Table of Contents
Mass vs. Weight
Mass and weight are fundamentally different physical quantities that are often confused in everyday language. Mass is an intrinsic property of matter, measured in kilograms (kg), and remains constant regardless of location. Weight is the gravitational force acting on a mass, measured in Newtons (N), and changes depending on the gravitational field strength.
On Earth's surface, a 1 kg mass experiences a gravitational force of approximately 9.807 Newtons. On the Moon, the same 1 kg mass weighs only about 1.625 Newtons because the Moon's gravitational acceleration is about one-sixth that of Earth. The mass, however, remains 1 kg in both locations.
Conversion Formula
The standard value of gravitational acceleration g = 9.80665 m/s^2 is defined by international agreement and represents the average value at sea level at 45 degrees latitude.
Quick Reference Table
| Mass (kg) | Force (N) | Force (lbf) | Force (kgf) |
|---|---|---|---|
| 1 | 9.807 | 2.205 | 1.000 |
| 5 | 49.03 | 11.02 | 5.000 |
| 10 | 98.07 | 22.05 | 10.00 |
| 50 | 490.3 | 110.2 | 50.00 |
| 100 | 980.7 | 220.5 | 100.0 |
| 1000 | 9807 | 2205 | 1000 |
Gravity on Different Celestial Bodies
| Body | g (m/s²) | Relative to Earth |
|---|---|---|
| Earth | 9.807 | 1.00 |
| Moon | 1.625 | 0.166 |
| Mars | 3.721 | 0.379 |
| Jupiter | 24.79 | 2.528 |
| Venus | 8.87 | 0.905 |
Frequently Asked Questions
Is 1 kg equal to 9.8 Newtons?
A mass of 1 kg on Earth's surface experiences a gravitational force (weight) of approximately 9.807 N. However, 1 kg is not "equal to" 9.8 N because they measure different things: mass vs. force. The conversion depends on the gravitational acceleration at the location.
What is the difference between N and kgf?
The Newton (N) is the SI unit of force. The kilogram-force (kgf) is a non-SI unit defined as the force exerted by 1 kg under standard gravity (9.80665 m/s^2). So 1 kgf = 9.80665 N. The kgf is still used in some engineering contexts but is not recommended in scientific work.
Why does g vary on Earth?
Gravitational acceleration varies from about 9.78 m/s^2 at the equator to 9.83 m/s^2 at the poles due to Earth's oblate shape and centrifugal effects from rotation. Altitude also matters: g decreases by about 0.003 m/s^2 per 1000 meters of elevation above sea level.