Make a Balloon Rocket in 6 Steps

Tape a balloon to a straw, thread it onto a string, and watch it race between trees.

 

Materials you'll need

• 1 ball of string (long enough to stretch between two trees)
• 1 plastic straw
• 1 balloon
• 1 clothespin
• tape
• 2 trees, posts, or chair backs to tie to

 

Step-by-step tutorial

Step 1: Grab your string and tie one end tightly around a tree trunk or a low branch. Give it a tug to make sure the knot holds.

Step 2: Thread the loose end of the string through a plastic straw and slide the straw all the way down to the tied end.

Step 3: Tie the loose end to a second tree, pulling the string as tight as you can. Tie that end higher than the first if you want your rocket to climb uphill.

Step 4: Blow up the balloon, then pinch the neck shut with a clothespin instead of tying a knot. The clip holds the air in until you're ready to launch.

Step 5: Tape the balloon to the straw with the clipped neck pointing back toward the tree you started from. That's the direction the air will shoot out.

Step 6: Unclip the clothespin and watch your balloon zoom off down the string!

Learn more

A balloon rocket runs on Newton's third law of motion: every push comes with an equal push back in the opposite direction. Stretched rubber squeezes the air inside the balloon, so the moment you unclip the neck, that air rushes out the back. The balloon pushes the air backward, and the air pushes the balloon forward with exactly as much force. That forward push is called thrust, the same force that lifts real rockets off the launchpad. The straw and string don't add any power of their own. They just keep the balloon from spinning off in a random direction.

If this one was a hit, Bottle Rocket Blaster takes thrust further with a chemical reaction that builds enough pressure to launch a rocket straight up instead of along a string.