Mass vs. Weight

3.1 Mass versus Weight

• Definition of Mass

  • Mass is a measure of the amount of matter in an object. It quantifies how much substance is contained within the object.
  • Mass is typically measured in kilograms (kg).

• Characteristics of Mass

  • Mass remains constant regardless of location.
  • The mass of an object does not change whether it is on Earth, the Moon, or in space.

• Definition of Weight

  • Weight is defined as the force exerted by gravity on an object.
  • Weight can be calculated using the formula:
    W = mg
    where:
  • W is the weight,
  • m is the mass (in kg),
  • g is the acceleration due to gravity (in m/s²).
  • Weight is a vector quantity and is affected by the local gravitational field strength.

• Effect of Gravity on Weight

  • On Earth, the standard gravitational field strength is approximately g ext{ } ext{(Earth)} = 9.81 ext{ m/s}^2 .
  • On the Moon, the gravitational field strength is approximately g ext{ } ext{(Moon)} = 1.62 ext{ m/s}^2 .

• Example Calculation

  • If an object has a mass of 2.0 kilograms:
  • Weight on Earth:
    W_{ ext{Earth}} = m imes g ext{(Earth)}
    W_{ ext{Earth}} = 2.0 ext{ kg} imes 9.81 ext{ m/s}^2 = 19.62 ext{ N}
  • Weight on the Moon:
    W_{ ext{Moon}} = m imes g ext{(Moon)}
    W_{ ext{Moon}} = 2.0 ext{ kg} imes 1.62 ext{ m/s}^2 = 3.24 ext{ N} .

• Conclusion

  • Thus, an object's mass is consistent and is a property that does not change with location, while its weight varies depending on the local gravitational field strength.