How do planets stay in orbit around the sun?

Planets stay in orbit because of a balance between the sun's gravitational pull and the planet's forward momentum. Gravity constantly pulls the planet toward the sun, but the planet is also moving sideways at high speed. These two effects combine so that as the planet falls toward the sun, it also moves forward enough to keep curving around it rather than crashing into it. This is essentially what an orbit is: a continuous freefall where the object keeps missing its target. Isaac Newton first explained this mathematically, and Einstein later refined our understanding through general relativity, describing gravity as a curvature of spacetime that causes planets to follow curved paths called ellipses around the sun.