Under water, the pressure under the empty bottle is greater than the pressure above, so the bottle is compressed more and more when it moves down. This is different from the situation on water, because on water, the pressure at the top of the bottle is equal to the pressure at the bottom. When the underwater pressure reaches a certain level, the mineral water bottle begins to be pressed by the force, so that the air penetrates into the bottle from the bottle mouth and compresses the air into a gas state.

Under water, the pressure of water increases, and the air pressure in the bottle and the external pressure increase continuously, so that a load-bearing object heavier than water can be formed. This makes the bottle sink to the bottom gradually. After deflation, the air escapes again, so that the pressure of water and the bottle is rebalanced and the bottle floats to the surface again under the buoyancy.

Simply put, the principle of mineral water bottle submarine is to use the buoyancy and pressure principle in physics to compress the air into a heavier object and make the bottle sink to the bottom of the water. After deflation, the air diffuses and the corresponding gas volume becomes larger. At this time, the total volume of the bottle becomes larger, and the buoyancy is greater than the weight of the bottle, so the bottle can float.

Production method:

1, making the hull. Cut out a rectangular hard foam board with a knife, which is about twice as long as a mineral water bottle and about 1-2 cm wide. Draw a middle line on the long side and fold it in half. Then draw a 2 cm mark around the folding line, and draw a line from the two marks near the long side to both sides, intersecting the short side respectively.

Cut inward along these two lines with a knife to form a triangle with sharp ends at the head and tail.

2. Make two small holes in the center of the hull, insert lead blocks and fix them. This can slow down the sinking speed of the mineral water bottle submarine and make it easier to tilt the bow.

3. Stick 1-2 layers of aluminum foil on the back of submarine hull to make its surface softer, so as to stick various toys and stickers.

4. Cut the mineral water bottle in half along the middle, leaving the bottle mouth and bottom. Turn the bottom of the bottle upside down, flatten it and stuff it into the center of the hull. Fix the inclined bottle bottom with the bottle body with a messenger wire.

5. Stick a piece of scotch tape on the bottle mouth and fix the bottle mouth in the center of the bow. Put the messenger wire through the bottle mouth and empty the air filled in the bottle, so that the submarine can sink.

6. Hang a heavy object (such as lead) at the bottom and stern of the mineral water bottle to keep the submarine sinking steadily.

After making, fill the mineral water bottle with water (not too full, or the submarine will float), and then press the bottle to let the gas out. As soon as the gas comes out, the mineral water bottle submarine will quickly sink to the bottom of the water, releasing the water on the suspension line, and the submarine will swim like a small fish!