Fire Away!

Fire Away

Description of Design

Our catapult design was simple. We started with a 4x6 flate piece of wood which we used for the base. The flat piece of wood allowed the catapult to sit flat on the concrete without any trouble. From there, we drilled in one tall skinny piece of wood on each side of the trebuchet for the legs. The legs held a metal bar that went through the top of the legs. We drilled two holes directly across from one another on each leg and we put the metal bar through those holes. Next, we took a long skinny piece of wood and drilled a hole through it and placed it on the metal bar. This was the arm of the catapult. This was what threw the ball into the air. Next we hammered a finishing nail into the end of the arm. This is where we hung the clay ball and string so that when we let go of the arm the ball was launched off the finishing nail. Next we also have a nail going horizontally through the other side of the arm. This is where we put the rubber bands that put force on the arm allowing it to launch the ball. We had 5 rubber bands on each side of the nail. Having rubber bands on each side allowed us to have more force without the arm snapping. Those rubber bands are then connected to the nail that we hammered into the base of the catapult. Before they connect to the base of the catapult, they are braided so that they have extra force on the arm and then are connected to the nail on the base.

5 modifications made

Location of Rubber Bands on Base

At the base of the Catapult we had nails about 6 cm away from each other and we tested each location to see which allowed the rubber bands to have more force so that the clay ball could go as far as possible. We ended up with having the rubber bands go from the back to the front which allowed the rubber bands to have a great amount of force which launched the clay ball pretty far.

The way the clay ball was launched

At the beginning of the project when we first built our catapult we had a nail at the end of our arm to launch the clay ball into the air. The nail we used had a head that was to big so the string was getting stuck on the nail and just being shot straight up into the air. The ball was being shot straight up and coming back down and landing at around 10 meters. At that time we didn’t realize that the nail was the problem so we switched to a measuring spoon. This worked well the first few times but after a couple tries we realized that it wasn’t working. The ball was only going about 10-15 meters still. We then switched back to a nail but this time we used a nail with a smaller head. This allowed the clay ball to be launched around 35-45 meters each time which was much further than before.

Amount of Rubber Bands

When we first started the project we used around 4-8 rubber bands. This worked well until we realized they were constantly being stretched out and loosing there stretch. So we then added around 15 more rubber bands. At this point there was so many rubber bands the ball just got launched straight into the ground. We then decided to put a screw threw the arm and we had around 4-6 rubber bands on each side. This was a good amount because it wasn’t to loose to the point where the ball didn’t have enough tail wind, but it wasn’t tight enough to launch the ball straight into the ground.

Size of projectile

For our projectile we used a clay ball. Originally we thought that a bigger ball would fly further. After many trials we realized that it had to much weight and was not being launched as far as possible. We then tried to use a smaller ball. This worked much better than the bigger, heavier ball. The ball was being launched at least 5 meters further than the bigger heavier ball.

Length of Arm

At first, we had a very long arm. We thought that this would allow the ball to be launched as far as possible, that was very inaccurate. A longer arm resulted in loss of energy. We never actually realized that until our arm snapped in half and we were forced to use a shorter arm. When we started using the shorter arm we realized that our arm had a lot more energy than before when we were using the long arm.

Claim Evidence Analysis Poster

Technical Specifications

Mass of Projectile; 0.013kg

Time in Air: 1.9s

Horizontal Distance: 30m

Vertical Distance: 17.7m

1/2agt^2

1/2(9.8m/s^2)(1.9s)

17.7m

Velocity Horizontal: 15.8 m/s

Vh=dh/t

Vh=30m/1.9s

Vh= 15.8 m/s

Velocity Verticle= 9.3 m/s

Vv= 1/2agt

Vv= 1/2(9.8 m/s^2)(1.9s)

Vv= 9.3 m/s

Total Velocity: 18.3 m/s

Vtotal= a^2+b^2=c^2

Vtotal= (15.8 m/s)^2 + (9.3 m/s)^2= Vtotal^2

Vtotal=18.3 m/s

Release Angle:

Spring Constant;

Initial Spring Potential Energyt: 37J

PEspring= 1/2 kx^2

PEspring= 1/2(350 N/m)(1.9s)^2

PEspring=37J

Kinetic Energy: 350 N/M

k= F/d(20)

k= 4.9N/.28m(20)

k=17.5 N/m(20)

k= 350 N/m

Percent of Energy Converted: 6%

PEconverted= KE/PE

PEconverted=2.2J/37J

PEconverted=6%