Introduction

The universal law of gravitation was put forth by Sir Isaac Newton in 1687. The inspiration to develop the law came to Isaac Newton after he saw an apple fall from a tree. This article will discuss the weight and the gravitational force, universality of gravity, and gravitational constant.

The universal law of gravitation

• The SI unit of G (gravity) is N m2 Kg-2.
• Henry Cavendish, an 18th century scientist, found the value of G by using the sensitive balance. The value of G is 6.673 x 10-11 N m2 Kg-2.
• According to Newton’s universal law of gravitation, a force along a line joins every particle in the universe to every other article.
• This force that attracts these particles is inversely proportional to the square of the distance between the particles and is directly proportionate to the product of their masses.
• The universal law of the gravitation equation is

F = G m1m2r2

In the above equation, F is the magnitude of the gravitational force, G is the gravitational constant. The gravitational constant refers to the same gravitational force of all celestial bodies in the universe.

• While Newton might have been the first scientist to propose a mathematical form for gravitation, philosopher Galileo Galilei and his contemporaries were also trying to understand and explain the existence of a force that caused the motion of planets.

Universality of gravity

• Newton’s universal law of gravitation extends beyond the Earth’s gravitational force and is about the universality of gravity. Therefore, the law of gravity applies to all bodies, big and small, celestial or terrestrial. The approximate value of G is 6.673 10-11 N m2 Kg-2.

Weight and the gravitational force

• The gravitational field is a model or concept that is used to explain the influences of a massive body on producing a force on another massive body. The gravitational field is measured in newtons per kilogram.
• It is observed that every object with mass has its gravitational field. Therefore, every matter with mass exerts a force that attracts other objects. The relationship between mass and the gravitational field is directly proportional. Hence, the gravitational force is greater when there is more mass. For example, since the Earth has a greater mass than the moon, it has a greater gravitational field than the moon.
• The gravitational force of an object can be calculated by –

Gravity force = mass   gravitational field strength

• The gravitational field inside a hollow spherical will be zero.
• The gravitational field strength of planet Earth is 10 N/kg.
• Weight refers to the force exerted on an object due to the gravitational attraction between the Earth and the object.
• While weight is not the same as mass, the relationship between weight and mass is directly proportional; therefore, for given gravitational field strength, if the mass of the object is greater, then the object’s weight is also greater.
• Weight is considered a non-contact force because an object doesn’t need to touch the Earth to have a weight. Therefore, weight is a non-contact force because gravity can exert its force even through a field.
• With the help of a Newton meter, which is a calibrated spring balance, the weight of an object can be measured.
• Since the weight of an object is also referred to as gravity force, therefore, the equation to measure gravity force is

Gravity force (weight) = mass   gravitational field strength

Conclusion

From the above article, we learned about the law of gravitation. This universal law of gravitation is applicable for all bodies, big and small, celestial or terrestrial.  Also described gravitation constant  G and its value.