83.1 Position and displacement of a particle 1. Several concepts Frame of reference -any object that is chosen for reference of a motion Coordinate system-the abstract of reference Particle-a single mass point without shape. + An object whose part are all move in exactly the same way can be treated as a particle; or a complex object can be treated as a particle if there are no internal motions or the internal motions can be neglected for the problem which you are discussing 83.1 Position and displacement of a particle 2. The position vector and displacement vector of a particle in rectilinear motion Hi=il Displacement--the change of the position vector A=r-1=(x s-Ci)i=4xi Note: The magnitude of the displacement is not necessarily equal to the total distance as traveled by the particle during the time interval At. when Ar=0. As may be not zero2 §3.1 Position and displacement of a particle 1. Several concepts Frame of reference —any object that is chosen for reference of a motion. Particle—a single mass point without shape. An object whose part are all move in exactly the same way can be treated as a particle; or a complex object can be treated as a particle if there are no internal motions or the internal motions can be neglected for the problem which you are discussing. Coordinate system—the abstract of reference 2. The position vector and displacement vector of a particle in rectilinear motion x O r x i i i ˆ = r x O r x i f f ˆ = r Note: r r r x x i xi f i f i ˆ ˆ ∆ = − = ( − ) = ∆ r r r Displacement—the change of the position vector §3.1 Position and displacement of a particle 1 The magnitude of the displacement is not necessarily equal to the total distance traveled by the particle during the time interval ∆t .when ∆r = 0 , ∆s may be not zero. r ∆s