How a submarine rises and sinks

How does a submarine rise and sink?
Equipment: large container with water, empty bottle, coins, electrical tape, silicone tube, balloon, rubber stopper, drinking straw, scissors, hot glue.
Make holes in the top and bottom of a plastic bottle. Bore another hole in the middle of the cap and pass a silicone tube through it. Put a balloon on the end of the tube and seal it with electrical tape. Insert the balloon into the makeshift “submarine” and cap it. Use electrical tape to attach a ballast of coins to the bottom of the submarine, glue a rubber stopper on top with hot glue, and insert a straw. Your submarine is ready!
Use a syringe to supply air through the tube - inside the “submarine,” the balloon inflates. When placed in an aquarium with water, the “submarine” stays on the surface. By removing air from the balloon with the same syringe, you can make it sink. You can control its diving depth this way!
When a body is placed in a liquid, a buoyant force proportional to the volume of the immersed part of the body acts on it. If the buoyant force exceeds the force of gravity, the body will float on the surface. When the bottle is filled with water, its volume remains unchanged, but its mass increases. At a certain moment, the force of gravity exceeds the buoyant force, acting on the submarine and causing it to sink. When air is supplied, the balloon inside the submarine inflates and displaces the water, which reduces the force of gravity acting on the bottle, and when the force of gravity becomes less than the buoyant force - the submarine rises to the surface.
More awesome experiments await in the MEL Physics subscription!
Warning! Only under adult supervision.