What you'll learn:
How rockets fly and engineering principles
Testing can help you determine what design parameters will lead to the best flights.
Soda bottle rockets are a fun way to stave off the summer heat. Kids will get to engineer their water rocket and watch it blast off, and parents or teachers can add in little challenges to introdeuce engineering and design as well as measurement and decision making.
Once you have your water rocket launcher you only need a recycled 2L bottle, some materials to make fins and cones out of, and plenty of time to launch. As the rockets launch they will spray out water creating a unique and exciting sprinkler to help keep you cool too!
How to make a soda bottle rocket
Making a soda bottle rocket is fairly simple, you need a water rocket launcher that fits a 2L bottleneck, a bottle with a 2L bottleneck, time, and a few recycled materials.
You can either make or buy your water rocket launcher. We followed this set of water rocket instructions to make a launcher – we skipped the O-ring seat step as we couldn’t find the right brass fittings. In the end, it cost us about $25 in materials and a few hours over multiple days worth of time. We also purchased a water rocket launcher online for something in the ballpark of $25 and all I had to do when it arrived was twist two parts together.
Overall, to be honest, unless you are looking for a weekend project with your kids, I would just go ahead and purchase one premade. We used the purchased launcher in our ‘Fizz Boom Pop’ BPAstroKIDS show where we launched a ton of water rockets over and over again. The launcher held up fine and we had no issues (we are definitely upwards of 100 water rocket launches on that system).
Once you have a water rocket launcher, you are ready to design your soda bottle rocket!
1. Pick your bottle
Most 2L will work with your 1/2″ PVC water rocket launcher setup (made or purchased). With that said, some soda bottles work better than others.
We started off with 2L bottles and found that the curvy Coke and Diet Coke bottles seemed to get a better seal than the generic Safeway brand of 2L bottles (like those that sell Refreshe water). This isn’t a huge issue, it just means that you can pump the Coke bottles to a high pressure while leaking less water. A higher pressure means that there will be more force pushing the water out of the soda bottle, thrusting it higher into the air.
We also tried the smaller bottles that still have a 2L bottleneck, like the 1L Refreshe bottles and the small green plastic Perrier bottles. We found that as long as there is a good seal and the bottle is tall enough to reach the zip tie bottle bracket you are good to launch. We did notice that it was easier to get these smaller bottles to fly high. This was partly because the smaller bottle meant less of a cross section and less weight allowing the pressure on the water to go farther. Another reason is it is a lot faster to pump up the smaller bottles. Less volume means less gas to pressurize, and the smaller bottles only take 3-4 pumps on the bike pump to get them flying high!
2. Choose a water rocket challenge
The water rocket launchers are a ton of fun to play with – you can harness this activity to teach science through a few challenges, pick the right one for you for the day!
- Create the best fins and nose cone
Using the same amount of water in each rocket and pressurizing the water rocket launcher to the same psi can let you take a closer look at how fin and cone design, construction, and weights will affect the flight path (and height) of your soda bottle rocket.
- Find the best water level
In these soda bottle water rockets, the amount of fill you add in directly affects the height of your water rocket in similar ways that real space rockets also must handle. For example, the water rocket is propelled by the pressure in the soda bottle pushing the water out the spout, propelling the bottle in the other direction (up). One might think that filling the water rocket all the way up would be a great way to get higher heights, as more water will be able to push out the bottleneck. Try it. Fill the soda bottle completely up and see what happens. Once you have tried that, try having very little water, and a medium amount of water. Which one works best? There is a maximum height point that balances the amount of push the water inside has to the weight of the water. Can you find this fill point? Learn the science and find the answer here.
- Find the best launch angle
For this challenge, you want to keep the soda bottle free from fins or cones and be careful to fill the bottle to the same point each time, as well as pressurize the water rocket to the same psi. These are called our controls, and they help us isolate what we want to look at – her we want to see how only the launch angle affects the distance the soda bottle rocket goes, so we need to change only that variable and isolate the amount/weight of water and launch pressure. Using a protractor you can measure the launch angle that you will change from 0 degrees to 90 degrees and measure how far the rocket will go for a variety of angles in between. You can also check the theoretical best launch angle using the equations of motion in physics, a perfect activity for older students. Learn the science and find the answer here.
- Just have fun
Another idea is to just have fun with this project. Science doesn’t always need to be bogged down in graphical analyses, measurements, mathematical equations, etc. You could just have a blast with this activity and use it as a doorway to learning about how space rockets work.