How a submarine rises and sinks

Safe­ty pre­cau­tions

Warn­ing! Only un­der adult su­per­vi­sion.

Equip­ment

• large con­tain­er with wa­ter;
• emp­ty bot­tle;
• coins;
• elec­tri­cal tape;
• sil­i­cone tube;
• bal­loon;
• rub­ber stop­per;
• drink­ing straw;
• scis­sors;
• hot glue.

Step-by-step in­struc­tions

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!

Process de­scrip­tion

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!