---
title: "Mass vs Weight"
description: "Distinguish between mass (amount of matter, measured in kg) and weight (gravitational force, measured in N), use the equation weight = mass × gravitational field strength, and explain why g differs on"
canonical: https://lightmysky.com/learn/science/mass-vs-weight-mt_sUVeVXzRuq
source: https://lightmysky.com/learn/science/mass-vs-weight-mt_sUVeVXzRuq.md
retrieved: 2026-10-19
---

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# Mass vs Weight

Distinguish between mass (amount of matter, measured in kg) and weight (gravitational force, measured in N), use the equation weight = mass × gravitational field strength, and explain why g differs on other planets and stars

Subject: Science · Area: Forces & Motion · Ages 11 to 12
Page: https://lightmysky.com/learn/science/mass-vs-weight-mt_sUVeVXzRuq

## Ready when they can

- Explains the difference between mass and weight with correct units for each
- Calculates weight using W = mg with g = 10 N/kg on Earth
- Predicts what would happen to an object's weight on the Moon or Jupiter
- Explains why mass stays constant but weight changes in different gravitational fields

## Lesson: Mass vs weight

Mass and weight sound alike, but they are not the same thing. Mass is the amount of matter (stuff) packed into something, measured in kilograms (kg). Weight is the pull of gravity on that mass, measured in newtons (N). Your mass never changes, no matter where you go. Your weight does change, because it depends on how strong gravity is around you.

*(drawing: Same rock, same 10 kg mass everywhere. The weight changes because each place pulls with a different strength of gravity.)*

**Example.** Sam packs a bag with a mass of 5 kg. On Earth, gravitational field strength is g = 10 N/kg, so the bag's weight is weight = mass x g = 5 x 10 = 50 N. If the bag's mass stayed exactly the same but it travelled to the Moon, where g is about 1.6 N/kg, its weight would drop to 5 x 1.6 = 8 N.

Read g as newtons per kilogram. On Earth, g = 10 N/kg means each kilogram is pulled with 10 newtons. To work backwards, divide: mass = weight / g. A crate weighing 120 N on Earth has a mass of 120 / 10 = 12 kg.

**Tip.** Use the units to check yourself. Kilograms (kg) always mean mass. Newtons (N) always mean weight. If a question gives you kg and asks for N, multiply by g.

**Recap.** Mass (kg) is fixed and measures how much matter you have. Weight (N) is a force that changes with gravity, found using weight = mass x g.

## Practice

28 questions on this page, each with its working shown.

## Needs first

- [Gravity & Falling Objects](https://lightmysky.com/learn/science/gravity-and-falling-objects-mt_AvrQauS_zX)

## Opens up

- [Terminal Velocity](https://lightmysky.com/learn/science/terminal-velocity-mt_3eNYHV-m-c)
- [Universal Gravitation](https://lightmysky.com/learn/science/universal-gravitation-mt_oLjz18CxDg)
- [Newton's First & Second Laws](https://lightmysky.com/learn/science/newtons-first-and-second-laws-mt_tXxxCFl32J)