As Energy Quest points out, good physics projects require a problem to be solved, a hypothesis regarding the solution to the problem, and an experiment containing a control, an independent variable and a dependent variable. Science Buddies offers many ideas for investigatory physics projects containing these important elements, including experiments investigating magnetism, acceleration, light and sound.
Among the investigatory physics projects suggested at Science Buddies, one involves levitating magnets that are placed so as to attract or repel one another. A related project involving magnetism uses a magnetic levitation kit to test how much weight a maglev (magnetic levitation) train can carry. One classic physics experiment recreates Galileo's and Newton's work on acceleration by using a metronome to determine the relationship between elapsed time and distance traveled.
A physics project that studies the way different geometric shapes scatter light investigates the basic principles of stealth technology. Other physics experiments involving light explore what happens when primary colors are added to or subtracted from visible light. Another experiment measures the varying intensity of compact fluorescent bulbs compared to traditional incandescent light bulbs.
Students who are interested in acoustics may want to try an experiment which tests the sound absorption properties of acoustic foam compared to other materials. Another sound-related project uses a decibel meter to test the auditory range of the human ear.