In creating our balloon car, we used many physics principals to change the designs until we had a well performing car. The different principals helped us to change certain aspects of our car so that every part worked well together. The principal that with every action there is an equal and opposite reaction is what we used for the thrust of our car. We based our wheels on what ones caused the least friction. We used the fact that vertical motion has no affect on horizontal motion to determine how to orient our balloon on the car.
These different pieces of the car working together help it perform well.
For the thrust of our car, we used a balloon attached to a PVC pipe. This pipe allowed us to let the air out of the balloon more quickly. It also helped us to direct the air straight back from the balloon. The more air we were able to release, the more negative horizontal acceleration we could have.
However much acceleration there is in the negative is how much there will be in the positive because of Newton’s Third Law of Motion. The more air that is released in the negative will push the car forward faster. We needed the car to go 1 meter in 3.
5 seconds, and it needs to cover 10 meters. We tried different sized pipes and straws until we found a good balance between speed and distance. 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.