gravitational force

Meaning: Gravitational force is the attractive force between any two objects that have mass. It acts along the line joining their centers and weakens with the square of the distance. The pair of forces is equal in magnitude and opposite in direction (Newton's third law), even when the masses differ. Near Earth's surface, the gravitational force on an object is its weight, mg, with g ≈ 9.8 m/s².

Equation: F = Gm₁m₂/r², where F is the magnitude of the force (N), G is the universal gravitational constant, 6.67 × 10⁻¹¹ N·m²/kg², m₁ and m₂ are the masses (kg), and r is the center-to-center distance (m).

On the MCAT: Expect ratio questions: doubling r cuts F to one-fourth; doubling one mass doubles F. In circular orbits, gravity supplies the centripetal force, so GMm/r² = mv²/r and v = √(GM/r). Coulomb's law has the same inverse-square form, so passages may ask you to compare the two.

Common confusion: A larger mass does not feel a larger force. Both objects feel the same magnitude, but the smaller mass accelerates more (a = F/m). Also, r is measured center to center, not as height above the surface, and G (a universal constant) is not g (the local free-fall acceleration).