Table of Contents
Gravitational Acceleration Explained
Gravitational acceleration is the acceleration experienced by an object due to the gravitational force of a massive body. On Earth's surface, this is approximately 9.80665 m/s² (standard gravity, 1g). Gravity varies with altitude, latitude, and the mass distribution of the body. Objects on mountaintops experience slightly less gravity than at sea level.
This concept is fundamental to orbital mechanics, satellite engineering, and planetary science. Understanding how gravity changes with distance allows us to calculate satellite orbits, predict tides, and design spacecraft trajectories.
Newton's Law of Gravitation
Where G is the gravitational constant (6.674 × 10-11 N m²/kg²), M is the mass of the body, and r is the distance from the center. The escape velocity is the minimum speed needed to leave the gravitational field.
Gravity on Different Bodies
| Body | Surface g (m/s²) | Relative to Earth | Escape Velocity |
|---|---|---|---|
| Earth | 9.81 | 1.00 | 11.2 km/s |
| Moon | 1.62 | 0.17 | 2.4 km/s |
| Mars | 3.72 | 0.38 | 5.0 km/s |
| Jupiter | 24.79 | 2.53 | 59.5 km/s |
| Venus | 8.87 | 0.90 | 10.4 km/s |
Frequently Asked Questions
Does gravity change with altitude?
Yes. Gravity decreases with the square of the distance from the center. At the ISS orbit (400 km), gravity is about 88% of surface gravity. Astronauts experience weightlessness because they are in free fall, not because gravity is absent.
Why is gravity different at poles vs. equator?
Earth is an oblate spheroid wider at the equator by about 21 km, so the surface is farther from the center there. Additionally, Earth's rotation creates a centrifugal effect reducing apparent gravity at the equator. The net difference is about 0.5% between poles (9.832) and equator (9.780).
What is the gravitational constant G?
G is the universal gravitational constant equal to 6.674 × 10-11 N m²/kg². It was first measured by Henry Cavendish in 1798 and remains one of the most difficult physical constants to measure precisely because gravitational forces between laboratory-scale objects are extremely weak.