The correct option is **B. Gravitational forces are always attractive, while electrostatic forces can be either attractive or repulsive.** ### Detailed Explanation: 1. **Understanding the Forces:** - **Gravitational Forces:** These are the forces of attraction that exist between any two masses. The gravitational force is always attractive, meaning it pulls objects toward each other. This is described by Newton's Law of Universal Gravitation, which states that the force \( F \) between two masses \( m_1 \) and \( m_2 \) separated by a distance \( r \) is given by: \[ F = G \frac{m_1 m_2}{r^2} \] where \( G \) is the gravitational constant. Since both masses are always positive, the force is always attractive. - **Electrostatic Forces:** These forces arise from the interaction between charged particles. According to Coulomb's Law, the force \( F \) between two point charges \( q_1 \) and \( q_2 \) separated by a distance \( r \) is given by: \[ F = k \frac{|q_1 q_2|}{r^2} \] where \( k \) is Coulomb's constant. The key point here is that if the charges are of the same sign (both positive or both negative), the force is repulsive, pushing the charges apart. If the charges are of opposite signs, the force is attractive, pulling them together. 2. **Why Option B is Correct:** - Option B correctly identifies that gravitational forces are always attractive due to the nature of mass, while electrostatic forces can be either attractive or repulsive depending on the types of charges involved. This fundamental difference is crucial in understanding how these forces operate in various physical situations. ### Why the Other Options are Incorrect: - **Option A: Electrostatic forces can act over much larger distances than gravitational forces.** - This statement is incorrect. In fact, gravitational forces can act over very large distances, such as between planets and stars, and they do not diminish as quickly as electrostatic forces. While both forces decrease with distance, gravitational forces have a much longer range due to their always attractive nature and the fact that they act on mass, which is ubiquitous. - **Option C: Electrostatic forces have a much weaker strength than gravitational forces at all distances.** - This is also incorrect. Electrostatic forces are generally much stronger than gravitational forces at the atomic and molecular levels. For example, the electrostatic force between two electrons is significantly stronger than the gravitational force between them. The strength of electrostatic forces can be orders of magnitude greater than gravitational forces, especially at small distances. - **Option D: Gravitational forces can change with the charge of the objects involved, whereas electrostatic forces do not depend on mass.** - This statement is misleading. Gravitational forces depend solely on mass and are not influenced by charge. Electrostatic forces, on the other hand, depend on the charge of the objects involved and not on mass. Therefore, this option misrepresents the nature of both forces. ### Summary of Key Points: - Gravitational forces are always attractive, while electrostatic forces can be attractive or repulsive. - Gravitational forces act between masses, while electrostatic forces act between charged particles. - Electrostatic forces are generally much stronger than gravitational forces at small distances. - Understanding the nature of these forces is crucial for solving problems in physics related to motion, fields, and interactions. This understanding of the differences between electrostatic and gravitational forces is fundamental in physics and helps in analyzing various physical phenomena.