EDIT TO THANK ROADCHOADE FOR CORRECTING MY CALCULATION ERRORS... I fell into a ballistics trap and i have now seen the error of my ways
The experiment design is still sound, and i feel now an even better experiment to demonstrate external ballistics and momentum.
I concur with data monkey
these 8th grade science projects are not a "lets do something cool then just explain it"
they are and examination of the scientific process primarily, and the topic of the project is secondary
the student basically has to start with a question, think of a hypothesis, test the hypothesis by testing variables against the original constant, and then observe the results to determine whether or not the hypothesis was correct or not.
one can't think of a science fair project by saying this would be a cool experiment, you have to come up with a question, then a hypothesis (if i do this then this will happen) then design an experiment to either prove or disprove the hypothesis
ex.
Question: How will changing the weight of a projectile, given a constant muzzle velocity, an initial bore angle parallel to the level surface of the earth, and a constant distance to the target, change the external ballistics of the projectile.
Hypothesis: As I increase the bullet weight, the bullet will fall further from parallel to the initial bore angle faster, due to the increased mass over the constant. Alternatively, If I decrease the projectile weight, the trajectory will remain closer to parallel with the level angle of the bore for a longer time and distance, due to the decreased mass as compared to the constant.
With help from a reloader friend/gunshop with a chrono/etc... develop a load of .38 special from a revolver with (min 4", 6 or 8 would be better) using 158 grain bullet as constant, the loads do not have to be real powerful, but try to develop a load that the velocity at the muzzle can be duplicated using a 130 grain bullet as well as 200 grain bullet. The slower you push them, the more dramatic the results will be.
Experiment: Using vice or clamp of some sort, secure the revolver so that muzzle rise variable is eliminated, as heavier bullets can recoil enough to raise the point of impact. Shoot a 158 grain bullets at a large piece of cardboard aimed (aimed only for the X-axis, the Y-axis, or bore angle, should be 0 degrees or perfectly level with the ground) at a vertical line designated for that particular trial. Mark the hit then repeat for the 130 grain bullet, as well as the 200 grain bullet, being sure to use the same trial line for each series of three bullets. Repeat each trial at least 5 or 10 times...the more trials you have, the more accurate the experiment will be, in order to account for uncontrollable variables, like gunpowder variances.
Ill let you and your son to draw the conclusions, but just remember, control the variables as much as possible. To have a valid argument and hypothesis, you can only change one variable. In this case it's the bullet weight, thusly, the muzzle velocity, initial trajectory angle, barrel length, and recoil-ability, must be controlled and reproduced for every trial.
Use graphs to show the trajectory, and take lots of pictures and use diagrams to show the set up and experiment etc...
I feel like this would be a fun, interesting project, and would be captivating enough for 8th graders, and have enough science and repeatability to wow the judges at higher levels of competition
(I wish i had thought up this experiment when I was in eighth grade, not a senior at the University of Florida :banghead: )
here is a diagram of the proposed target and a diagram of the theoretical trajectories given the variables and constants