Mass and Weight

Introduction

In everyday life, we often use the terms mass and weight as if they are the same. However, in physics, they are different quantities. Understanding the difference between mass and weight is very important.

Mass

Mass is the quantity of matter contained in a body.

It is a scalar quantity and does not depend on location.

The SI unit of mass is kilogram (kg).

Weight

Weight is the gravitational force acting on a body due to the Earth.

It is a vector quantity and always acts towards the center of the Earth.

Weight is given by:

W⃗ = m × g⃗

Here, W⃗ is weight, m is mass, and g⃗ is acceleration due to gravity.

Explanation

Mass remains constant everywhere because it does not depend on gravity. But weight depends on the value of g⃗, which can change from place to place.

  • Mass of a body is the same on Earth, Moon, or in space.
  • Weight of a body changes depending on gravitational acceleration.

For example, on the Moon, the value of g⃗ is smaller than on Earth, so weight becomes less.

Relation Between Mass and Weight

Weight is directly proportional to mass:

W⃗ = m × g⃗

If mass increases, weight also increases.

Difference Between Mass and Weight

  • Mass is the amount of matter in a body, while weight is the force acting on it.
  • Mass is a scalar quantity, while weight is a vector quantity.
  • Mass remains constant everywhere, while weight changes with location.
  • Unit of mass is kilogram (kg), while unit of weight is newton (N).

Examples from Daily Life

  • An astronaut has the same mass on Earth and Moon but less weight on the Moon.
  • A weighing machine measures weight but is calibrated to show mass.
  • A body in free fall feels weightless because no normal force acts on it.

Illustration

Earth W⃗

The weight W⃗acts vertically downward towards the center of the Earth.

Important Points

  • Mass is constant everywhere.
  • Weight depends on gravitational acceleration.
  • W⃗ = m × g⃗
  • Weight is always directed towards the center of Earth.

Conclusion

Mass and weight are different physical quantities. Mass tells us how much matter a body has, while weight tells us the force acting on it due to gravity. Understanding this difference is important in physics.

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