The correct answer is A fan blade rotating at constant speed. Explanation & Key Takeaways: • Uniform Circular Motion (UCM): It refers to the motion of an object in a circular path with a constant speed. Although the speed remains constant, the direction of velocity changes continuously, resulting in acceleration known as centripetal acceleration. • A fan blade rotating at constant speed: The fan blade undergoes uniform circular motion because each point on the blade moves along a circular path at a constant speed, with centripetal force acting towards the center of the fan. This is the correct example of UCM. • A ball thrown vertically upwards: This motion is linear (not circular) and is influenced by gravitational force, causing the ball to decelerate while moving up and accelerate while coming down. Hence, this is not an example of UCM. • A car accelerating on its way: The car’s motion is typically along a straight or curved path with changing speed and direction. Both the velocity and acceleration change, making it non-uniform motion. This is not an example of UCM. • A train moving on its track: Unless specified that the train is moving in a circular path at constant speed, this is generally linear motion. Hence, this is not an example of UCM. Related Concepts: • Characteristics of Uniform Circular Motion (UCM): • Constant Speed: The magnitude of velocity remains unchanged throughout the motion. • Changing Velocity Direction: Since the object is moving in a circle, the direction of velocity changes continuously. • Centripetal Acceleration: The acceleration is directed towards the center of the circle and is responsible for changing the direction of velocity. • Centripetal Force: The force that keeps the object in circular motion acts towards the center of the circle. • Examples: A satellite orbiting Earth, a stone tied to a string and whirled in a circle, and planets revolving around the Sun. • Non-Uniform Circular Motion: • If the speed of the object moving in a circular path changes, it is called non-uniform circular motion. • In this case, both tangential acceleration (due to changing speed) and centripetal acceleration (due to changing direction) are present. • Difference Between Uniform and Non-Uniform Circular Motion: • Uniform Circular Motion: Constant speed with changing velocity direction; only centripetal acceleration is present. • Non-Uniform Circular Motion: Changing speed and direction of velocity; both centripetal and tangential accelerations are present. • Applications of UCM: • Artificial Satellites: Satellites revolve around Earth in uniform circular motion under the influence of gravitational force. • Vehicle Turns: Vehicles negotiating circular turns demonstrate the concept of centripetal force. • Amusement Rides: Many rides in amusement parks use uniform circular motion principles to ensure thrilling yet safe experiences.