Heavy Rockets
Overview
Challenges of Launching Heavy Rockets — Children can discover more about the physical principles of rocket propulsion and flight. In Part 2, children incrementally add more mass to their rockets to determine how this change affects the maximum height of their rocket's flight. They are also given the opportunity to explore the effects of different vinegarbaking soda fuel mixtures on the flight of their rocket.
What's the Point?

A force must be exerted for a rocket to lift off from a launch pad.

The motion of the rocket is equal to, and in the opposite direction of, the thrust of the rocket's engine.

The greater the mass of the rocket, the greater the amount of thrust needed to launch the rocket.

Given a fixed amount of thrust, the distance a rocket travels decreases at its mass increases.
Materials

Modeling clay

Blackboard or chart paper for recording flight results
Activity
11. Give each child a piece of modeling clay about an inch square. Have them make smaller pieces of the clay into flat disks the same size and thickness as a quarter.
This should yield 5 or 6 quartersized pieces of clay. Emphasize that they should make each piece as equal in mass as possible.
12. Carefully take off the nose cone. Place a quartershaped piece of clay inside the rocket body, on top of the film canister. Tape the nose cone back onto the rocket.
Ask the children to predict how the weight of the clay will affect the flight of their rocket.
13. Follow the same procedure for loading the baking soda and vinegar into the film canister as previously described in steps 7–9 (see Rocket Launch).
Have the children judge the relative height of each launch. Have them write down the height reference point for this launch with this amount of clay.
14. Repeat steps 12 and 13 above, each time adding one more piece of clay to the rocket.
Emphasize that they should try to use the same amounts of vinegar and baking soda each time.
15. Ask the children to summarize their experimental results.
Although their observations are qualitative, they should see a pattern of decreasing launch height as more and more mass is added to the rocket.
Ask them to explain why this is the case — given a fixed amount of thrust, the distance that a rocket travels decreases as its mass increases.
Ask the children to think of ways, given the same fuel ingredients, to increase the amount of thrust from their film canister rocket motors. They may suggest adding more vinegar and baking soda to the film canister, or different amounts of one of these two ingredients.
16. If time permits, challenge the children to consider altering and testing rocket fuel mixtures while keeping the weight of their rocket constant.
Some variables that they might test include (1) using the same amount of vinegar but altering the amount of baking soda (1/8 teaspoon, 1/4, 1/2, 1, 2, etc.); (2) using the same amount of baking soda, but different amounts of vinegar; (3) pouring the vinegar into the canister over the baking soda; or (4) using different strengths of vinegar.
At some point, adding more baking soda will make no difference. Once the acidbase reaction has produced sufficient gas to pop the top, any further gas production will not contribute to the rocket's motion because the amount of pressure (thrust) needed to pop the top is constant. By starting below the optimal amount of baking soda, children will see an increase in distance traveled as they approach the optimal mix. Once they exceed the optimal mix, they will see no increase in distance traveled.
May 27, 2009