In uniform circular motion, the force that keeps a body moving along a circular path toward the centre is called what?

Introduction / Context:
When an object moves in a circle, its direction of motion is constantly changing, even if its speed remains constant. This change in direction requires a net force toward the centre of the circular path. This question tests your understanding of the correct name of that inward-directed force in basic physics terminology.

Given Data / Assumptions:

• An object is moving in a circular path with some speed.
• The motion is uniform circular motion, so the speed is constant but direction changes.
• A net force must be acting toward the centre of the circle.
• We are using standard Newtonian mechanics terminology.

Concept / Approach:
The force that acts toward the centre of a circle, causing an object to follow a circular path, is called centripetal force. The term "centripetal" literally means "seeking the centre." It is not a new kind of force by itself; it may be provided by tension, gravity, friction or another interaction, but its direction is always inward. The so-called "centrifugal force" is a pseudo-force that appears only in a rotating (non-inertial) frame of reference and is not the actual physical cause of circular motion in an inertial frame. Friction sometimes provides centripetal force (for example, between tyres and road), but friction is not always involved, so it cannot be named as the general force for all circular motion.

Step-by-Step Solution:
Step 1: Recall that for an object to move in a circle of radius r at speed v, there must be an inward acceleration given by a = v^2 / r. Step 2: According to Newton's second law, this inward acceleration must be produced by a net inward force, F = m * v^2 / r. Step 3: This inward-directed net force is called centripetal force. Step 4: Recognise that centrifugal force is a fictitious outward force that appears only when you analyse motion from a rotating frame, not the real cause of circular motion. Step 5: Note that friction may or may not be the source of centripetal force, so it cannot always be identified as the force keeping a body in circular motion.

Verification / Alternative check:
Examples from everyday life support this concept. In a stone tied to a string and whirled in a circle, the tension in the string provides centripetal force. In planetary orbits, gravity acts as the centripetal force, pulling the planet toward the star. In a car turning on a curved road, friction between tyres and road supplies the centripetal force. In all these cases, textbooks refer to the inward net force as centripetal, regardless of its physical origin. This confirms that "centripetal force" is the general term we use for the force that keeps an object in circular motion.

Why Other Options Are Wrong:
The centrifugal force: This is not a real force in an inertial frame; it is an apparent outward force experienced in a rotating frame and does not cause circular motion.

The frictional force: Friction can act as centripetal force in some cases, but not in all types of circular motion, and it is not the general name for the force required.
All of the above: This would incorrectly include centrifugal and frictional forces as general answers; the correct universal term is centripetal force only.

Common Pitfalls:
Students often confuse centripetal and centrifugal forces, sometimes thinking they are equal and opposite "real" forces. The safer way to think about it in basic physics is that centripetal force is the real inward force required for circular motion, while centrifugal force is an apparent effect in a rotating reference frame and should not be treated as the cause of the motion in standard problems.

Final Answer:
The force that keeps a body in circular motion is called the centripetal force.