# Catapults

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• Publicado : 4 de junio de 2011

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Introduction
The objective of this experiment is to explain the basics of horizontal motion using a catapult as a model and to apply the theory in real situations. Horizontal motion is thecombination of two different axes: the x-axis, which has constant speed, and the y-axis, which has constant acceleration and is freely falling. These two motions are independent from each other, so whathappens in one does not affect what occur in the other one. Catapults were invented long time ago when the oldest civilizations (probably the Greeks) used them as weapons against their opponents. Catapultscan be used in horizontal motion, but also in projectile motion. This experiment focuses on horizontal motion because of the type of catapult used.

Content
My team chose this specific experimentbecause it was easy to determine the values and to build. The catapult was made using pieces of wood, elastic bands, little hooks and a 5-gallon-water bottle top. The first time we used it, we had tobuy another elastic band because it broke instantaneously; we also had to use more than one so that the elastic part could work. Then we had a hard time with the base (the part where the projectile isplaced to be thrown) because it turned every time we used it.

Experiment development
Finally, when we had no problem with the catapult, we applied our knowledge to develop the experiment: on astone slide in a park near Jaqui’s house, we threw some rocks about the same sizes and shapes. The slide was approximately 1.8m high (y). We took the air resistance as neglected, so the gravityacceleration was 9.8m/s2 (g). We think this experiment is accurate because the measurements were taken using specialized devices for this kind of situations. By the way, that day was too sunny.

DataExperiment | Time (t) | Distance (x) |
1 | 0.6s | 4.00m |
2 | 0.4s | 2.61m |
3 | 0.6s | 3.47m |
4 | 0.4s | 2.56m |

Analysis and results
Vx=xt Vfy=gt V=Vx2+Vy2
Experiment | Speed (Vx) |...