The gravitational force between objects depends on their mass and the distance between them. While it is true that all matter contributes to the gravitational force, the gravitational force between small objects, such as individual molecules, is extremely weak compared to other forces at play.
The gravitational force is described by Newton's law of universal gravitation, which states that the force is directly proportional to the product of the masses of the two objects and inversely proportional to the square of the distance between them. However, the gravitational force is an extremely weak force compared to other fundamental forces, such as electromagnetic forces or nuclear forces.
For example, the electromagnetic forces between molecules, atoms, and subatomic particles are many orders of magnitude stronger than gravitational forces. In everyday situations, electromagnetic forces dominate interactions between molecules and determine the behavior of matter on a macroscopic scale.
In addition, the effect of gravity is generally negligible at the molecular level because the masses of individual molecules are extremely small compared to macroscopic objects. The gravitational force between individual molecules is so tiny that it is typically dwarfed by other forces acting on them.
Furthermore, the distance over which the gravitational force acts is limited. The force decreases rapidly with distance, and on the molecular scale, the distances involved are typically very small, making the gravitational force even weaker and harder to detect or measure accurately.
In summary, while all matter does contribute to the gravitational force, the gravitational effects at the scale of individual molecules are typically too weak to be practically measured or identified. Other forces, such as electromagnetic forces, play a dominant role in the behavior and interactions of molecules on smaller scales.