The rotational effect of a force acting on a body about a given axis of rotation is described in physics in terms of which quantity?

Introduction / Context:
When a force acts on a rigid body, it can cause translation, rotation or both, depending on the line of action and point of application. To describe the tendency of a force to produce rotation about a specific axis, physics uses a special quantity. This question asks for the correct term used to express the rotational effect of a force about an axis of rotation.

Given Data / Assumptions:

• A force is acting on a body that can rotate about a fixed axis.
• The line of action of the force is at some perpendicular distance from this axis.
• We want the quantity that measures how effectively this force tends to rotate the body.
• We assume basic rigid body mechanics and ignore friction for the definition.

Concept / Approach:
The rotational effect of a force about an axis is measured by the moment of force, also called torque. It is defined as the product of the magnitude of the force and the perpendicular distance from the axis of rotation to the line of action of the force. A larger force or a larger perpendicular distance produces a larger moment and stronger tendency to rotate. Other terms like centripetal or centrifugal force describe different concepts related to circular motion, not the rotation causing ability of a single force about a pivot.

Step-by-Step Solution:
Step 1: Consider a lever or a door hinged at one side. When you push at the handle, the door rotates about its hinges. Step 2: The force applied at the handle has a certain magnitude and acts at a distance from the hinge line. Step 3: The rotational tendency depends on both how large the force is and how far from the hinge it is applied. Step 4: In physics, this product of force and perpendicular distance is called the moment of force or torque. Step 5: Therefore, the correct term for the rotational effect of a force about an axis is moment of force.

Verification / Alternative check:
The formula for moment of force is often written as tau equals F times d, where tau is torque or moment, F is the applied force and d is the perpendicular distance from the axis. This concept explains many real devices such as spanners, levers and seesaws. The greater the torque, the easier it is to rotate the object. Physics texts consistently use the term moment of force or torque for this effect, while reserving centripetal and centrifugal forces for circular motion dynamics, confirming the correct option.

Why Other Options Are Wrong:
Centre of gravity is the point where the weight of the body effectively acts; it is not a measure of rotational effect of an external force.
Centripetal force is the force that keeps a body moving in a circular path, directed toward the centre, not a measure of torque.
Centrifugal force is a perceived outward force in a rotating frame and does not quantify the turning effect of a single applied force about a pivot.
Linear momentum deals with straight line motion (mass times velocity) and is not a measure of rotation about a point.

Common Pitfalls:
Students sometimes mix up centripetal force and torque because both are associated with circular motion. However, centripetal force is about maintaining circular motion, while moment of force is about starting or influencing rotation about an axis. Another mistake is to think centre of gravity is automatically related to any rotational question, when in fact it only describes where the weight acts. Always remember that the term torque or moment of force is specifically about the rotational effect of a force around a pivot or axis.

Final Answer:
The rotational effect of a force about an axis is described in terms of the moment of force (torque).