The correct option is **D. Electrostatic forces can be either attractive or repulsive, while gravitational forces are always attractive.** ### Detailed Explanation 1. **Understanding Electrostatic Forces:** - Electrostatic 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 (\( 8.99 \times 10^9 \, \text{N m}^2/\text{C}^2 \)). - The nature of the force depends on the signs of the charges: - If both charges are of the same sign (both positive or both negative), the force is **repulsive**. - If the charges are of opposite signs (one positive and one negative), the force is **attractive**. 2. **Understanding Gravitational Forces:** - Gravitational forces, on the other hand, are always attractive. They arise from the mass of objects and are described by Newton's Law of Universal Gravitation: \[ F = G \frac{m_1 m_2}{r^2} \] where \( G \) is the gravitational constant (\( 6.674 \times 10^{-11} \, \text{N m}^2/\text{kg}^2 \)), and \( m_1 \) and \( m_2 \) are the masses of the two objects. - No matter the masses involved, the gravitational force will always pull the two masses toward each other. 3. **Comparing Strengths:** - At the atomic scale, electrostatic forces are significantly stronger than gravitational forces. For example, the electrostatic force between two protons is about \( 10^{36} \) times stronger than the gravitational force between them. This is crucial in understanding atomic structure and interactions. 4. **Distance Dependence:** - Both electrostatic and gravitational forces can act over long distances, but the strength of the forces diminishes with the square of the distance. However, electrostatic forces can be much stronger at short distances compared to gravitational forces. ### Why Other Options Are Incorrect - **Option A:** "Electrostatic forces are always attractive, while gravitational forces can be both attractive and repulsive." - This statement is incorrect because electrostatic forces can be both attractive and repulsive, depending on the nature of the charges involved. Gravitational forces, however, are always attractive. - **Option B:** "Gravitational forces are much stronger than electrostatic forces at the atomic scale." - This is false. As mentioned earlier, electrostatic forces are much stronger than gravitational forces at the atomic scale, which is why they dominate atomic interactions. - **Option C:** "Electrostatic forces can act over long distances, while gravitational forces only act over short distances." - This statement is misleading. Both forces can act over long distances, but the strength of the forces decreases with distance. Gravitational forces can act over astronomical distances, just like electrostatic forces. ### Summary for Revision - **Electrostatic forces can be attractive or repulsive** depending on the charges involved, while **gravitational forces are always attractive**. - **Electrostatic forces are much stronger than gravitational forces** at the atomic scale. - Both types of forces can act over long distances, but their strength diminishes with distance. - Understanding the nature of these forces is crucial for studying atomic interactions and gravitational effects in larger systems.