Weight — Science definition
The force of gravity on an object's mass, calculated as weight = mass × g (W = mg).
Where it is taught
- Gravity & Friction — Forces, Physical Science: Matter, Forces & Energy, Grade 8
In use
A heavier object has greater weight but also greater inertia, giving the same ideal acceleration.
Gravity & Friction
Questions using weight
Problem 1
Find the weight of a 50 kg student on Earth. Use g = 9.8 m/s² and W = mg.
Answer and explanation
490 N
W = mg = 50 × 9.8 = 490 N.
Problem 2
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 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.