Modified from Rockets: A Teacher's Guide with Activities in Science, Mathematics, and Technology, 1996.
Build and decorate a model rocket using a 35-mm film canister with a fuel mixture of baking soda and vinegar as the rocket's engine. In Part 2, experiment with the effects of different mass and varying fuel mixtures on the rocket's flight.
What's the Point?
- A force must be exerted for a rocket to lift off from a launch pad.
- The greater the mass of the rocket, the greater the amount of thrust needed to launch the rocket.
- Different shapes and sizes of rocket nose cones, body, and fins alter the characteristics of a rocket's flight.
For each child or small group of children:
- Cardstock (8 × 10 sheets)
- Rocket cutout pattern guide
- Plastic 35-mm film canisters (The film canister MUST be one with a cap that fits INSIDE the rim instead of over the outside of the rim.) Some science education stores now sell these, including Science Bob Store, Steve Spangler, Educational Innovations.
- Cellophane tape
- Colored markers
- (optional) Decorative stickers
- Plastic picnic spoons (or a set of measuring spoons)
- Baking soda and vinegar (Alka-Seltzer and water can be substituted)
- Modeling clay or play-doh
- Paper towels
- Eye protection
For the facilitator:
- Print the rocket cut-out pattern onto cardstock for each participant.
- Make an example model rocket and conduct a test launch in advance.
- Gather the materials.
- cardstock with the rocket cut-out pattern
- 35-mm film canisters
- scissors, tape, and rocket-decorating supplies
- Wrap the rocket body section around the film canister so that the lid of the canister can be snapped on and off without interference. Tape the rocket body to the film canister before wrapping it around the canister.
- Tape the outside seam of body cylinder closed. Refer to the illustrated instructions.
- Tape the fins onto the rocket, making sure that they are evenly spaced around the base of the rocket body.
- Roll the nose cone section into a cone the same diameter as the rocket body. Tape the nose cone together, then tape it to the top of the rocket body.
Launching a Model Rocket
- Go to the launch site.
- Choose a launch platform that is outside or in an uncarpeted room with a high ceiling at least 20 feet tall.
- All children other than the child launching his/her rocket should stand at least 10 feet back from the launch area.
- Make sure that the child launching his/her rocket is wearing eye protection.
- Add the fuel.
- Turn the rocket upside down, take off the film canister lid, and place 1 teaspoon of vinegar into the film canister.
- Measure ½ teaspoon of baking soda.
- Pour the baking soda into the film canister.
- Quickly snap on the film canister lid and quickly place the rocket rightside up onto the launch platform. Step back from the launch platform.
- These steps need to be completed very quickly as it only takes a few seconds for sufficient gas pressure to develop to blow the lid off the film canister.
- Watch the launch
- Invite the children count down backward from 10.
- Have the children judge the relative height of each launch by referencing the maximum height to a specific point on a background object.
- After each child has launched his/her rocket, discuss their observations, hypotheses, and conclusions.
- Why did some rockets fly higher than others?
- How is your rocket similar to, and different from, a real rocket?
- What caused the rockets to move?
- What could be changed to make the rockets fly higher?
- What would happen to the rocket's flight if you removed the nose cone and/or the fins?
- What would happen if two similar rocket engines, facing directly opposite each other, were ignited at exactly the same time?
How do Pop-Rockets work?
When vinegar and baking soda are mixed together, carbon dioxide gas is released in a bubbly reaction. The reaction has two steps. In the first, carbonic acid is produced. Because the carbonic acid is very unstable, it breaks down in a second reaction to form water and carbon dioxide.
The release of carbon dioxide provides the thrust of the model rocket engine. The pressure of the gas eventually builds up until the container cannot hold the gas and the pressure is released by forcing the lid off the container. This expulsion of exhaust creates thrust to send the model rocket off the ground.
Part 2: Adjusting Variables
- Add additional mass
- Give each child a piece of modeling clay about an inch square. Have them mold the clay into equal-sized small disks (the same size and thickness as a quarter). This should yield 5 or 6 quarter-sized pieces of clay.
- Carefully take off the nose cone. Place a single quarter-shaped 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.
- Launch the modified rocket
- Follow the same procedure for loading the baking soda and vinegar into the film canister as previously described in steps 5-6.
- Have the children judge the relative height of each launch, and record the height reference point for this launch with this amount of clay.
- Repeat, adding one more piece of clay to the rocket for each launch. Emphasize that they should try to use the same amounts of vinegar and baking soda each time.
- Summarize their experimental results.
- Although their observations are qualitative, the children 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.
- If time permits, vary the rocket fuel mixtures while keeping the weight of their rocket constant.
- Some variables that they might test include using the same amount of vinegar but altering the amount of baking soda (1/8 teaspoon, ½, ¼, 1, 2, etc.); using the same amount of baking soda, but different amounts of vinegar; pouring the vinegar into the canister over the baking soda; or using different strengths of vinegar.
- At some point, adding more baking soda will make no difference.
- Discuss how this model resembles an actual rocket launch, and the limitations of this model.
Facilitator Information about Rockets
There are two main types of rocket engines: liquid-propellant engines and solid-propellant engines.
Propellant for liquid rockets is stored in large tanks. The propellant components of the fuel (for example, hydrogen) and the oxidizer (for example oxygen) are stored in separate tanks. The propellant is pumped into a combustion chamber, where it is mixed and ignited. The propellant burns, creating gases under high temperatures and pressures. The expanding gases escape through the nozzle at the lower end of the rocket. The nozzle has a narrow throat which limits the amount of gas that can escape, causing the gas to accelerate as it leaves the engine. As the exhaust is forced out of the nozzle, it propels the rocket in the opposite direction.
Solid-propellant rocket engines use a dry mixture of fuel and oxidizer. Under normal conditions the propellant does not burn, but it’s ignited at launch, beginning combustion. Like the liquid-propellant engines, combustion of the propellant creates hot, expanding gas that escapes through a nozzle at high pressure, generating thrust.
The combustion of liquid-propellant engines can be controlled more easily than solid propellant, but liquid is heavier and requires more massive rockets and engines. Solid rocket propellants are common for military uses such as missiles and are the most common propellants for model rockets. Liquid-propellant systems are more commonly used by the space industry for human and non-human research and exploration.
When a rocket is being launched, there are two forces acting on it. One is the weight of the rocket, the force generated by the gravitational attraction of Earth on the rocket. The second is thrust, the force that moves the rocket. A rocket launches when the thrust of the engine exceeds the gravitational force keeping the rocket in place. In general, the heavier the rocket, the more thrust needed to get it off the ground.
Once the model rocket is airborne, drag will affect it. Drag is the rocket's resistance to motion, caused by the rocket's movement through air. It depends on several factors, including the density of the air, the shape of the rocket, and the roughness of the rocket's surface. The more resistant to motion a rocket is, the more thrust is needed to propel it. The nose cones of rockets are streamlined to help reduce drag. Once a rocket leaves the atmosphere, it no longer experiences drag.
Once the model rocket has used all of its fuel, it no longer accelerates. However, Earth's gravity continues to act on this rocket to slow it down. If the rocket's speed is slow enough, Earth's gravity eventually will pull it back to Earth. If the rocket's speed exceeds 17,500 miles per hour, it is going fast enough to go into orbit around Earth. If the rocket's speed exceeds 25,000 miles per hour, the rocket is able to escape Earth and explore other regions of our solar system.
Rockets must be stable in flight — they must be able to fly in a smooth, predictable direction. An unstable rocket may tumble or fly in the wrong direction. Fins help stabilize the rocket by streamlining the flow of air and keeping the center of pressure behind the center of mass of the rocket. As rockets have become more advanced, scientists have experimented with fins that they can move during flight to alter the direction of the rocket. Fins only help stabilize a rocket when there is air present. In space, the angle at which exhaust is vented is changed to alter the direction of the rocket.