Isaac Newton imagined firing a cannonball sideways from a tall mountain, faster and faster each time. Where does it land? Launched fast enough, he realized, it never lands at all.
From the circular-motion topic: anything moving in a circle needs a centripetal force — a net force toward the circle's center. The Moon circles Earth, so something must supply that force. Earth's gravitational force on the Moon points straight at Earth's center — exactly the direction a centripetal force needs.
So why does the Moon never hit Earth? As the Moon falls toward Earth, its sideways motion carries it onward — and Earth's surface curves away beneath it. The fall and the curve match exactly, so the Moon falls around Earth instead of into it.
Every orbit works this way — the Moon around Earth, satellites around Earth, Earth around the Sun.
A weather satellite circles Earth. Which force supplies its centripetal force?
Viktor says the weather satellite is continually falling toward Earth. Is he correct?
Esme says a satellite must keep its engines firing to stay in orbit. Is she correct?
An orbiting satellite is always falling toward Earth. Why does it never reach the ground?
Suppose Earth's pull on an orbiting probe suddenly vanished. What would the probe do next?
A mapping probe circles Mars with its engines off. What keeps it moving in its circle?