Motion in a plane is referred as motion in 2 dimension, for example, circular motion, projectile motion, etc. For analysing a 2 Dimensional motion the reference will be made of an origin with two coordinate axes i.e X and Y. Scalar quantities are those physical qualities that can be specified completely by their magnitude alone. The examples of scalar quantities are mass, density, temperature, length, work, speed, etc. However, vector quantities are specified by both magnitude and direction. The examples of vector quantities are displacement, acceleration, momentum, velocity, torque, force, etc. The direction of any vector quantity is specified by a unit vector. Vectors lying in the same or parallel to the same plane are called coplanar vectors.
Projectile motion is one of the most common examples of motion in a plane. When an object moves in a circular path at a constant speed, then the object is said to be in a uniform circular motion. The time period of a uniform circular motion is the time taken by an object to complete one complete revolution in its circular path. To maintain an object in its uniform circular motion a radially inward acceleration must be maintained continuously, it is called as centripetal acceleration.
The students can clear all their concepts related to this unit by referring to the motion in a plane class 11 notes from the links given below: