General Physics (PHY 170) UHM（普通物理(PHY 170)嗯）.pdfVIP

General Physics (PHY 170) Chap. 3 Position, Displacement, Velocity, Acceleration Vectors 1 Motion in Two Dimensions Using + or – signs is not always sufficient to fully describe motion in more than one dimension Vectors can be used to more fully describe motion: displacement, velocity, and acceleration 2 Position, Displacement, Velocity, Acceleration Vectors The position vector r points from the origin to the location in question. The displacement vector r points from the original position to the final position. 3 The Displacement Vector ^ ^ r = Xx + Yy r = r -r 2 1 = = (X x +Y^ y) - (X^ x + Y^ y)^ 2 2 1 1 = xx +^ yy^ 4 The Average Velocity Vector Average velocity vector: is the ratio of the displacement to the time interval for the displacement V is in the same av direction as r. 5 The Instantaneous Velocity Vectors Instantaneous velocity vector: is the limit of the average velocity as t approaches zero. Its direction is along a line that is tangent to the path of the particle and in the direction of motion. 6 Velocity Vectors 7 Example: Velocity of a Sailboat A sailboat has coordinates (130 m, 205 m) at t =0.0 s. Two minutes 1 later its position is (110 m, 218 m). (a) Find v ; (b) Find |v