The first step to attach a balloon to a car is to attach the balloon to a large straw. The straw provides a stable structure to attach to the car. Here is how to attach a balloon to a large straw.
The second step is to attach the balloon and straw to the car. This video shows one way.
As students attach the straw and balloon, they will need to solve two problems:
How do you keep the balloon from dragging?
How do you keep the car from tipping?
Some students use a large box instead of a flat cardboard sheet. The box holds the balloon, but usually is too heavy . The problem off the car tipping is a problem of weight distribution. The best way to solve it is to re-position the balloon. Another solution is to add weights to balance the balloon, but that makes the car heavier.