Gravity vs Weight
Gravity and weight are two concepts involved in the gravitational field theory of physics. These two concepts are often misinterpreted and used in the wrong context. It is vital to have a better and correct understanding of gravity and weight, if one is to excel in science. These two are almost similar concepts that are used interchangeably. However, we will see here, that gravity and weight are not the same. In this article, we are going to discuss what gravity and weight are, their basic concepts, applications, similarities and finally their differences.
Gravity is the common name given to the gravitational field. Gravitational field is a concept and a method for calculating and explaining phenomena happening around any object with a mass. A gravitational field is defined around any mass. According to Newton’s universal law of gravitation two masses M and m separated by a finite distance r exerts a force F = G M m / r2 on each other. The gravitational field intensity of a point located at a distance r from the mass is defined as the force per unit mass on the point r; this is commonly termed as g, where g= GM/r2. Since we know F = ma and F = GMm/r2, we can see that a = GM/r2. That means the gravitational field intensity and the acceleration due to the gravitational force are the same. The gravitational field intensity is measured in meters per seconds squared.
Weight is defined as the force on a mass due to the gravitational field of another object. Since weight is a force, it’s measured in Newton. However, day to day usage of the term “weight” is often used in the context of “mass”. The unit for measuring mass is kilograms, however, in daily usage the weight is measured in kilograms. This is a misinterpretation. Since the definition of the weight is the force due to the gravitational field, it is equal to the product of the mass and the gravitational acceleration at that point (W = m g). But, the mass of the object is a fixed value. Therefore, the same object would give two weights in different altitudes, since the gravitational acceleration is different. This also explains the weightlessness on a free fall. There is gravity acting on the body, however, there is no force to balance the static condition. Therefore, a free fall will cause the feeling of weightlessness.
What is the difference between Gravity and Weight?
• Gravity, or if more properly defined, gravitational field is a concept used to describe phenomena taking place around a mass, the weight is the force due to gravity.
• The gravitational field intensity at a point is the gravitational acceleration of the mass. It does not depend on the test mass. The weight of an object depends on that object and the gravitational field.
• Weight is a force, therefore, it is a vector, while gravity is a concept. However, the gravitational field intensity at a certain field is a vector, while the gravitational field intensity over the space is a vector field.