Overview
This lecture explains the concepts of mass, weight, gravitational field strength, and how to calculate the weight of an object. It also covers key definitions and differences between mass and weight.
Mass and Its Properties
- Mass measures the amount of matter in an object.
- The unit of mass is the kilogram (kg).
- Mass is a scalar quantity (has magnitude but no direction).
- Mass does not change based on location (Earth, Moon, or space).
Weight and Gravitational Field Strength
- Weight is the force acting on an object due to gravity.
- The unit of weight is the Newton (N).
- Weight depends on location; it changes with gravity.
- At Earth's surface, gravitational field strength (g) is 9.8 N/kg.
- Gravitational field strength measures the force of gravity at a specific location.
Calculating Weight
- The equation for weight: weight (N) = mass (kg) × gravitational field strength (N/kg).
- The weight of a 1 kg object on Earth: 1 kg × 9.8 N/kg = 9.8 N.
- Weight is directly proportional to mass; doubling the mass doubles the weight.
- You may need to memorize the weight equation for exams.
Measuring Weight and Center of Mass
- A calibrated spring balance (Newton meter) measures weight.
- Gravitational field strength varies by location (e.g., Moon's g = 1.6 N/kg).
- The force of gravity (weight) acts at a single point called the center of mass.
- Center of mass is the point where an object's mass is considered to be concentrated.
Key Terms & Definitions
- Mass — The amount of matter in an object, measured in kilograms.
- Weight — The force on an object due to gravity, measured in Newtons.
- Gravitational Field Strength (g) — The gravity force per kilogram at a location, in N/kg.
- Scalar Quantity — A measurement with magnitude only, no direction.
- Vector Quantity — A measurement with both magnitude and direction.
- Center of Mass — The point where the mass of an object is concentrated and where gravity acts.
Action Items / Next Steps
- Memorize the weight calculation formula: weight = mass × gravitational field strength.
- Learn the definition of center of mass.
- Practice related problems in the revision workbook.