What law states that two or more masses attract each other?

The principle that two or more masses attract each other is encapsulated in the law of universal gravitation. This law, formulated by Sir Isaac Newton, states that every point mass attracts another point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them. This means that as the mass of either object increases, the gravitational force between them increases, and as the distance between them increases, the gravitational force decreases.

This law is foundational for understanding how celestial bodies interact in space and is crucial in fields such as astrophysics and cosmology. It explains not just the falling apple towards Earth, but also the orbits of planets around the sun and the motion of galaxies.

In contrast to this, the other concepts mentioned deal with different physical principles. Newton's first law pertains to the behavior of objects in motion or at rest, the conservation of mass deals with the mass remaining constant in isolated systems, and the law of inertia emphasizes the tendency of objects to resist changes in their state of motion. Therefore, the law of universal gravitation specifically addresses the attractive force between masses, making it the correct choice.