest distance.

       

• d=Vi+(1/2)*a*t

Log of Meeting Dates

First Meeting: May 4th, 11:24 am - 4:45 pm

• Built the base of the trebuchet
• Drilled holes in the supporting arms and nailed them to the base
• Cut out the throwing arm and drilled a hole through the center
• found a thin sheet of wood and put it over the base
• Cut out a piece of an old basketball hoop and used it as the axle
• Attached arm to axle and supporting arms
• Members present:
• John, Hunter, Patrick    

Second Meeting: May 12th, 1:33 pm - 3:00 pm

• Made the sling out of some super absorbent material
• Built trigger mechanism
• Worked on Physics part of the presentation
• Members Present: 
• John, Hunter, Patrick  

 Third Meeting: May 18th, 10:42 am - 5:36 pm 

• Threw away old sling and made a new one out of flexible cloth   
•  Figured out how long the strings of the sling and the nail at the top of the arm had to be to launch the projectile the farthest by doing trial after trial... after trial... after trial... after trial
•  Painted and decorated the trebuchet
• Compiled all pictures and videos that we had and put them into Blogger
• Members Present:
• John, Patrick





Trial One

• Full-sized sling
• Long strings
• Sides of sling were not stapled yet
• Longer nail on top of throwing arm where the sling attaches
• Ball flew out of sling backwards, which meant that it was releasing way too early

Trial Two

• Minor adjustments
• Made strings a little shorter, but still too long
• Cut the sling down to half of its original size
• Ball slipped out of the sling before it even made it in the air
• We decided to move the trebuchet into the shade facing the street because at that point we were pretty sure that nothing would launch far enough to hit anything

Trial Three

• Final Launch
• Sling hangs down to right above the axle of the throwing arm when arm is up
• Changed the sling from lying down horizontally to lying down vertically
• Ball was released at just the right time and flew across the street, which was over 25 feet

 The Beginning

Power Tools

Piece of an Old Basketball Hoop

Manually Cutting Metal

Drilling Holes in the Wood for the Axle

Hunter Trying to Look Like He is Doing Something

Nailing Supports In

First Prototype...

...Didn't Work Very Well

New and Improved Trebuchet With Salt Bag to Weigh it Down

Sling Made of Cloth

Concrete Weights Clamped to Arm With Metal Rods

Bent Nail for The Trigger Mechanism

Washer for Part of the Trigger Mechanism Attached to Base

Trigger Set up to be Launched

Final Product (Minus Paint)