This is a great experiment that is easy to perform with items you probably have around the house. All you need is a D battery, 2 shiny clean pennies, aluminum foil, masking tape, and two metal paper clips.
Fold aluminum foil into two separate strips. Tape one strip to the positive and the other to the negative battery terminal. Fasten the foil strips to the pennies using the paperclips. Allow your project to sit for a couple of hours.
When you remove the pennies you will see a greenish stain where the penny connected to the positive terminal was connected. The positive terminal gave the copper in the penny a positive charge. When those positive charged particles combine with the potato’s negative particles they react leaving the copper residue. Thanks to this experiment you can always tell which side of the battery emits a positive charge.