Super Simple Balloon Car

A few days ago, I came across a post from Steve Spangler Science detailing how to build your very own balloon-powered car.

Although my oldest is only four and rather too young for the building part of the project, I knew we had to try this. I was lacking a few of the pieces the project called for, though, and I hated to make a run to the store with my three small children just to pick up a package of wooden skewers.  Suddenly, I had a brainstorm: use one of the kids' Duplo train car bodies as the platform!
It was as easy as it sounded, and both of my older kids had a blast playing with the end product.

Materials

• Balloon
• Drinking Straw, preferably with a bend in it
• Rubber Band
• Tape
• Scissors

Instructions
As the inspiring blog post suggested, I cut off the rolled neck of the balloon so it would be easier to seal to the straw.  I then slipped the bent end of the straw into the balloon, folded the excess around the straw, and sealed with a small piece of tape.

Finally I laid the straw down the center of the Duplo car and attached it with a rubber band looped around the body. I bent the straw so that the balloon would point up: otherwise it drags on the ground until it deflates.
That's literally all there is to it.
To use, inflate the balloon by blowing into the straw. Pinch it shut with your fingers, set the car down on a hard surface, and let it go.

Analysis 
Neither really has the combination of lung power and coordination to inflate the balloon, pinch the straw, and let the car go before losing all the air, although James eventually was able to make it work a little - much to his delight.

I made several using the various Duplo cars that we found in our stash.  The fancy one with the metal axles (it came with a fire truck body just this Christmas) worked much better than the traditional train cars, simply because it has a lot less rolling resistance.

Although the bent-neck straw was an elegant solution to the problem of the balloon dragging on the ground, the small diameter of these straws did not allow air out fast enough to get much speed on the car. It would probably work fine with a lighter vehicle.
A large diameter straw such as the ones from McDonalds made the balloon easier to inflate and drove the car farther.