Albert Nead, age 10, of East Greenbush, New York, for his question:

What makes gravity?

We know a lot about gravity and what it does but nobody ever saw it. The force of gravity makes a stone sink to the bottom of a pond. It pulls you down when you stumble and it makes a loose rock slide down a slope. It seems to reach up from deep inside the earth and it hugs us all to the surface of the globe. It reaches up, up above the ground getting gradually weaker and weaker as it reaches further and further out.

Scientists know all these things and a lot more about gravity. But nobody can explain what makes it. All we say is that it is there, built right into every speck of dust. Planets, moons and suns are made of materials called matter. So are rocks and water, clouds and specks of dust. And every speck of matter has a built in quota of gravity. A massive planet has more gravity than a little stone because it has more matter. The sun has even more built in gravity because it is more massive than, a planet.