Early rockets had a number of stages which gave them boost. The final stage was the rocket being brought back to Earth without power, but the descent was slowed by parachutes.
Your task:
Make and attach a parachute to slow the descent of your rocket.
Compare the time it takes to fall with the parachute with the time it takes to descend without the parachute.
Run a competition to design the best parachute. Decide between your groups how you will measure the “best”.
NB: It is difficult to design a release mechanism for a parachute attached to the rocket, so parachutes can be tested without launching the rocket by dropping them from a height.