which of the following forces can never, under any circumstances, does work ?

Options

A. Static friction
B. Tension
C. Normal
D. None of these

Answer

To determine which of the following forces can never do work, we will analyze each option given: static friction, tension, normal reaction, and none of these.

### Step-by-Step Solution:

1. **Understanding Work Done by a Force**:
Work done (W) by a force is defined as the product of the force (F) and the displacement (d) in the direction of the force. Mathematically, it is given by:
\[ W = F \cdot d \cdot \cos(\theta) \]
where \(\theta\) is the angle between the force and the displacement.

2. **Analyzing Tension**:
Tension is a pulling force exerted by a string, rope, or cable. When a block is attached to a string and pulled, the tension does positive work as it acts in the direction of the displacement. Therefore, tension can do work.

3. **Analyzing Normal Reaction**:
The normal force acts perpendicular to the surface on which an object rests. If an object moves horizontally on a flat surface, the normal force does not contribute to the displacement in the direction of the force (since \(\theta = 90^\circ\) and \(\cos(90^\circ) = 0\)). However, if the object moves vertically (like in an elevator), the normal force can do work. Thus, normal reaction can sometimes do work depending on the situation.

4. **Analyzing Static Friction**:
Static friction acts to oppose the tendency of relative motion between two surfaces. It does not do work because there is no displacement when static friction is acting. If there is no relative motion, the displacement is zero, and thus:
\[ W = F \cdot 0 = 0 \]
Even when static friction acts on an object, it does not cause any displacement. Therefore, static friction can never do work.

5. **Conclusion**:
Based on the analysis, the force that can never do work under any circumstances is **static friction**.

### Final Answer:
The force that can never, under any circumstances, do work is **static friction**.