It’s so easy to make a balloon car that really moves! This simple STEM project teaches kids about physics in a fun and interactive way. See concepts like kinetic energy and Newton’s laws of motion in action! (Read more on those below.)
Use simple materials, like a water bottle and bottle caps, to create a balloon powered car that moves on its own! It’s SO FUN to race the cars and to see how far they’ll go!
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Use a recycled water bottle and paper straws to make a balloon powered car! It's such a fun STEM project for kids of all ages!
Author: Debbie Chapman
If you have really sharp scissors you can cut right through the skewers. Otherwise, cut through as much as you can and then snap the skewers off.
To do this, place the cap top up on a cutting board and push the screwdriver down into the center of the cap. Then pick up the cap and wiggle the screw driver all the way through until the hole is just large enough for the skewer to fit snugly into.
It should be a snug fit, but you can add some hot glue inside the cap to keep it in place if necessary.
Place a second bottle cap on the skewer, opposite to how the first cap was added, so both tops of the caps are pointing out.
Repeat with the other caps, skewer, and straw half to make a second axle with wheels.
Cut off the pointy end of the skewer so no one gets hurt. You can also trim the other end of the skewer if it sticks out too much. (We left between 1/4 and 1/2 inch outside the caps.)
Tape the straws to one side of a plastic water bottle, a couple inches in from each end. Make sure that the straws are perpendicular to the bottle so that the wheels roll in the right direction.
You can use patterned washi tape to help decorate your car, or simply use regular tape to attach the straws.
Place the bottle with the wheels down and put the second paper straw into the bottle's mouth, on an angle so it hits the top of the car/bottle.
Hold the straw so that an inch is outside the mouth of the bottle. Then mark an inch below where the straw hits the inside of the bottle. (You can either make an actual mark with a marker, or just keep your finger on the spot like we did.)
Remove the straw and use a craft knife (or scissors) to cut an 'X' shape where you marked on top of the bottle.
Push the straw in through the 'X' cut on the bottle, until the end of the straw comes out the mouth of the bottle. (There should be about 1 inch coming out the mouth of the bottle and 1 inch coming out the top of the bottle on the balloon end. )
Now put your mouth on the straw end that's sticking out of the bottle mouth. Blow into the straw, which will in turn blow up the balloon.
The elastic should keep the balloon in place and secure on the straw as it blows up, but if it leaks air you may need to adjust the elastic on the balloon or glue the balloon to the straw.
Now put your finger on the end of the straw to hold in the air, and then let it go to watch the balloon car drive away!
A balloon powered car is a simple machine, involving wheels (bottle caps) and an axle (the skewers). When you blow into the straw, air goes into the balloon and inflates it, creating potential energy. When you let go of the straw, the air in the balloon is released, and it becomes kinetic energy (energy from motion), and the car begins to move!
Normally when you let go of a balloon it flies all over the place, but the straw funnels the balloon’s energy in a specific direction, allowing the car to move in a straight line!
You can actually see all of Newton’s laws of motion represented in the balloon car!
Newton’s 1st law says that an object in motion remains in motion until an outside force stops it. This is shown in the balloon car, because the balloon car keeps moving until friction stops it.
You can also see Newton’s 2nd law (force equals mass times acceleration). Basically, the heavier an object is, the more force it will take for the object to accelerate (or move forward). The balloon car accelerates at a speed determined by the car’s mass (weight) and according to how much thrust the balloon gives it. (If you inflate the balloon more, the car will go further.)
Finally, Newton’s 3rd law of motion states that for every action there is an equal and opposite reaction. When you blow up a balloon, the rubber expands, which increases the pressure inside it.
Then when you let the air out of the balloon, the rubber contracts, and the air gets pushed out backwards. This is a reaction force that pushes the balloon forward, demonstrating Newton’s 3rd law.
There are a lot of fun things you can do with your balloon car:
The lighter your balloon car is, the faster it will go. Try using different materials to make the balloon car to see what works the best!
You can also minimize drag to make your balloon powered car go faster. Does the front of your car have any flat areas on it? A water bottle works well for this project because it has a curved shape that moves through the air more easily.
Friction is also an important factor, because it makes the balloon car slower. Make sure your wheels turn well, and aren’t wobbly, or else they may slow down the car.
Finally, you can improve the air speed as it releases from the balloon. First make sure that the balloon is airtight on the straw. Second, experiment with different straw diameters. Does a larger straw make the car go faster?
Your balloon car will drive crooked if the axles (skewers) are not facing perfectly forward. To make the balloon car drive straight, the straws holding the skewers must be parallel to one another and totally perpendicular to the water bottle.
The axles will definitely start wobbling after the balloon car has crashed a few times. Try re-taping the straws to the bottom of the bottle with new tape, or even using hot glue to keep them in place.
You can use different objects to make your balloon car or put the car together in a different way. Try some of the following:
Re-purpose recycling objects to make a super fun balloon car. Creating your own car out of every day items is such a fun STEM activity!
Our book Low-Mess Crafts for Kids is loaded with 72 fun and simple craft ideas for kids! The projects are fun, easy and most importantly low-mess, so the clean up is simple!
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You can purchase Low-Mess Crafts for Kids from Amazon, or wherever books are sold:
