Explanation:

The value of the coefficient of friction is taken at the moment when the block is at the verge of moving. This means that the block is on the verge of overcoming static friction and starting to move.

Coefficient of Friction:
The coefficient of friction is a dimensionless number that represents the ratio of the force of friction between two objects to the normal force between them. It quantifies the resistance to motion between two surfaces in contact.

Static Friction:
Static friction is the force that resists the initiation of motion when an object is at rest. It is a reactionary force that prevents one object from sliding or slipping on another object.

Dynamic (Kinetic) Friction:
Dynamic friction, also known as kinetic friction, is the force that opposes the motion of two objects that are sliding or slipping against each other.

At the Verge of Moving:
When a block is at the verge of moving, it means that the applied force is just enough to overcome the static friction between the block and the surface it is resting on. The static friction force is equal and opposite to the applied force, preventing the block from moving. At the verge of moving, the static friction force is at its maximum value.

Calculating the Coefficient of Friction:
To calculate the coefficient of friction, we can use the equation:

Coefficient of friction = Force of friction / Normal force

At the verge of moving, the force of friction is equal to the maximum static friction force, and the normal force is the weight of the object. Therefore, the coefficient of friction can be calculated using the equation:

Coefficient of friction = Maximum static friction force / Weight of the object

Conclusion:
In conclusion, the value of the coefficient of friction is taken at the moment when the block is at the verge of moving. This is because this is the point where the static friction force is at its maximum and equal to the applied force.