2010 Coaches Institute Presentation

NC Science 

Olympiad 

Coaches Institute 

2010

Storm The Castle 

Division B & C

Storm the Castle 

• Prior to the Tournament, Teams will design, 

construct, and calibrate a device that uses 

only the energy of a falling counterweight to 

launch a projectile as far and accurately as 

possible.

• Read the rules 

• Discuss the rules 

• Read the rules 

Rules 

• Have the students copy the rules 

• Read the rules again 

• Highlight the rules 

• Understand the rules

Rules 

Event Parameters 

• Team size, Max of two (2) 

• Must wear eye protection. (ANSI Z87+) 

• Impound event (What does this mean) 

• The launch device, graphs, and all materials 

teams will use must be impounded (checked in at 

the event) prior to the competition.

Design 

Construction 

• Size: everything must fit inside a cube 

(when in the Ready to Fire Position) 

• Division B – 75cm cube 

• Division C – 75cm cube (NC Only)

Construct 

• Floating Arm Trebuchet 

• Recently, a new type of trebuchet has been 

devised. This modern version of the trebuchet 

uses the energy more efficiently, so the range is 

greater compared to a hinged counterweight 

trebuchet. A wheel is fixed to the arm, so that it 

can roll horizontally during launch. The 

counterweight is constrained to a vertical motion.

Construct 

• Floating Arm Trebuchet 

• http://www.youtube.com/watchv=SnpYvpqnNpI

Design 

Construction 

• Triggering device is not part of the device: 

• It may be Battery 

• It may not be radio controlled 

• It may not pose a danger 

• It must extend out of the launch area

• Trigger 

Construction 

• This can be simple or complex 

Arrow 

Release 

Pelican 

Hook 

Panic 

Snap

• Trigger 

Construction 

• You can use eye hooks and a cotter pin 

• Use a strong cord to pull the pin

Design 

Construction 

• Construct the device to accommodate the 

counterweight and the projectiles. 

• No modification of items provided is allowed

Design 

Construction 

• The Counterweight 

• The counterweight will be a 1 to 3 kg mass 

with a hook on top. 

• The hook and the counterweight will fit inside a 

15 cm cube 

• If the hook is used to attach the counterweight, 

the eye must be 9 mm in diameter and no more 

than 6.5 mm thick.

Design 

Construction 

• The Projectile 

• Projectiles will have a mass of 20 – 60 

grams and will be approximately spherical 

with a diameter not exceeding 6 cm.

Projectiles 

• Racquetballs 

• Ping-pong balls 

• Practice Golf Balls

Launch 

• The device, without the counterweight and 

projectile, must not contribute energy to the 

launch. 

• Example: the launch arm must not make a 

launch motion when released from any position 

before the point where the projectile is released.

Catapult Science 

• Math behind the event: 

• www. open2. 

net/diyscience/mangonel/catapult_downloa 

d.pdf


• We must calculate the Force (N) exerted 

by the throwing arm. 

• To do this we need to know the velocity at take 

off calculated in meters per second (m/s) 

• We also must work out how fast the arm 

accelerates. Acceleration describes changes in 

velocity (m/s 2 ). 

• The force comes from the counterweight 

attached to the arm.


• If we know how long it takes to go from 

take off to landing we know it takes gravity 

X seconds to slow from take off speed to 0. 

• Gravity will accelerate any object at 9.8 

meters per second per second. 

• Now we want to figure the Vertical Velocity.

• Vertical Velocity 


• Vv = The final component of velocity in the 

vertical direction = 0 

• Uv=The initial component of velocity in the 

vertical direction= (This is what we are looking 

for) 

• Av=The component of acceleration in the verticle 

direction (-gravity) 

• T = time taken

• So our formula is: 

• Vv = Uv + AvT 


• We know Vv is 0, we are going to assume the 

time (T) is 1.6 seconds 

• Therefore: 0 = Uv + (9.8 X 1.6) solve this 

equation and we have 

• Uv = 15.7 meters/second This is our Vertical 

Velocity we will use it again later.


• Ok, so the projectile does not just go up and 

down. 

• We must look at Horizontal Velocity 

• There is a component of velocity Vx in the horizontal 

direction. 

• This is because they take off at angle theta (Θ) not 

vertically 

• Since Vy and Vx can be treated as vector quantities the 

velocity of take off can be calculated from trigonometry.

Catapult Science


• Vt = Velocity (this is what we are looking 

for) It will be the hypotenuse of this triangle. 

• Vy = Vertical Velocity (15.7 m/s) 

• sin = sine – ratio of the height to the 

hypotenuse. 

• Θ = theta – symbol to describe how big the 

angle is in degrees.

• So our formula is: 

• Vt = Vy /sin Θ 


• We need to know what the angle is 

• The distance the projectile travels depends upon 

the point it leaves the arm. 

