Position.

Position of an object or point is expressed in terms of co-ordinates.Position of any point is completely expressed by two factors: Its distance from the observer and its direction with respect to observer.

That is why position is characterized by a vector known as position vector.

Let point P is in a xy plane and its coordinates are (x, y). Then position vector  of point will be     and if the point P is in a space and its coordinates are (x, y, z) then position vector can be expressed as

Frame of reference: It is a combination of system of coordinates connected to  an observer at the origin with a clock with him. Distance, velocity etc.. are measured with respect frame of reference.

OR

Frame of Reference : It is a system to which a set of coordinates are attached and with reference to which observer describes any event.

 

Frame of reference are of two types: (i) Inertial Frame of Reference  (ii) Non-Inertial Frame of Reference

Rest and Motion.

Rest: If a body does not change its position as time passes with respect to frame of reference, it is said to be at rest.

Motion: If a body changes its position with respect to time and frame of reference, it is said to be in motion.

Types of Motion.

(1) One dimensional Motion: If a body moves along a straight line , motion is said to be 1-D Motion.

When only one coordinate of the position of a body changes with time then it is said to be 1-D Motion.

Example : Motion of a freely falling body.

 

Two Dimensional Motion: Motion of body in a plane is called two dimensional motion, when two coordinates of the position of a body changes with time then it is said to be moving two dimensionally. Example : Motion of a projectile. 

 

Three dimensional Motion: Motion of body in a space is called three dimensional motion, when all three coordinates of the position of a body changes with time then it is said to be moving three dimensionally. Example motion of a bee.

 

Particle or Point Mass.

A matter  with zero dimension which can be described by its mass and position is defined as a particle.

Also If the size of a body is negligible in comparison to its range of motion then that body is known as a particle.

For example in a planetary motion around the sun the different planets can be presumed to be the particles.