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).
The amount of preparation done by the teacher versus the student is dependent on the intended outcome, as well as the individual skill sets of the students involved. For example, if this activity is being used as a tech engineering project the students may spend more dedicated time building the rocket, whereas in a physics class it may serve as a demonstration, completely prepared by the instructor. Serious safety precautions must be taken during this activity and adult supervision is required. Adaptations are shown for all stages of the activity for students with visual impairments. During the building of the rocket WikkiStix® are used, as well as (optional) ring stands, funnel, and braille measuring spoons. A buzzer is attached to the side of the rocket, so as to provide auditory feedback during the launch.
Prior to beginning the activity the instructor should decide upon how many rockets they would like to make. We chose two rockets, so that the students could observe the effect of different quantities of baking soda. Collect that many 2 liter soda bottles, and all other necessary materials. Place a Wikki Stick® or thick piece of tape around the bottle approximately 5 cm from the bottom of the bottle. This will act as a guide for the student as they place the “legs” or “fins” on their rocket. You might also place WikkiStix® vertically down one side of the bottle to indicate where the buzzer and battery holder may be placed and fixed down with tape. Cut several pieces of clear plastic tubing (about 5-10 cm in length) and tape one of the ends shut. These will act as ‘fuel capsules’, and will hold the baking soda long enough for you to step back and reach a safe distance away from the rocket. The tubing should be slightly smaller in diameter than the neck of the 2 liter bottle. It is also recommended that the instructor obtain a plastic sheet or other material to place the rocket on, so as to make clean up easier.
1. Collect a 2 liter bottle (with WikkiStick® placed around circumference of bottle) and 4 craft sticks. Cut about a foot of tape and place sticky side up. Place the four sticks evenly apart along the tape, at even heights.
2. Locate the guide line on the bottle and roll the bottle over the tape, until the entire length of tape with all four legs are attached firmly to the bottle. Stand the bottle up on its legs to test whether it is balanced. If not, check for any legs that may be at slightly different heights, or may not be affixed firmly enough.
3. Place a Velcro dot or piece of double-sided tape on the underside of an electronic buzzer. Attach the buzzer to the bottle near the neck, and add a small piece of tape to the connecting wires. You want the wires to reach down below the buzzer so as to make it easier to connect to the battery. Attach the battery case below the buzzer, as seen in the photo below. Just before launching the rocket, attach the battery and buzzer together by connecting their leads to create a steady sound that should remain audible as the rocket whizzes overhead.
4. Now you are ready to add the vinegar. Attach the neck of the bottle to a ring stand for added support, or have an assistant hold the rocket steady. Place a funnel in the bottle and begin filling with vinegar. Fill about one third of the way, or until it reaches the line you made with the WikkiSticx®. Cork the bottle, or cover it with a cap.
5. Now you are ready to create the fuel capsule. Place the piece of tubing in the grip, or have an assistant hold it steady. Place the funnel in the tubing and pour 2 -3 tablespoons of baking soda into the tube. Place a small piece of tissue into the open end to plug it. The tissue should dissolve when it is dropped in the vinegar, allowing you time to cork the rocket, flip it over, and step away to a safe area. Keep your capsule(s) separate, possibly in a small try so as not to spill the contents.
1. Choose a launch site that is away from school buildings. Place the plastic sheet down if you are concerned with vinegar and baking soda making a mess on the ground. Have students put on safety gear.
2. Connect the leads of the battery and buzzer to create a steady audible tone.
3. Place the rocket so that the nozzle is facing up and uncork the opening. Drop the capsule of baking soda into the rocket and quickly cork the bottle. Give the bottle a shake, flip it upside down, and stand it on its legs. Make sure it’s absolutely balanced (you do not want it to suddenly tip and be facing towards you)!
4. Allow for the chemical reaction to occur and for pressure to build. The rocket should launch after approximately 5-20 seconds of time.
We extended this activity by adding a second rocket, with an equal amount of vinegar, to the demonstration. We used 3-4 tablespoons of baking soda in this second rocket (as opposed to 2 tbsp.) in order to observe whether a greater amount of baking soda would result in a reaction force with a greater magnitude, thus sending the rocket even higher.
As previously mentioned, if this activity were being used in a technology engineering class, students might experiment with different designs, using a variety of body shapes, plugs (rubber stoppers), and capsule designs.
This adapted physical science activity is based on this original rocket design found here at Steve Spangler Science: https://www.stevespanglerscience.com/
Middle School – Forces and Interactions
PS2.A: Forces and Motion
PS2.A: Forces and Motion
By Stu Grove
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