Hands-on activity: Soda bottle rocket

Tape your sticks around the bottom of your bottle so they poke out like lander legs.

• The sticks should all extend about an inch past the neck of the bottle. They should be even, so the bottle can stand on them and stay balanced. 

Add whatever you want to the outside of your rocket, so long as it’s not heavy!

• Paper fins or a nosecone will make your rocket move through the air more smoothly (and also look cool).

If you don’t have an actual cork, you can make your own with sponge and some plastic wrap.

• Roll up the sponge and wrap it tightly in plastic. See if it fits the neck of your bottle. You want it snug enough to be watertight, but not more tight than that.
• If it’s too big, unroll the sponge, cut a strip off of it using scissors, and try again.
• WARNING: Be careful not to push the sponge all the way into the bottle!

Find somewhere outside where your rocket can sit on its legs and stay balanced. 

• If you want, you can design your own custom launchpad out of a cardboard box.
• There shouldn’t be anything around your launchpad that you don’t mind getting wet. 

Flip the bottle over and pour in vinegar using the funnel.

• Pour in two cups of vinegar if you're using a two-liter bottle, or one cup if you're using a smaller 12-ounce bottle. This might not be the perfect amount — you can try adding more or less to your rocket after your first launch.

Scoop two tablespoons of baking soda into two squares of toilet paper (if you're using a two-liter bottle), or scoop only one tablespoon if you're using a one-liter bottle.

• Fold the paper around the baking soda until it’s small enough to fit through the neck of the bottle, but keep a little tail of paper that sticks out a couple inches.

Dangle the packet into the soda bottle. Put the cork in so that it traps the tail of paper against the bottleneck, keeping the packet hanging.

• This is the hardest part! Feel free to ask for help.
• Check your cork. If you push it in too tight, the rocket won’t launch. If you push it in too loosely, the cork will pop off too soon.
• It’s okay if you don’t get the tightness right on your first try — science is about experimenting! 

Set the rocket down on the launchpad. The cork should now be facing downward. 

• Retreat! Back up at least 10 steps.
• Count backward from 30. Your rocket should take about that long to launch, but it could be faster or slower!
• The baking soda and vinegar are combining to make gas that builds up inside the bottle. The pressure pushes out equally in all directions (on the cork, the sides, and the top of the bottle). 

Success!

• When the cork pops, the gas finally has an opening and rushes out.
• Explanation: As the gas escapes downward, it pushes itself out. But the gas is also pushing upward on the top of the rocket with the same amount of force — the gas just can’t escape in that direction. So, the rocket gets pushed up while the gas flies down. This same basic principle applies for even the biggest rockets, like the Saturn V or the Space Shuttle.
• WARNING: If your rocket doesn’t launch after a couple of minutes, an adult should slowly remove the cork, being very careful because pressure will have built up inside the bottle. Then you can try again from Step 4, putting the cork in less tightly this time.