The most popular science fair topics include carbon dioxide and global warming; the effect of oil spills on aquatic plants; peer pressure and gender; and the effect of classroom temperature on student performance. Popular projects include experiments in environmental science, behavioral science, sports science and chemistry.
Biology projects are popular at science fairs. Popular biology experiments include measuring whether singers have larger lungs than non-singers, testing whether hamsters are smarter than mice, and determining the usefulness of plant growth enhancers.
Students who are interested in sports may perform a sports-related science fair experiment. Some hypotheses include that a swimming cap makes a swimmer swim faster, that listening to music increases an athlete's performance, and that girls with longer ring fingers have more athletic ability than girls with short ring fingers.
A popular science fair project for elementary school students is mapping the energy use of the classroom. Students need only graph paper, pencils and some colored pencils or crayons. Students draw diagrams of the classroom on the graph paper and mark locations of electrical outlets, specifying which are in use and which are not. They then map items in the classroom that need energy but are not plugged in. By doing this in several classrooms, students can determine which classrooms in the school use the most energy.