Physics & Physical Science Demos, Labs, & Projects for High School Teachers

Balloon Rocket Lab

Posted on: December 19, 2009

Perfect image stolen from the internet

I admit I’ve been holding out on you.  Let’s just say I thought this one was a bit too low level.  I beefed it up and it’s perfect for my Conceptual Physics classes now.  I just did it this week and I like the results.

See that rocket shaped balloon on the right… good luck finding them.  I seem to only be able to find the regular party balloons.  Okay, I didn’t look that hard, but if they were at the local dollar store, I would definitely buy them.

So what’s the big deal about this lab, it seems almost grade school level?  First off, again, almost none of my students have ever built a balloon rocket.  This never ceases to amaze me.  Second, it’s deceptively challenging.  Lastly, the kids actually get the principles because of this activity.

To make this work in the classroom, I use a ringstand on one end with several book on the base for weight.  I tie a string and put it across the room, leaving the other end open so they can put straws on the string.  Each team gets their own ringstand/string setup.

The lab is broken into two missions.  The first mission is easy;  first, make it go across the room.  Then put the balloon at 45 degrees to the string and see what happens.  Then repeat for 90 degrees.  They sometimes guess that the balloon will spiral, most are surprised but figure out why it spirals.

Mission two is really difficult, I tell them they are being challenged, but they are not graded on success, they are graded on effort and documentation.  The mission is to make the balloon go down and automatically come back.  They are told they can use two balloons.  Once they get into this mission, the kids tend to put two balloons facing opposite each other and let go at the same time.  They seem to think that the balloons will know to take turns.  They learn first hand that the opposing forces cancel each other out.  That’s really the gem in this lesson.  I don’t care about them making it come back.

What most do next is blow up one balloon bigger than the other thinking it will move the way they want and then come back because it lasts longer.  Again, they usually figure out that the opposing forces cancel.  They next try to delay the release of one of the balloons.  I get a few creative ideas here using bent straws and twisted balloons, but so far no amazing designs.

I like to sit back and watch this one.  You can see the lights go on when they figure out the opposing forces cancel.  Below is the lab handout.  If you get some good solutions to the return mission, I’d love for you to post the solution here.

Balloon Lab – revised


10 Responses to "Balloon Rocket Lab"

This link shows a two-stage rocket. This could easily be modified to make a return trip design.

I’ve been racking my brains on Mission Two. I actually don’t think it’s possible 😦

…Has anyone come up with a successful design?

Yes, it is possible. You use a band around the first balloon that released the nozzle of the second balloon. You can make the band by cutting a strip from a 2-liter soda bottle. Blow up the return balloon and point it opposite the first, put the nozzle under the band, then blow up the first balloon.

Ideally, you need those long wide rocket balloons, but they are hard to find.

You don’t need 2 balloons or any extra supplies…the other “tank” is gravity! Set the string at a steep angle. The air from the balloon will push it up and gravity will pull it back down. Simple.

Haven’t tried the return mission, but I do love this one. I use it with College Prep, too. They have to get mass of balloon and straw, time and measure distance to empty and to stop. Then use kinematics to calculate acceleration and ‘deceleration’, and Newton to calculate forces. It’s actually our entry into friction: “Why does it stop?”

I like your addition. I’m officially stealing it.

Do you have a lab write up adding these kinematics? If you do, could you please send it my way?
Many thanks from an overwhelmed 1st year full-time physics teacher

I’m sorry, bug I don’t. I used to do this lab with my conceptual physics classes. I haven’t adapted this to my honors physics. Maybe someone else here can help.

Create a trigger that holds the balloon full of air that when it hits the wall it will release the air in the second balloon to comeback. Think springs and try to mold a paper clip into one

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