• If the angle of trajectory is Θ to horizontal then 

the projectile travels 90 – Θ when being thrown.


• The circumference of a circle is 2pr 

• In our case, r is the length of the throwing arm. 

We will estimate 50 cm. 

• So if the arm traveled a full circle it would travel 

(2 X 22/7 X 50)cm or 314.3 cm 

• So 90 – Θ means our arm moves 314.3(90- 

Θ)/360 cm. (assume 45) 

• The arm must travel 39.3 cm.


• The load needs to leave the arm before it 

reaches 90 or there is no vertical velocity. 

(the force of the arm drops off) You 

probably will max out at 70. 

• We used 45. We will work from here. 

• So Velocity V is 15.7 / sin45 = 22.2 m/s


• We now know how much the arm accelerates with 

a final velocity Vf = 22.2 m/s. We will use this to 

calculate the forces. 

• V 2 = U 2 + 2as 

• V = final velocity (22.2) 

• U = initial velocity (0) 

• a = acceleration (what we are solving for) 

• s = speed assuming constant acceleration over the 

distance moved we calculated the distance moved as 

314.3 X 45 / 360 = (39.3 cm)


• V 2 = U 2 + 2as 

• 22.2 2 = 0 + 2 X a X 39.3 

• a = 22.2 2 / 78.6 

• a = 6.27 m/s 2

• To work out the forces we will use 

Newton’s First Law. 

• F = ma 


• F stands for the net force 

• m is the mass of the projectile 

• a is acceleration

• If the mass of a racquet ball is 39.7 grams 

• And our acceleration is 6.27 m/s 2 

• F = 39.7 X 6.27 


• F=.2489 Newtons (Km/s 2 ) 

• If you use this much force and the ball 

stays in the air 1.6 seconds the ball should 

travel over 35 meters (115 feet).

• The launch area 

is a 2m X 2m 

square. The 

device can not be 

attached to the 

floor. 

Launch Area

• The target will be 

an open toped 

container with a 

minimum 

dimension of 20 

cm X 20 cm X 20 

cm. 

Target Area

Scoring 

• The winner will be the team with the highest Final 

Score (FS). 

• FS = Sum of 2 best Launch Scores (LS) + Graph 

Score (GS) – Penalties 

• Each team gets three launches. 

• To get the score you use the formula: 

• LS = (TD – A) + B 

• LS = Launch Score 

• TD = Target Distance 

• A = Accuracy Score 

• B = Bonus Score

• Launch Score (LS) 

Scoring 

• To get the launch score you use the formula: 

• LS = (TD – A) + B 

• LS = Launch Score 

• TD = Target Distance 

• A = Accuracy Score 

• B = Bonus Score

• Graph Score (GS) 

Scoring 

• To get the graph score (possible 12 points): 

Partial credit may be given. 

• Labeled with school and students (2) 

• Title of graph and X-Y axis (2) 

• Units and axis increments (2) 

• 1 point for each graph (up to 5) 

• 1 point for and example calculation page

• Final Score (FS). 

Scoring 

• FS = Sum of 2 best Launch Scores (LS) + 

Graph Score (GS) – Penalties 

• FS = LS1 + LS2 + GS - Penalties

Scoring 

• Teams will be ranked in tiers based upon; 

• Teams with no violations. (Tier 1) 

• Teams with Competition violations (Tier 2) 

• Teams with Competition and construction violations or 

missed impound. (Tier 3) 

• Tiebreakers are: 

• 1 st Best launch score. 

• 2 nd Second best launch score. 

• 3 rd Third best launch score.

Penalties 

• Ouch! 

• A 3 point penalty will be added each time any of 

the following occurs: 

• Not wearing eye protection 

• Is in the launch area (when a launch occurs) 

• Device goes through an intentional launch motion 

• Does not give a warning prior to launch (Fire in the 

Hole!!!!!) 

• Any part of the device is outside the launch area.

Collect Data 

• The purpose of data collection is to provide 

students with an understanding of test and result. 

• Determine what data you should collect 

• The mass of various projectiles or counterweights verses 

distance. 

• (if you use hand drawn graphs they must be on graph paper) 

• Two copies of each 

• Marked to identify the team and school

• Measure carefully 

Construction 

• Use smooth action on the moving parts. 

• Attach your counterweight for force 

securely. 

• Weight is not an issue. 

• Metal angles will work in many cases.

Construction 

• Make sure your boards and angles are square 

and tight. 

• Be sure the projectile holder does not restrict the 

release of the projectile. 

• Use plywood for stability 

• Use solid construction with screws and or nails 

•Hands on Review of 

Catapults.

Instructor 

• Jim Roberts 

• roberts@campbell.edu 

• Worked with Science Olympiad since 1998.

2010 Coaches Institute Presentation

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