Designing an Efficient Balloon Car

        Friction between the wheels and the ground was a big concern.  We tried a bunch of different wheels to see which ones rolled the best.  We settled on using CDs for the wheels since they had enough friction that they could grip the ground, but not too much that it slowed the car down.  We also had to worry about the friction of the axles spinning.  When we would have the wheels spinning on the ends of a stationary axle, they slowed down too easily.  We then used a dowel rod through a straw so that the wheels would spin at the same time.  The whole axle spinning worked better than trying to get the wheels to spin freely because the wheels could get more easily caught on something than just a smooth wooden rod rubbing against the plastic straw.  

        One of the major changes we kept making was the design of the body.  We originally had a triangular body, but when we attached the balloon to it, the balloon was angled upward.  Since horizontal motion has nothing to do with vertical motion, we knew any air going upward wasn’t pushing the car forward.  So we changed the body to a flat surface so that we could have the air going straight out behind the car and use the majority of the thrust to move the car forward.

        Putting all these different aspects together helped us to build an effective car.  For the thrust, we used Newton’s Third Law to design it.  We tested our wheels based on how much friction was created.  Because vertical motion has no affect on the horizontal motion, we knew all the thrust had to be horizontal, so we knew how to orient our balloon on the car.  The principles of physics helped us to build an efficient balloon car that has the speed and stamina desired.