A science fair is a time to showcase experiments and projects that ask a question, and then seek to find the answers. Depending on your grade level, you might be able to choose your own science fair project, or you may have a list of projects you can choose from. Either way, you can find projects and experiments that not only get you a good grade, but actually do some good for society.
Recycling is one way to benefit society because it eliminates waste, leads to less trash in landfills, and can also help produce energy. A project on recycling, whether it is exploring new or different options or figuring out how to raise awareness of it, is always a benefit to society.
Sometimes controversial topics are good for society because they encourage people to debate and make decisions about the long term risks and benefits of something that isn't popular today. Doing a project on donating blood, drug abuse education, or STDs might seem like you are entering a controversial area. However, if you bring awareness to a topic and get people thinking and talking about it, you can benefit society - especially if your project leads to a specific conclusion that is positive.
Alternative energy is a hot topic, but almost everyone can agree on the fact that it is a good idea to explore some renewable resources and see if they'll make a difference. Doing a project on wind power, water power, or solar energy is a good way to promote ideas of healthy experimentation with energy. You can make your own power generator with water, sunlight, or wind, or you can do an experiment on how much energy can be produced.
New Ways of Doing Things
A project that delves into new ways of doing things can be very helpful for society as a whole. Choose a project that researches ideas about how to do something in a new way, as long as the change is good for society as a whole. A project on a different way to produce energy, a different way to recycle trash, or a different way to commute or share the road can all be good for society in general.