Interesting submarine

During the summer vacation, the school arranged to make a small production called "Plastic Bottle Submarine", and I also made one, and the effect was not bad.

This "submarine" is easy to make: first prepare a plastic bottle and two plastic pipes.

A small amount of plasticine and cardboard. The tools needed are also common: scissors, blades and awls. By the way, there is also an indispensable plastic insulating waterproof tape (rubber tape).

Cut the bottom of the plastic bottle evenly with a blade, put a small piece of plasticine in the bottle and fix it with plastic insulating tape (rubber tape) as ballast. Then drill two holes in the bottle cap, insert two plastic pipes, one long and one short, and fix them with adhesive tape. Then use adhesive tape to fix the just cut bottle bottom in place (pay attention to sealing). Then make a "command tower" out of cardboard, and color both sides with crayons (waterproof). Just decorate it at last!

I found a longer basin, filled it with more than half of water, and slowly put the "submarine" into the water. Water flows into the bottle from the plastic pipe below. When the bottle is full of water, the submarine sinks to the bottom of the water. At this time, the mouth blows slowly and evenly from the plastic pipe above, and you will find that a long string of blisters will emerge from the underwater plastic pipe mouth, and then water will begin to come out. The submarine advanced slowly and rose while sailing. If you stop blowing, water will flow into the bottle again and the submarine will sink again. And when you are blowing, block the nozzle of another plastic pipe immersed in water with your finger, and water will flow out of the pipe you are blowing. If you take out the submarine full of water, turn it upside down and put two plastic pipes down, you will find that only one pipe is draining water, while the other pipe is sending air into the bottle. When the outlet pipe is blocked, the other pipe becomes the outlet pipe, and the original outlet pipe becomes the outlet pipe.

After a series of experiments, you must have many doubts. First, why does the submarine float when it sails forward when it blows? Because after the air enters the bottle, the water in the bottle will flow out from another pipe under the pressure of the air, and the water in the bottle will be discharged, and the submarine will naturally float up. As for the sailboat, it is because the discharged water has a reaction force, which will push it forward slowly.

Second, why do you plug the nozzle of the submerged plastic pipe and water will flow out of the blowpipe? Because the water in the bottle must be discharged through the plastic pipe, which is the only outlet channel, if the water loses its outlet channel due to air pressure, it will naturally be discharged by blowing the pipe, and the pressure will urge the water to flow to the place where the gas enters.

Third, why do you turn the submarine plastic pipe upside down, one will come out and the other will come in? Because "water flows downwards", water will definitely find a lower channel to flow out after being reversed. After selecting the lower pipeline, the higher pipeline will naturally enter the air. Because after the water is discharged, the volume of water in the bottle will gradually decrease, and the other part of the bottle will be filled with air, prompting the air to enter through the plastic pipe.

Through this experiment, I understand a lot of scientific truth, and at the same time I understand that only by experimenting and demonstrating in person can I get the most scientific and accurate answer!