A fun and relatively simple science project could be on airplanes and flight. This project would center around researching and presenting the basic building blocks of how planes fly. Student can hypothesize about how a plane flies, then analyze how wing design creates lift. The project could also feature the history of human flight. Visual material could include a homemade video of the student flying a toy airplane. Present your hypothesis, research, materials, procedure and conclusion on a trifold board.
Another science topic could look at how gravity works using a gravity well that features a bendable material, such as rubber, laid over the top of a large bowl or trash can. An object is placed in the middle, so the material bends. Roll a smaller object, such as a penny, around the outside of the material. This demonstrates that gravity isn't a force, but a bending of space. Student can hypothesize about how this relates to our solar system.
Another science project involves electricity, building a simple potato battery to power a small lightbulb. Simply take a potato, insert a galvanized nail and a copper wire into it (close together but not touching). Run an electric wire from the galvanized nail to the lead on the small lightbulb socket, and repeat with the copper wire; multiple potatoes can be linked together in this fashion. Kits or small lightbulbs for this project can be found at toy stores, science stores or science project websites.
A project on pulley, featuring the basic laws of physics, would analyze mass, force, distance and work. Take an object, such as a stapler, and weigh it. Build a pulley system with a wheel and a piece of rope. Tie the rope around the object and run it through the pulley. Record the amount of effort and rope it required to lift the object a certain height. Repeat the experiment with increasing numbers of pulleys. Record how your findings changed based on the number of pulleys used, force needed and length of rope pulled.