Soda Bottle Rocket Car-Physics of Toys // Homemade Science with Bruce Yeany

All right, go. Go. Hello, I'm Bruce Yeaney, and today we're going to take a look at soda bottle rocket cars. Go? Go. Yes. 360. Now, in a previous video, we took a look at soda bottle rockets that we could use inside, and these run on compressed air supplied by a foot pump. Now, with these rockets, they get filled three-quarters of the way with water. We pressurize them with air, so we definitely have to use these outside. With these rockets, there's a good chance of getting wet. Let's start by taking a look at the cars. This first frame was cut out of plywood. Now, the wheels have bearings in them. They turn very easily, and the bottle sits in the two supports, and it's held there by these thick rubber bands. Put that one in place, and this front one, and you'll notice that the bottle is on a slight angle. Rolls very easily. Now, the second one, similar design. Once again, it's made out of wood with the same type of wheels, and this car puts the bottle on a little bit more of an angle. It's this angle plus inertia that ensures it's the water that leaves the bottle first. As the car accelerates, it gathers at the back end of the bottle. The bottles are pressurized to about 75 pounds per square inch, and when it's released, the car is a good example of Newton's third law. The car moves forward because the water is pushed backwards. If we look very closely, we can see just about all of it leaves the bottle. Now, I also experimented with the bottle itself. The first trials were run with a plain soda bottle, and I found it was just too powerful for the car to handle. The car would often flip over. Here we see the stream lifting the back end up, and the stream was so powerful, it even broke the connector off the pump. Now, to slow that exhaust down a little bit, I took a short piece of PVC pipe, and I glued it right into the opening using a plastic cement. Now, another variation was to extend the throat down into the bottom of the bottle. The PVC was heated, bent, and then glued in place. These changes gave us a bit more control and still plenty of speed. My first attempts had the stopper held in place by friction. That got us up to about 20 psi. The car moved, but not very fast. We needed more pressure. Here's the locking mechanism for the stopper. It starts with a threaded coupling that slides over the bottle, and then a bent wire is pushed through it, locking it in place. There we go. Next, we're going to add the stopper and valve. I'm going to push that down, and finally, we're going to use a threaded cap, and I'm going to hand tighten this, and that's going to hold the stopper in place until we're ready to release it. The pump has a locking mechanism that attaches to that valve. It'll take about 25 steps to get this bottle up to 75 psi. That's about as high as this pump will go. Now, the final piece is this release bar. The rope is attached to that pin. The bar goes up against that collar, and I simply pull on this rope hard enough, it pulls the pins out. The stopper and collar are released, and off they go.