Mass — Science definition
The amount of matter in an object, measured in kilograms; it doesn't change no matter where the object is.
Where it is taught
- Gravity & Friction — Forces, Physical Science: Matter, Forces & Energy, Grade 8
In use
Gravity is an attractive interaction between objects with mass.
Gravity & Friction
Questions using mass
Problem 1
A rock has a mass of 12 kg. What is its weight on Earth? (g = 9.8 m/s²)
Answer and explanation
117.6 N
W = mg = 12 × 9.8 = 117.6 N.
Problem 2
An object weighs 98 N on Earth. Using W = mg with g = 9.8 m/s², find its mass.
Answer and explanation
10 kg
m = W ÷ g = 98 ÷ 9.8 = 10 kg.
Problem 3
Using g≈10 N/kg, find the weight of a 3 kg object and explain why its mass stays the same on the Moon. Explain the reasoning in your own words.
Answer and explanation
30 N on Earth; the same 3 kg mass has a smaller weight on the Moon.
Weight near Earth is 3×10=30 N.
A different gravitational field changes force, but not the object's amount of matter or inertia.
Response criteria
- Use the stated conditions.
- Show the evidence or calculation.
- Explain the conclusion and any stated limitation.
Problem 4
An object of mass 3 kg has weight 30 N in a simplified g=10 N/kg model. Would its mass change on the Moon?
Hints
State what the supplied observations or conditions establish, and separate that from any assumption.
Answer and explanation
Mass remains 3 kg; weight changes with the local gravitational field.