My son is learning about force this week in science, so I thought making a balloon rocket would be a great experiment to demonstrate his concepts in a tangible way. He’s learning about Newton’s laws, friction, Since it’s Saturday and Dad is off, I decided to get the whole family involved.
Supplies
- balloons (9 or 12 inch work best)
- thin string (fishing twine, kite string, yarn, etc.)
- straw (not the flex kind)
- masking tape
Before we started, I gave our son the balloon and had him blow it up and then let it go (he LOVES to do this, he does it all the time!). We talked about what happened and why we think the balloon flies around crazy. Then I gave him all of the materials and I asked him how we could get the balloon from one side of the room to the other using only those supplies. We brainstormed with him and let him try a few of his ideas. This is a great activity for problem solving. He had to think about his supplies and determine the best way to use them. After a bit, we started the experiment.
We even paired up in teams: Boys vs Girls and raced our balloons!
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Building the Balloon Rocket Experiment
Tape or tie one end of the wire or string to a chair (you can tape it to a wall).
Put 1-2 pieces of tape across the straw (you can decide how many you need based on how wide your tape is).
Then, blow up the balloon. DO NOT TIE THE END!
Lift the balloon up and tape the straw to the balloon. Center the balloon under the taped straw with the part you blow in facing the wall.
Feed the other end of the string into the straw and pull it toward the side taped onto the chair.
Hold the balloon neck until you are ready to launch! Let the balloon go, and watch what happens!
Additional Tips & Tricks
- Perform the experiment with the string starting and ending at the same height, where the top is higher than the bottom, where the bottom is higher than the top, etc. and let the kids observe the different results.
- You can also do this experiment with different strings. Strings like kite string and fishing line will create less friction and the balloon will get to the end faster than on a yarn string.
What’s the Why?
Newton describes this effect in his Third Law of Motion: for every action, there is always an equal and opposite reaction. The air blowing out of the rocket (balloon) is the action, and the movement of the object in the opposite direction is the reaction.
When you blow up the balloon initially and then let it go. It flies around in a crazy pattern because the balloon opening (neck) is wobbly, therefore, the flight path of tbe balloon is wobbly, too. The air escaping the balloon pushes out in every which way (remember this is the action), and the reaction of the balloon is to move the same way.
So, we use the straw to stabilize the direction of the balloon. Creating a straight track for the balloon to follow (transnational motion). This path makes it’ easier to see the direct relationship between the size of action (the amount of air escaping the balloon at once) and the reaction (the distance the balloon travels). The force produced by 2 balloons of the same type that are inflated to different sizes will be the same. BUT, larger balloons will travel farther because they have more “fuel” (air).
Questions to ask to get them thinking?
- What is the force causing the balloon to go forward?
- What direction is that force?
- How can we make the balloon travel further along the string?
- What do you think would happen if you change the size or shape of the balloon?
- What makes the balloon stop?