The natural world is full of observable processes that lend themselves to investigation. Have students research natural forces that shape land formations. They should choose one force, such as wind, rain or gravity, and find out how it helps shape mountains, valleys, canyons or anything else over millions of years. Alternatively, suggest that students investigate the water cycle. They can even build their own model weather system by letting water evaporate onto the lid of its container.
The laws of physics govern movement, yet rarely do students get a chance to consider them. Have students investigate the forces that exert themselves on physical objects. For example, students might choose to investigate what factors determine how far a baseball goes when hit by a bat, including mass, speed of the ball and wind resistance. Another idea is to have students research and test why two objects of different masses fall at the same speed when adjusted for wind resistance.
Physical life offers endless possibilities for scientific investigation. Suggest that students inquire into the processes of plant growth. For example, students can test how sunlight affects the growth rate of a plant by observing how two quickly two plants grow in differently lit rooms. At the same time, students can research and report about photosynthesis. Students also might investigate the effects of different kinds of foods on human brain function and energy level.
Your fifth-grade students are, no doubt, very familiar with technology but probably don't know how all of their gadgets work. Ask students to investigate the various factors affecting cell phone reception. For example, students can test how a cloudy sky improves or reduces reception. At the same time, students should research how a cell phone works and how its waves are transmitted. More generally, you can also suggest that students choose one gadget and research its operation and function at the library. Have students produce charts and illustrations to explain its complex processes.