Question

What remains constant in a uniform circular motion?
(A). Speed
(B). Velocity
(C). Displacement
(D). Direction

Answer 1

- Hint: In a circular motion velocity, displacement, direction being vector quantities is changing continuously.

Complete step-by-step solution -

When a particle moves on a circular path about a given point, and that the radius of the circular path remains constant, the position vector of the particle with respect to the centre is changing continually. The circular motion is called uniform when the particle’s speed remains constant. The magnitude of velocity remains constant while the direction is changing, as therefore the velocity is changing, with the instantaneous velocity pointed tangentially to the circular path. Since, the direction is always changing, the displacement as a vector keeps changing.
Hence, the uniformity of uniform circular motion is due to its constant speed.

Therefore, the correct option is A.

Additional Information:
Since, most usual vector quantities don’t remain constant in a circular motion, we define new quantities in angular space. We define angular displacement as the ratio of arc length to the radius of the arc and angular velocity as rate of change of angular displacement. Angular velocity is also defined as the ratio of linear velocity (speed) to the radius of the curved path. During a uniform circular motion, the angular velocity remains constant.

Note: It is to be noted that although the speed remains constant in a uniform circular motion, owing to the change of velocity, there is an acceleration with constant magnitude and directed radially inward, to the centre of the curved path. This acceleration is called centripetal acceleration.