Hi, we have to build a Balloon Car..what are some things to consider to make it the fastest and farthest car.?

Question

how should it look like,
what materials and how and why does it go fast

Answer 1

A tubular shaped balloon should do better than a big fat one because of lowered air drag. A larger balloon will have more air available for thrust, but will require a larger carriage to hold it.

Experiment with nozzles to restrict and direct the airflow. Restricting the airflow extends the time over which thrust is delivered but, of course you can't restrict it too much. Try to keep the flow as laminar as possible. Turbulence in the flow will cut the thrust

Keep weight to a minimum

Pay attention to your wheels and axles. Use graphite lubrication on the axles. Use large, hard, thin wheels. Small wheels and soft wheels increase the rolling resistance. Wide wheels increase rolling resistance. Make sure that the wheels all are pointing straight. Test the carriage without the balloon by rolling it down a slight incline. Get that part working well before worrying too much about the balloon.

Have spare parts, especially spare balloons of exactly the same type that you practiced with, ready on race day. Apply a new coat of graphite to the axles on race day.