Public policy is a far reaching subject that has worked it's way into many other fields of study. Public and environmental policy is a topic you'll discuss a lot in political science courses and environmental science classes.

A good environmental project could be:

What type of water is better for plants? Tap water, Distilled water, or Microwaved water.

hope this helps

International relations and foreign policy

A science fair about that topic would be catorigized as physics.

Ethically conducted science seeks to inform rather than influence policy.