This activity is a fantastic, and flexible, demonstration of Newton’s Third Law in action. Additionally, it may be used to demonstrate an acid/base chemical reaction. Or it may become a great tech. engineering project, in which the students create rocket designs and test the effects of different variables on the performance of the rocket’s flight path. For our purposes, we focused on Newton’s Third Law and the concept of momentum as explanation for how rockets are able to launch into the atmosphere and travel through the vacuum of space. The key terms for the lesson are:
Newton’s Third Law of Motion - For every action there is an equal and opposite reaction (equal in magnitude, but opposite in direction).
Momentum – Inertia in motion. It is the product of an object’s mass and velocity.
Pressure – Force per unit of area.
In this experiment, the chemical reaction between baking soda and vinegar releases CO2 gas, which we trap in the body of the rocket by placing a cork in the nozzle. An excessive amount of pressure is built up until the force is great enough to eject the cork, expelling the gases and remaining liquid downward. This causes enough thrust to launch the rocket upwards into the air! This is a demonstration of a pair of action/reaction forces at work. The action of the push downward by the gases and liquid creates an upward reaction of equal strength but opposite in direction. The reason these forces don't cancel each other out is because they are acting on different objects (the rocket pushes the gases, the gases push the rocket). In a real NASA spaceship, the rocket is fueled by 'propellants' which when mixed together ignite explosions that form gases. The rocket is pushing on the gases, instead of air molecules (of which there are obviously none).