Motion In A Straight Line
Rest:
An object is said to be at rest if it does not change its position with respect to its surroundings. In other words, the object's position remains constant over time.
Rest is a relative concept; an object may be at rest with respect to one observer but in motion with respect to another observer.
Motion:
Motion is the change in position of an object with respect to its surroundings in a given time interval.
Like rest, motion is also relative. An object can be in motion with respect to one observer and at rest with respect to another observer.
Motion is described in terms of various parameters such as speed , velocity and acceleration.
Reference Frame:
The description of rest or motion depends on the choice of a reference frame. A reference frame is a set of coordinate axes relative to which the position and motion of an object can be described.
For example, if you're on a moving train, your reference frame is different from someone standing on the platform. An object may appear at rest in the train's reference frame but in motion from the platform's reference frame.can be at rest as well as in motion at the same time.
Ex : A person sitting in the compartment of a moving train is in the state of rest, withrespect to the surroundings of compartment. Yet he is in the state of motion, if he compareshimself with surroundings outside the compartment.
Scalars:The physical quantities which have only magnitude but not direction are called scalars.
Ex: Mass, length, distance, time, area, volume, density, work etc.
Vectors: The physical quantities which have both magnitude and direction are called vectors.
Ex: Displacement, velocity, acceleration, force etc.