Mass and Weight

Summary and Exam Tips for Mass and Weight

Mass and Weight is a subtopic of Motion, forces, and energy, which falls under the subject Science in the IB MYP curriculum. Mass is a fundamental property of matter that resists changes in motion, known as inertia, and is measured in kilograms (kg). It remains constant regardless of location. Weight, on the other hand, is the gravitational force acting on a mass and is measured in newtons (N). The formula to calculate weight is $W = mg$, where $g$ is the gravitational field strength, approximately 9.8 N/kg on Earth. Weight varies with changes in gravitational field strength, as seen in different celestial bodies like the Moon or Jupiter. A balance can be used to compare weights and hence masses, though mass remains constant while weight changes with gravity. Understanding the distinction between mass and weight is crucial, as mass is a scalar quantity and weight is a vector quantity. Practical applications include understanding how an astronaut's weight changes in different gravitational fields while their mass remains constant, and how scales measure weight to determine mass.

Exam Tips

• Understand Key Concepts: Ensure you can distinguish between mass and weight. Remember, mass is constant, while weight varies with gravitational field strength.
• Formula Familiarity: Be comfortable using the formula $W = mg$ to calculate weight, and know the typical value of $g$ on Earth.
• Practical Applications: Relate theoretical concepts to real-world examples, such as how an astronaut's weight changes in space.
• Use of Balances: Know how balances work to compare weights and understand that they measure weight to infer mass.
• Gravitational Field Strength: Remember that $g$ is both the gravitational force per unit mass and the acceleration due to gravity.