Fire Away

Aidan Whitmore

Mr. Williams

Period 1

10 November 2022

Proof of Efficacy Document

Our Design

On November 3rd, we were given the task to create a trebuchet or a catapult that would have the end result of launching a clay ball as far as you can. A trebuchet is a specific version of the catapult that uses a counterweight to create the force to fling an object while a catapult is a forked stick with an elastic band kind of like a slingshot. Our trebuchet was 1m high at its peak with a 9in axle, 1 ft arm, and a 1ft by 2ft base.

Selling Points/Modifications

Some selling points/modifications of our trebuchet is our arm, which we had to tweak a lot to get the right mass, and size. We drilled countless holes into the side to lose weight along with cutting the edges down to just the right size. This made the arm super light to be able to reach a higher velocity to launch our projectile. Another thing we tested a lot was the size of our projectile, and we found that the lighter the ball the farther it went till a certain point. Past 0.05 g, the ball was too light to have a good trajectory to travel far. Another modification we made was the string length which was the string that connected the projectile to our arm. We found that a 4-5 inch string was just perfect, as if the string was too short, that angle of release would be too high launching the ball straight up. But if the string was too long, the angle of release was too small, launching it into the ground. We also tested a couple other designs on our trebuchet, but a couple more modifications that we found that increased the distance of our projectile alot was when we changed the origin of our rubberbands. We found that when we had one end of the rubberband right below the arm, it worked the best because we were able to stretch the rubber bands just the perfect amount so that they didn't break, but weren't too short that the projectile wouldnt travel very far. A few more modifications we made was how many rubber bands we used on our trebuchet. We found that 2-3 rubber bands worked the best because there were just enough to give us the right resistance and potential energy flinging our object. Any more would have been too hard to pull back and they would break, and any less wouldn't have enough resistance resulting in the projectile to not travel too far.

One more modification we made to our trebuchet was testing the different sizes of our base. This didn't have too much of a difference to the distance our projectile traveled but it was a lot more sturdy and took some of the flexing and friction from the legs and put it into the ball so there was a little improvement there.

Claim, Evidence, Reasoning Poster Slides

Our Claim: There is a happy medium when it comes to the length of the string that attaches the projectile to the arm and it is around 4-5 inches.

We found this out through many tests, and after the tests we got some interesting results from our machine. We found that too long of a string would result in the angle of release of the projectile would be too small, fling the clay ball straight into the ground. But if the string was too short, the angle of release would be too great resulting in the clay ball flinging straight up into the sky. So we found a happy medium where it would have just the right angle of release with enough distance vertical along with distance horizontal.

Content

Mass of Projectile: 0.07g

This is the weight of our projectile(Clay Ball).

Horizontal Distance: 17m

This was the distance our projectile was flung.

Time in Air: 1.3s

This was the whole time our projectile was in the air

Vertical Distance: 2m

This was the distance our projectile travels upwards (Y Axis).

Horizontal Velocity: 13m/s

This was the speed our projectile traveled on the horizontal plane (X Axis).

Vertical Velocity: 6.37m/s

This is the velocity of the clay ball going up (Y axis).

Total Velocity: 14.53m/s

This is the speed of the ball while it is in the air.

Angle of Release: 26 degrees

This is the angle at which our clay ball is released from the arm.

Spring Constant: 106n/m

This is the amount of force the rubber bands have on the arm.

Initial Spring Potential Energy:11.7J

This is the force of the rubber bands on the arm before it is released(Potential Energy).

Kinetic Energy of the Ball:0.0738J

This is the energy the ball has when it is released from the arm.

Percent Energy Converted:63%

This is the amount of energy that has been converted from Potential Energy to Kinetic Energy resulting in the clay balls % of KE which is the actual amount of energy that ball has as its been released.