We did this craft at most of our 7-to-12-year-old outreach programs this summer, and the kids all had a blast! The craft is fairly straightforward, but it’s challenging enough that the kids have to work to figure it out and usually need a bit of adult assistance.
This craft is a great way to practice important engineering skills as kids test our and improve their creations. We had kids experiment using multiple balloons or different sized wheels to try and figure out what could make their cars drive faster and better. There’s no limit to the ideas kids can come up with building these balloon cars!
Original craft found here. We adapted parts of this to make the cars work better and to have things run more smoothly with larger groups of kids. (Summer 2019)
Plastic bottle caps
Long drinking straws (the diameter should be big enough that a balloon pump can fit inside)
Small pieces of drinking straws
Tape (clear tape and either duct tape or masking tape)
A tool for poking holes in the bottle caps and water bottles
Anything to decorate your car
Bottle caps. Some bottle caps work better than others; plastic milk container screw-on lids work best, and Gatorade and Vitamin Water lids are also good. Some really hard plastic lids tend to crack when you poke holes in them, but you can test out different ones and see what works. For softer plastic bottle caps, you can poke a hole with a pushpin and then enlarge it easily with a screwdriver. The best tool to use is an awl if you have one, but just make sure to keep it out of reach of children.
Water bottles. Water bottle balloon cars need one hole in the top about a third up from the base of the bottle. An awl is the best tool for poking this hole too, but you could use scissors if you had to. Definitely don’t let kids try to poke these holes themselves. If you pre-do a bunch of these, mark the holes with a marker so the kids can find the holes.
- Gather your supplies: one water bottle, one balloon, four wheels, two stirrer straws, one drinking straw, two smaller pieces of drinking straw, scissors, and tape plus any extra materials to decorate your car.
- The stirrer straws are your car’s axels. Slide one small straw piece onto each stirrer straw. This will allow the car wheels to move once they’re taped to the bottom of the car.
- Slide wheels on either end of each stirrer straw. Use an awl or screwdriver to make the holes bigger if the wheels don’t fit, but avoid making them too big or they’ll fall off.
- On the side of your water bottle, directly opposite the pre-poked hole, attach your axels to your car. Tape only the small straw pieces sliding along your axel – make sure that you don’t tape the stirrer straw at all so it can spin freely. Duct tape works best for this, but kids have an easier time with masking tape (which doesn’t hold quite as well). Move your wheels close to the body of the car, but not so close that they are touching, and trim the excess stirrer straws. Try rolling your car across your table or floor to make sure the wheels all touch the ground and spin without sliding around.
- Cut off the lip of your balloon. This will help prevent air from escaping when you attach it to your straw.
- Tape your balloon to one end of the drinking straw using clear tape. Make sure that no air is escaping by blowing it up a bit with a balloon pump.
- Thread the straw in through the poked hole in the top of the car and out through the mouth of the bottle so the balloon ends up just outside the poked hole.
- Decorate your car!
- Try it out! Use a balloon pump to blow your balloon up as big as you want (but not too big so it doesn’t pop), set it on a smooth, flat surface, aim it away from other people (the balloon is at the front), and watch it go! If the car doesn’t work too well, try to come up with reasons why it’s having trouble – are all the wheels working?, is the balloon airtight?, is the surface smooth enough?, are your axels too long? Straight drinking straws sometimes work better than bendy ones, and cutting off extra length of straw that sticks out from the water bottle can help too.
TOILET PAPER TUBE BALLOON CARS
We also made toilet paper tube balloon cars which typically don’t go quite as far or as fast, but are easier and more fun to decorate and are a bit safer since any holes made in the body of the car can be done with a hole punch. For these cars, the stirrer straw axels go right through the body of the car, so you’ll need a template to show kids exactly where to punch holes for the axels to go. You’ll also have to punch a couple connected holes in the roof of the car for the straw to go through. Bendy straws work best for these to keep the balloon from dragging on the ground and the straw from interfering with the axels. You should cut off any extra length of straw that sticks out from the back of the toilet paper tube.