Gravity is the fundamental force of attraction that exists between any two objects possessing mass. On Earth, it is the invisible pull that keeps everything, from oceans to people, grounded. Does gravity change with altitude? Yes, Earth’s gravitational pull varies with altitude, though the change is often smaller than expected in daily life.
How Altitude Influences Gravity
Gravity weakens as the distance between two objects increases, a principle directly applicable to Earth’s gravity and altitude. As one ascends, they move further from Earth’s center of mass, where the planet’s gravitational pull originates. Isaac Newton’s law of universal gravitation states that gravitational force is inversely proportional to the square of the distance between two masses. This means if the distance from Earth’s center were to double, the gravitational force would become four times weaker.
For typical human altitudes, such as mountain peaks or airplanes, the change in gravity is very small. At sea level, acceleration due to gravity is approximately 9.81 meters per second squared. Climbing Mount Everest (8,848 meters above sea level) reduces this to around 9.773 meters per second squared, a decrease of roughly 0.03% per kilometer of ascent. Even at the International Space Station (400 kilometers above Earth), gravity is still nearly 90% as strong as on the surface; astronauts experience weightlessness because they are continuously falling around the Earth, not because gravity is absent.
Other Factors Affecting Gravity
Beyond altitude, other Earth characteristics subtly affect local gravity. Earth is an oblate spheroid, bulging at the equator and flattened at the poles. Consequently, locations at the poles are marginally closer to Earth’s center than those at the equator, resulting in slightly stronger gravity at the poles (around 9.832 m/s²) compared to the equator (approximately 9.780 m/s²).
Earth’s rotation also affects perceived gravity. The planet’s spin generates centrifugal force, acting outward and subtly counteracting gravity. This effect is most pronounced at the equator, where rotational speed is highest, reducing apparent gravity by up to 0.3%. The combined effect of Earth’s shape and rotation contributes to a total global gravity variation of about 0.7%.
Local geological variations also contribute to minor gravity differences. Dense rock formations beneath the surface, like mineral deposits, can cause a slightly stronger local gravitational field, while less dense sedimentary rocks result in a weaker pull. These anomalies, influenced by topography and subsurface density, are generally imperceptible.
The Practical Significance of Gravity Changes
For most everyday activities, gravity variations due to altitude or other factors are negligible. People do not feel lighter or experience significant weight changes on a mountain or in an airplane; differences are too minute without specialized equipment.
However, these subtle gravitational changes are significant for sensitive scientific instruments and advanced technologies. Fields like geodesy, which measures Earth’s shape, orientation, and gravity, rely on understanding these variations for precise measurements. Satellite navigation systems, such as GPS, incorporate detailed gravitational models for accurate positioning. Geophysicists also use gravity anomalies to map Earth’s interior, detect density variations, and aid in resource exploration.