Richard Gawel, age 10, of Toronto, Ontario, Canada, for his question:

What causes gravity?

This is a problem of how and why    which are two very different things. Several generations ago, Michael Faraday figured out how a generator can create electric current. We still don't know exactly why this happens. Way back in the 1600s, young Isaac Newton figured out precisely how gravity works. We still don't know exactly why it works as it does. Naturally, numerous research teams have tried to find the answer to the same question that puzzles you. But at present, they cannot explain exactly what causes gravity.

However, we do know that this well behaved force is built into every speck of matter. Every molecule of solids, liquids and gases has its minuscule quota of built in gravity. The quota increases when large amounts of matter are massed together. We also know precisely how it works. Because centuries ago, a certain young genius figured out the laws that govern the force of gravity    and stated them in simple terms that any young student can understand.