How about an experiment like "Test if Water is Salty Using Electricity." This you can do a good graph too. You get the buzzer to go off, making your graph from little or no salt to a very large amount of salt. Good luck.
A good science project i did was with 2 glasses first i put equal water in both glasses and put in one glass 3/4 of salt mixed in with the water and i put 3/4 of sugar mixed with the water.Make a screw hang above the water in both glasses which u can tie string to to a pencil and the string to the screw,MAKE SURE DONT LET THE SCREW TOUCH THE WATER.