--- 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: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # 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 is the amount of matter in an object, measured in grams (g) or kilograms (kg). Weight is gravity's pull on that matter, measured in newtons (N). A change of world or gravity alone does not change mass. Adding matter increases mass: adding 1 kg to a 6 kg sample gives 7 kg. Removing matter reduces mass. If no matter is added or removed, the same object keeps its mass while its weight can change with gravity. *(drawing: The same 4 kg rock on three worlds. Bars show weight in newtons, using rounded field strengths. Its mass stays 4 kg.)* **Example.** Sam packs a bag with a mass of 5 kg. On Earth, gravitational field strength is g = 10 N/kg. Use weight = mass x g = 5 x 10 = 50 N to find the bag's weight. 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.** Check what each unit measures. Grams (g) and kilograms (kg) measure mass. Newtons (N) measure forces, including weight. N/kg measures gravitational field strength. To calculate weight with weight = mass x g, use mass in kg and g in N/kg. For a decimal mass on Earth, multiplying by 10 makes each digit worth ten times as much: 2.4 kg weighs 24 N. On the Moon, g is about 1.6 N/kg. Since 1.6 is 16 tenths, multiply mass by 16, then divide by 10. Sam's 5 kg bag weighs (5 x 16) / 10 = 80 / 10 = 8 N. Always use g for the place in the question. To find mass from weight, divide by g. When g is 1.6 N/kg, multiply both numbers in the division by 10 to make the divisor a whole number. A box weighing 19.2 N on the Moon has mass 19.2 / 1.6 = 192 / 16. Since 16 x 12 = 192, its mass is 12 kg. Check by multiplying: 12 x 1.6 = 19.2 N. **Recap.** Mass (kg) measures matter and stays the same when none is added or removed. Weight (N) is gravity's pull: weight = mass x g. *The mass-and-weight teaching, worked calculations and scenes were written for this dataset. The explanations about adding and removing matter and the revised assessment questions were also written for this dataset.* ## 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)