this instructableWater Bottle Rockets are a terrific demonstration of Newton's Laws of Motion. I have been launching these rockets with my 7th graders for the past 10+ years. After a number of prototypes, I'm ready to share a project that anyone can build and test. The best part, it only takes about an hour to build! These rockets will easily fly 150 feet with some of the better projects traveling well over 300!

Warning! There is always risk involved when subjecting bottles to high pressure. There is also risk due to the uncertainty of where a rocket may land. Keep all spectators behind and away from the launch area / anticipated landing area.

Supplies

2 Liter Soda Bottles (3-4)

Foam Core for fins

Packing Tape or Duct Tape

Scissors

Box cutter

Hot Glue Gun and Hot Glue Sticks or Super Glue

Spray Paint or some way to decorate the rocket

A water bottle rocket launcher kit. I purchased two so that students can pick a buddy and launch simultaneously. (LINK to the one I've used for many years. Pay no attention to the terrible reviews. They all have the same issue. The instability of the two prongs is an easy fix and I'll show you how in this separate instructable.)

Air compressor or Bike pump

Water

Step 1: Reduce, Reuse, Recycle

Want to know what's better than buying your own 2 Liter soda bottles? Raiding a neighbors' recycling or taking a few bottles home from a party you've attended/crashed. Although it only takes about 1 hour to build one of these rockets, I give my students 3 weeks notice (so they can find creative ways to collect the bottles). If your hunt for used bottles is a bust, you can almost always find a brand on sale. This year, I found a 5 for $5.00 deal on Pepsi products. I prefer the Pepsi bottles over the Coca-Cola brand bottles because of the shape of the bottles. We purchased A&W Rootbeer to make a few rootbeer floats and poured the rest down the drain.

Step 2: Cut Bottles

Do NOT cut one of your bottles. This bottle will serve as the bottom of your rocket and must hold the water and air pressure. This bottle will not be referred to as the BOTTOM BOTTLE. Even the slightest pinhole in this bottle will cause the rocket to fail. Remove the label and set the BOTTOM BOTTLE off to the side.

Now that you've set your BOTTOM BOTTLE off to the side and PROMISE YOU WILL NOT CUT INTO IT, gather your remaining bottles.

1. Remove all labels

2. Find the line in the plastic where the factory joined the bottom of the bottle to the main cylinder.

3. Puncture the bottle on this line with a box cutter or knife. Be very careful! This is a good time to have some adult supervision.

4. Use scissors to cut along the line until you remove the bottom portion of the bottle.

Repeat these steps for the rest of your bottles so that you can assemble the body of your rocket.

Step 3: Join the Bottles Together

Take one of your bottles (with the removed bottom) and fit it over the BOTTOM BOTTLE. The spouts of the bottles will be facing away from one another. Because the bottles have the same circumference it will be a tight fit.

Make the bottles as straight as possible.

Take your next bottle with the bottom cut off and place it on top of the previous bottle.

Make sure all three bottles are as straight as possible.

Repeat until your rocket is an ideal length.

Use packing tape or duct tape to join the bottles at the seams. (Helpful hint: Before taping the bottles into place, it's a good idea to roll them along a flat surface. If the bottles wobble, it indicates that they aren't straight.)

Step 4: Cut and Glue the Fins

Determine the number of fins you want to add to your rocket.

Use a box cutter and a straight edge to cut your foam core into triangles.

Run hot glue (or superglue) down one edge of your triangle. *Caution! Burns possible. Adult supervision recommended. If using hot glue, be careful not to touch the glue or the nozzle of the glue gun. I'm all about experiential learning, but not when it comes to 3rd-degree burns.

Glue the fin onto your BOTTOM BOTTLE and make sure it's directly in line with the rocket. This is one of the more important steps in making your rocket fly super far!

Space your fins around the BOTTOM BOTTLE evenly.

Your soda bottle with fins should be looking like a real rocket! Although its currently ready for liftoff, one of the best parts of building the rocket is the decoration/personalization.

Step 5: Decorate Your Rocket

An easy way to decorate your rocket is with spray paint. Keep in mind, you don't want your decorations to hinder the flight of your rocket. Covering the whole thing in decorative duct tape might look cool, but will add quite a bit of mass.

Many of my students will get together and have a rocket building/decorating party. Their creativity never ceases to amaze me!

Step 6: Launch the Rocket

There are a number of different launch set-up kits that can be purchased online. I have used THIS KIT for many years and find the quality of the materials built to last.

First, add about one liter of water to the BOTTOM BOTTLE. (It's good to have a hose spigot close by and a 5-gallon bucket). This is approximately 2 Solo Cups worth of water.

Connect bottle to the launch kit (This can take some practice because it takes some leverage to get the rubber stopper into the mouth of the bottle).

After the bottle is secured to the launch kit, pressurize the bottle. The launch kit has a valve for pumping up the bottle (like you would find on a bicycle). You could use a bicycle tire pump, but it takes a lot of work and the time between launches increases. If you use an air compressor, getting the pressure up to around 90 psi only takes about 10 seconds.

Stand back, pull the string with a quick flick of the wrist, and watch it fly. You will need a large area to launch over (football field or soccer pitch).

When I do this activity with my students after everyone has had a chance to launch the kids can retrieve their rockets. If the rockets are in good shape (still have fins/nose cone can be straightened out) they can launch again. This is where I allow them to test out different amounts of water/different air pressures/different launch angles. If the rocket launched well the first time, I might bump the pressure up to around 100 psi.

I can usually go for about 3 years (launching 70-80 rockets each year) before the rubber stoppers wear out. I'm sure I could launch more rockets per year, but the rubber stopper tends to dry-rot after so many years. With the high pressure, the hoses have the potential to leak. This can be fixed by adding a few rubber bands (wrapped around) where the water or air is leaking to help create a better seal.

The major complaint about the launch kit (on Amazon) is stability. If you want to learn how to build an easy launch pad that will last for years, HERE is the instructable I created to take you through the steps.

Now go build a rocket!