Chapter 1 Concepts of Motion
1.1 Motion Diagrams
Motion is defined as the change of an object’s position with time.
The path along which an object moves, which might be a straight line or might be curved, is called a
Motion diagram shows an object’s position at several equally spaced instants of time. (1) If an object
occupies only a single position in a motion diagram, then that object is at rest. (2) Images that are
equally spaced indicate an object moving with constant speed. (3) An increasing distance between the
images shows that the object is speeding up. (4) A decreasing distance between the images shows that
the object is slowing down.
1.2 The Particle Model
Transitional motion is the motion of an object along a trajectory
An object that can be represented as a mass at a single point in space is called a particle. A particle has
no size, no shape and no distinction between top and bottom.
The particle model of motion is a simplification in which we treat a moving object as if all of its mass
were concentrated at a single point.
1.3 Position and Time
An arrow drawn from the origin to an object’s position is called the position vector of the object and it is
given the symbol r.
A scalar quantity can be positive, negative or zero.
A vector quantity can have a magnitude as well as a direction. The magnitude of the vector can be
positive or zero but it cannot be negative.
Displacement is the change in position. The displacement is a quantity that is independent of the
The displacement (change in r) of an object as it moves from an initial position to a final position