Materials Required -
balsa wood, thick cardboard, strong glue, dowel, small container, rubber band, 3 metal hooks, drill, wood knife, water paint, foam pieces
Method of Construction -
We cut balsa wood to make a base, 2 side arms and the lever. 2 side supports were cut out of cardboard. We then drilled holes 2 cm apart along the lever and arms. The 2 arms and cardboard supports were glued to the edges of the base. The container was then glued onto one end of the lever. Once all the glue had dried, we were able to attach the lever with the dowel by matching the holes on it and the arms. Next, the hooks were screwed into the base at one end. The rubber band was then attached to the last hole on the lever and pulled down onto one of the hooks. We were then ready to test the catapult.
Our Results -
We dipped some sponge pieces in a tin of paint and placed them in the catapult container one at a time. Next we pulled the lever back and shot the sponge pieces at a target made out of a cardboard box. We were trying to hit the bullseye on the target. It took us 20 shots before we hit it directly on the bullseye. We were also investigating what happened when the lever was connected to the side arms through the holes at the different heights. We found that if you put the lever on the top hole the projectile (sponge) goes the highest and the furthest but if you put it on the lowest hole it doesn't go very high or far at all.
Problems We Discovered -
We found that because our base wood was so thin the metal screws couldn't go into it very securely and they sometimes came out. Our teacher pointed out a few problems that he discovered. The 2 arm pieces of balsa wood were quite wobbly and our piece of dowel was too thin. We really needed to be able to keep the variables more constant. The foam pieces were a bit light and didn't shoot very far so we used pieces of chalk at school. We have thought of some ways of improving our catapult:
- gluing the base onto a thicker piece of wood to make it stronger.
- putting another piece of wood across the top of the 2 arms to stop them moving so much.
- gluing a smaller and deeper container onto the one we have so the projectile wouldn't fall around so much.
We both found the experience a lot of fun. Why not try buiding a better one than ours?