Why do planets orbit the sun instead of drifting away?

Planets orbit the sun because of gravity. The sun's enormous mass creates a gravitational pull that constantly attracts planets toward it. However, planets also have sideways velocity from when the solar system formed out of a spinning cloud of gas and dust. This combination of inward gravitational pull and sideways momentum creates a stable orbit, where the planet perpetually falls toward the sun but keeps missing it because of its lateral speed. If a planet moved too slowly, gravity would pull it into the sun. If it moved too fast, it would escape into space. At just the right speed, the two forces balance, producing an elliptical orbit that keeps the planet circling the sun indefinitely without drifting away or falling in.