The correct option is **A. Electrostatic forces can be attractive or repulsive, while gravitational forces are always attractive.** ### Detailed Explanation 1. **Understanding Electrostatic Forces:** - Electrostatic forces arise from the interaction between charged particles. These forces can either be attractive or repulsive: - **Attractive Forces:** Occur between opposite charges (positive and negative). For example, a positively charged object will attract a negatively charged object. - **Repulsive Forces:** Occur between like charges (positive-positive or negative-negative). For instance, two positively charged objects will repel each other. 2. **Understanding Gravitational Forces:** - Gravitational forces, on the other hand, are always attractive. They arise from the mass of objects and the gravitational interaction between them. For example, the Earth attracts all objects towards its center due to its mass. No matter the masses involved, gravitational forces will always pull objects together. 3. **Why Option A is Correct:** - The key difference highlighted in option A is fundamental to the nature of these two forces. The ability of electrostatic forces to be both attractive and repulsive allows for a wide range of interactions in physics, such as the formation of atoms and molecules. In contrast, the always-attractive nature of gravitational forces leads to phenomena like the orbits of planets and the structure of galaxies. ### Why the Other Options are Incorrect **B. Gravitational forces are significantly stronger than electrostatic forces at all distances.** - This statement is incorrect. While gravitational forces are very weak compared to electrostatic forces at the scale of atomic and subatomic particles, they dominate at larger scales (like planets and stars) due to the cumulative effect of mass. At small distances, electrostatic forces are much stronger than gravitational forces. For example, the electrostatic force between two electrons is about \(10^{42}\) times stronger than the gravitational force between them. **C. Electrostatic forces do not follow the inverse-square law, whereas gravitational forces do.** - This statement is also incorrect. Both electrostatic and gravitational forces follow the inverse-square law. The mathematical expressions for both forces are: - **Electrostatic Force (Coulomb's Law):** \( F = k \frac{|q_1 q_2|}{r^2} \) - **Gravitational Force (Newton's Law of Gravitation):** \( F = G \frac{m_1 m_2}{r^2} \) - Here, \(k\) is Coulomb's constant, \(G\) is the gravitational constant, \(q_1\) and \(q_2\) are the charges, \(m_1\) and \(m_2\) are the masses, and \(r\) is the distance between the centers of the two objects. Both forces decrease with the square of the distance between the objects. **D. Gravitational forces act only on charged objects, while electrostatic forces act on all masses.** - This statement is incorrect. Gravitational forces act on all objects with mass, regardless of whether they are charged or not. Every mass attracts every other mass, which is a fundamental principle of gravity. Electrostatic forces, however, only act on charged objects. Therefore, this statement misrepresents the nature of gravitational forces. ### Summary of Key Points - **Electrostatic forces can be attractive or repulsive**, depending on the nature of the charges involved. - **Gravitational forces are always attractive**, acting between any two masses. - Both forces follow the **inverse-square law**, but their strengths vary significantly depending on the scale and nature of the objects involved. - Gravitational forces act on **all masses**, while electrostatic forces act only on **charged objects**. This understanding of the differences between electrostatic and gravitational forces is crucial for grasping many concepts in physics, from atomic interactions to celestial mechanics.