Action and reaction

Options

A. act on two different objects
B. have equal magnitude
C. have opposite directions
D. have resultant zero.

Answer

To solve the question regarding action and reaction forces, we will analyze the situation step by step based on Newton's Third Law of Motion.

### Step-by-Step Solution:

1. **Understanding Action and Reaction Forces**:
- According to Newton's Third Law, for every action, there is an equal and opposite reaction. This means that if one object exerts a force on another object, the second object exerts a force of equal magnitude but in the opposite direction on the first object.

2. **Identifying the Forces**:
- Let's consider an object (e.g., a book) resting on a surface (e.g., a table). The weight of the object (mg, where m is mass and g is acceleration due to gravity) acts downward on the object due to gravity. This downward force can be termed as the "action force".

3. **Reaction Force**:
- The surface (table) exerts a normal force (N) upward on the object. This force is the reaction force that acts in response to the action force (weight of the object). According to Newton's Third Law, this normal force is equal in magnitude to the weight of the object (N = mg) and acts in the opposite direction.

4. **Analyzing the Options**:
- **Option 1: Act on two different objects**: This is correct. The action force (weight of the object) acts on the object, while the reaction force (normal force) acts on the surface.
- **Option 2: Have equal magnitude**: This is also correct. The magnitudes of the action and reaction forces are equal (N = mg).
- **Option 3: Have opposite directions**: This is correct as well. The action force acts downward, while the reaction force acts upward.
- **Option 4: Have resultant zero**: This is also correct. Since the action and reaction forces are equal and opposite, their resultant force is zero when considering the object in equilibrium.

5. **Conclusion**:
- All four options provided in the question are correct based on the principles of action and reaction forces as described by Newton's Third Law.

### Summary of the Correct Options:
- All four options (1, 2, 3, and 4) are correct.