Did you know that you can power a clock from food? You can use lemons, potatoes, tomatoes, etc. It's an alternative energy source other than batteries. You can buy a kit for a lemon or potato clock.
Here is the science behind the experiment:
"The powering of the lemon clock works by a process of electrolysis. The copper plates play the role of the positive electrodes of a battery, and the lemon itself plays the role of the battery.When the copper and zinc plates are inserted into the lemon, a chemical reaction takes place where the electrons with a negative charge move from the zinc plates to the copper plate to form a current.
The juice of the lemon is an acidic electrolyte which is a liquid containing moving ions – allowing for this electric current to pass through."
Let your kids experiment to see which food is the most effective energy source for the clock.