when is an object said to be in uniform circular motion
Circular motion In physics, circular motion is a movement of an object along the circumference of a circle or rotation along a circular path. It can be uniform, with constant angular rate of rotation and constant speed, or non-uniform with a changing rate of rotation. The rotation around a fixed axis of a three-dimensional body involves circular motion of its parts. The equations of motion describe the movement of the center of mass of a body.
Rest (physics) In physics, rest is the state of an object being stationary relative to a particular frame of reference or another object; when the position of a body with respect to its surroundings does not change with time it is said to be "at rest". According to the theory of relativity, it is said that an object is "at rest relative to" another. For example, a train decelerates approaching a station and eventually comes to rest alongside the platform. The train can be said to be "at rest with respect to the station", or, as the correct frame of reference is usually implicit and/or provided by context, simply "at rest". In reality, there is nothing at absolute rest. For example, Earth's gravitation constantly pulls objects toward its surface, while Earth is one of the objects the Sun constantly pulls towards itself, causing it to orbit the Sun; the Sun, in turn, orbits the center of the Milky Way; and so on.