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Mass is measured in kilograms and quantifies inertia. Gravitational weight is a force, W = mg, measured in newtons. A scale’s support-force reading can differ from gravitational weight.
By Matan · Updated
Three quantities to keep apart
| Quantity | Meaning | Unit |
|---|---|---|
| Mass | Inertial property of the body | kg |
| Gravitational weight | Local gravitational force | N |
| Apparent weight | Specified support-force reading | N |
A body moved to a different gravitational field keeps the same mass if its physical state and contents are otherwise unchanged. Weight changes with local g. [1]
Worked field comparison
A 10 kg object has weight 98 N where g = 9.8 m/s² and 16 N where g = 1.6 m/s². These are stated rounded field values. Applying a 20 N net horizontal force to the same object gives 2.0 m/s² acceleration in either ideal comparison.
Why an elevator changes the reading
For upward acceleration a, a horizontal scale reads N = m(g + a). A 10 kg object accelerating upward at 1.0 m/s² gives 108 N at g = 9.8, although its gravitational weight is still 98 N. Constant upward velocity alone does not produce that increase.
Floating is not masslessness
Orbiting astronauts and their spacecraft fall together under gravity, so support forces can be small. They still have mass and gravitational acceleration. A kilogram display usually converts measured force using a calibration; it does not erase the distinction.
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How this article was checked
Sources checked; calculations checked where shown. The definitions, model assumptions and main explanatory claims were cross-checked against the sources below. Worked-example arithmetic and units were checked separately. These examples are illustrative calculations, not experimental measurements.
Source cross-check and editing assisted by AI. No independent human scientific review is recorded for this revision. The check applies to the version dated 10 September 2026; it is not a guarantee that every possible interpretation is correct.
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Sources and further reading
- OpenStax: Weight and support forces — Weight and support forces.
- OpenStax: Elevator force balance — Elevator force balance.
Cite this article
Matan. “Mass vs. Weight: Not the Same Thing.” Your Physicist. Originally published 2026-06-11; updated 2026-09-10. https://your-physicist.com/mass-vs-weight-not-the-same-thing/
Revision history
: Separated gravitational and apparent weight with a table and checked field and scale examples. Added linked sources and a transparent verification record.
