This is one of the better water balloon launcher videos. If you watch close (right at the start of the 26th second) you can see the water balloon (blue) as it comes out of the launcher. This is a lab that my physics students (all seniors) do to calculate the angle of launch of a projectile. Teaching and doing science can be a lot of fun. If you measure the time that it takes the balloon to travel and the distance it travelled horizontally you can calculate the horizontal speed (s=d/t). Assuming that air resistance is negligible and that the balloon reached the peak of its trajecory at the half-way point (in time) then the maximum height can be calculated using the free-fall formula (d=1/2*g*t^2). From there the average vertical speed can be calculated (s=d/t, using 1/2 of the total time). At this point trigonometry can be used to calculate the angle of launch (and Pythagorean's theorem can be used to calculate the average resultant speed).