Table of Contents
Weight vs Mass
Mass is the amount of matter in an object and is constant everywhere. Weight is the gravitational force acting on that mass and depends on the local gravitational acceleration. A person with 70 kg of mass weighs 686.7 N on Earth but only 113.4 N on the Moon, even though the mass remains 70 kg in both locations.
Understanding weight on other planets is important for space mission planning, habitat design, and understanding how astronauts function in different gravitational environments. Low gravity affects bone density, muscle mass, fluid distribution, and physical capabilities.
Formula
Where W is weight (N), m is mass (kg), and g is surface gravitational acceleration (m/s²). Earth's g = 9.81 m/s². For each body: g = GM/r², where G is the gravitational constant, M is the body's mass, and r is its radius.
Surface Gravity Comparison
| Body | g (m/s²) | Ratio to Earth | 70 kg Weight (N) |
|---|---|---|---|
| Mercury | 3.70 | 0.38 | 259.0 |
| Venus | 8.87 | 0.90 | 620.9 |
| Earth | 9.81 | 1.00 | 686.7 |
| Moon | 1.62 | 0.17 | 113.4 |
| Mars | 3.72 | 0.38 | 260.4 |
| Jupiter | 24.79 | 2.53 | 1735.3 |
Frequently Asked Questions
Would I weigh more on Jupiter?
Yes, about 2.53 times more. A 70 kg person would weigh 1,735 N (390 lbf) on Jupiter. Every movement would require 2.5 times the force used on Earth, making it extremely difficult to stand or walk.
Why is Moon gravity so low?
The Moon has only 1.2% of Earth's mass and 27% of its radius. The smaller mass dominates the g = GM/r² equation, giving only about 1/6 of Earth's gravity.
Is there gravity in space?
Yes. Astronauts on the ISS experience about 90% of Earth's gravity. They appear weightless because they are in continuous free fall (orbiting), not because gravity is absent.