Echoes Within

🌍 Gravity and Weight of a Body

🔹 Introduction to Gravity

Gravity is the natural force of attraction between any two objects that have mass. Sir Isaac Newton first explained this force through his Universal Law of Gravitation.

• Every object in the universe attracts every other object with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

• On Earth, this force of attraction pulls all objects toward its center, which we commonly call the force of gravity.

This force is responsible for holding our atmosphere, causing objects to fall, and keeping planets in their orbits.

🔹 Definition of Weight

The weight of a body is the force with which the Earth attracts it toward its center due to gravity.

• Weight is a force, not a constant property of a body.

• It depends on the mass of the body (m) and the acceleration due to gravity (g).

Mathematically,

W=mg

Where:

• W = Weight of the body (in Newton, N)

• m = Mass of the body (in kilograms, kg)

• g = Acceleration due to gravity (9.8 m/s2 near Earth’s surface)

🔹 Example Calculation

Suppose the mass of a stone is 5 kg.
Its weight on the Earth’s surface will be:

W=mg=5×9.8=49 N

So, the stone experiences a downward force (weight) of 49 Newtons.

🔹 Important Points

1. Mass vs Weight

   • Mass is constant everywhere; weight changes with location because $g$ changes.

   • Example: A 60 kg person has the same mass on Earth and the Moon, but their weight will be much less on the Moon since $g$ is smaller.

2. Unit

   • Mass: kilogram (kg)

   • Weight: Newton (N)

✅ Conclusion:
Gravity is the universal force of attraction that gives rise to the weight of a body. The weight is simply the gravitational pull of the Earth on that body and can be calculated using W=mg.