By Kevin Lee, updated Mar 24, 2022
When you ask a child what gravity does, most will say it makes things fall. To help them understand the invisible force that pulls everything together, we’ll break the concept down into everyday ideas and proven science.
Every object has a mass—the amount of matter it contains. Mass never changes unless the object moves near the speed of light. The more mass an object has, the stronger its gravitational pull. That’s why Jupiter, the largest planet, pulls harder on surrounding bodies than the tiny Moon does.
Weight is the force you feel when an object is pulled toward a planet. Because Earth’s gravity is stronger than the Moon’s, you weigh more here than you would on the lunar surface. Density also matters: Saturn is almost 100 times heavier than Earth, but because it’s largely gas and has a lower density, a person would weigh about the same on Saturn as on Earth.
Show a scale model of the solar system and point out the Sun at its center. Explain that the Sun’s immense mass creates a powerful gravitational field that keeps the planets in orbit. If the Sun were to vanish, the planets would drift away in straight lines instead of staying bound by gravity.
Describe how satellites orbit Earth just as Earth orbits the Sun. The International Space Station orbits at about 400 km above the surface, constantly “falling” toward Earth while its forward speed keeps it from crashing. The Moon follows a similar path, completing a 27‑day orbit and contributing to ocean tides through its own gravitational pull.
Gravity pulls objects toward Earth, but objects in orbit also move sideways at high speed. Think of spinning a toy around your head on a string: the string pulls the toy inward, while the toy’s forward motion keeps it from falling straight in. If you stop spinning, the toy will eventually fall. This balance between “pull” and “speed” explains why satellites stay in orbit.
Sir Isaac Newton showed that the gravitational force between two masses is inversely proportional to the square of the distance between their centers: F = G·(m₁m₂)/r². As a child climbs Mount Everest, the distance to Earth’s center increases, slightly reducing gravity; sensitive scales can detect this minute change.
Drop a small ball from a tall building and watch it accelerate at 9.8 m/s². This constant rate of acceleration demonstrates that all objects fall at the same speed when air resistance is negligible.
Finally, remember Voyager 1—launched in 1977—has already escaped Earth’s gravitational pull, traveling beyond our solar system. It’s a tangible example that objects can leave a planet’s gravity under the right conditions.
