Study Notes
Mass is a property that opposes changes in motion and remains constant regardless of location, while weight is the gravitational force acting on a mass and varies with gravitational field strength.
- Mass — the amount of matter in an object, measured in kilograms (kg).
Example: A 50 kg person has the same mass on Earth and the Moon. - Weight — the force on a mass due to gravity, measured in newtons (N).
Example: A 50 kg person weighs 490 N on Earth (using g = 9.8 N/kg). - Gravitational Field Strength (g) — the force per unit mass in a gravitational field, measured in newtons per kilogram (N/kg).
Example: On Earth, g is approximately 9.8 N/kg. - Weight Equation — W = mg, where W is weight, m is mass, and g is gravitational field strength.
Example: A 100 kg object weighs 980 N on Earth.
Exam Tips
Key Definitions to Remember
- Mass is the amount of matter in an object, measured in kilograms.
- Weight is the gravitational force on a mass, measured in newtons.
- Gravitational field strength is the force per unit mass, measured in N/kg.
Common Confusions
- Confusing mass with weight; mass is constant, weight varies with gravity.
- Thinking weight is the same everywhere; it changes with gravitational field strength.
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 mass of an object change when moved from Earth to Mars? Answer: Mass remains unchanged.
- Which quantity is weight an example of? Answer: Force
What Examiners Usually Test
- Understanding the difference between mass and weight.
- Ability to use the formula W = mg to calculate weight.
- Knowledge of how weight changes with different gravitational fields.