Study Notes
Mass is a measure of the amount of matter in an object and remains constant regardless of location, while weight is the gravitational force acting on that mass and can vary depending on the gravitational field strength.
- Mass — Measure of matter in an object; resists change in motion (inertia). Example: An astronaut's mass remains the same on Earth and the Moon.
- Weight — Gravitational force on a mass. Example: A 100 kg person weighs 980 N on Earth but only 160 N on the Moon.
- Gravitational Field Strength (g) — Force per unit mass in a gravitational field. Example: On Earth, g is approximately 9.8 N/kg.
- Mass vs. Weight — Mass is a constant, scalar quantity; weight is a variable, vector quantity affected by gravity. Example: A balance shows equal mass on Earth but not on the Moon.
Exam Tips
Key Definitions to Remember
- Mass: Measure of matter in an object; resists change in motion.
- Weight: Gravitational force on a mass.
- Gravitational Field Strength: Force per unit mass in a gravitational field.
Common Confusions
- Confusing mass with weight, as they are different properties.
- Assuming weight is constant like mass.
Typical Exam Questions
- What is the weight of an 80 kg astronaut on a planet with g = 3.8 N/kg? Answer: 304 N
- How does the weight of a space probe on Mars compare to its weight on Earth? Answer: Decreased
- Which statement about mass is correct? Answer: It resists any change in motion of the object.
What Examiners Usually Test
- Understanding the difference between mass and weight.
- Ability to calculate weight using W = mg.
- Knowledge of how gravitational field strength affects weight.