Balloon and bottle fountain

Safe­ty pre­cau­tions

Warn­ing! Only un­der adult su­per­vi­sion.

Equip­ment

• plas­tic bot­tle;
• bal­loon;
• straw;
• cap;
• any sealant;
• tint­ed wa­ter;
• awl.

Step-by-step in­struc­tions

Make a hole in the base of a plas­tic bot­tle. In­sert a bal­loon into the bot­tle as shown, fas­ten­ing it over the bot­tle­neck. Bore a hole in the bot­tle cap and thread a straw through it, and seal it with any sealant. In­flate the bal­loon and plug the hole in the base of the bot­tle with your fin­ger, pour in tint­ed wa­ter, and close the bot­tle with the mod­i­fied cap. Re­move your fin­ger from the hole and the foun­tain be­gins!

Process de­scrip­tion

The bot­tle is filled with air, and when we put the bal­loon on the bot­tle, we cre­ate a closed sys­tem in which the pres­sure is equal to at­mo­spher­ic. Our lungs wouldn't be able to in­flate the bal­loon if we hadn't bored the hole in the base to let out ex­cess air. Af­ter in­flat­ing the bal­loon, you need to plug the hole with your fin­ger so that the bal­loon doesn't de­flate. In fact, the bal­loon de­flates slight­ly when you close the hole. This caus­es the air pres­sure in the bot­tle to de­crease, and the re­sult­ing dif­fer­ence be­tween the at­mo­spher­ic pres­sure in­side the bal­loon and the re­duced pres­sure in the bot­tle keeps the bal­loon in­flat­ed. You may not even no­tice this de­fla­tion; such a slight change in the bot­tle's free space is nec­es­sary to keep the bal­loon in­flat­ed. When we let the air in, the pres­sure in the bot­tle is com­pared with at­mo­spher­ic and the bal­loon is blown away by the force of elas­tic­i­ty and there­by push­es the wa­ter out, form­ing a foun­tain. A small amount of wa­ter will re­main in­side the bal­loon – be care­ful dur­ing cleanup!