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Physics · Grades 6–10

Mass, weight and gravitational field

Separate an object's mass from the local gravitational force.

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Learn the idea

Mass

Mass is a property measured in kilograms in SI. It does not become a force when an object is on another world.

Weight

Weight is the gravitational force, calculated as mg when a local field strength g is specified.

Field strength

N/kg and m/s² are equivalent units for the same local gravitational parameter.

Near-surface model

Treating g as constant is an approximation over a limited region, not a statement about every altitude.

Worked examples

A 6 kg mass is in a field of 10 N/kg. Find weight.

W = mg = 6 × 10 = 60 N.

60 N

Which SI unit is used for mass?

Kilogram measures mass; newton measures force.

kg

Check your understanding

  1. A mass weighs 32 N in a field of 8 N/kg. Find mass.

  2. If an unchanged object moves to a weaker gravitational field, what usually changes?

    1. Its mass necessarily
    2. Its number of protons necessarily
    3. Its weight

  3. Explain why 60 kg is not a correctly stated weight in an SI force calculation.

Answers and marking notes

Answers and marking notes
  1. 4 kg

    m = W/g = 32/8 = 4 kg.

  2. Its weight

    Weight depends on field strength while the object's mass can remain the same.

  3. Kilograms measure mass; weight as a force should be given in newtons.

    Credit the units distinction without criticizing everyday language outside the calculation.

Further reading and review references

These are reference links, not copied exercises, institutional endorsement or proof of independent review.

Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.