"We are studying acceleration, and will eventually segway into force, impulse, and several other related items. During this unit, I introduce rocketry to make the material more relative. The kids start out by constructing air-powered rockets (we use an old "stomper rocket" setup I bought way-back-when) without knowing much at all about rocket "stability." I encourage them to experiment, and then we launch. It's usually quite comical, as some of the rockets will barely make it off the launch pad. We then go back and look through center of gravity (weight distribution) and center of pressure and how it relates to the stability of rocket flight.
After that, the kids are to make a near-identical rocket which is powered by solid rocket propellant (seen in these pictures) Their design is to fly as high and as straight as possible.
Next, we'll be making much larger (about 30 times heavier) rockets, which will carry an egg as high as possible into the air and land it safely. They'll need to know everything they've learned with the mini-rockets and translate that into an effective flying machine. The kids typically "bat" about .700 on completely successful missions."