SUBMARINE!

Get a 16oz plastic soda bottle.... attach some form of ballast to one side... put holes in the bottom to let water in... holes in the top to let air out... attach a balloon to a hose & insert it into the bottle...... fill your sink & let it sink to the bottom.... blow into the hose the balloon will fill & it will subsurface.... blow hard & It will surface....

Fun, boat oriented, & my 11 year old got an A for it!

Good Luck!

An automatic ''handle jiggler'' for the toilet hooked to a ''clapper''.
You could call it the''CRAPPER CLAPPER''. Saving unneeded trips back to the restroom............Roger 1

My daughter just had the same type of project. She made a keyless / remote front door of the house. Using a car remote as the model, took some pic.s of point remote at the door then opening the door without fumbleing for keys.