Describing Motion: Kinematics in One Dimension Chapter 2 Describing Motion: Kinematics in One Dimension

Today: Units of Chapter 2 Reference Frames Displacement and Distance Average Velocity Instantaneous Velocity (optional for us)

2-1 Reference Frames Any measurement of position, distance, or speed must be made with respect to a reference frame. It can be anything: a street corner, the Earth, a point… example: a person is walking down the aisle (5m/s) of a moving train (20 m/s). ex: moving frames (http://www.phys.unsw.edu.au/einsteinlight/jw/module1_Inertial.htm#IR) Earth-Sun (http://www.mesoscale.iastate.edu/agron206/animations/01_EarthSun.html) we will use systems of coordinates most of the times!

2-1 Displacement and Distance distance displacement. Displacement (blue line) = how far the object is from its starting point, regardless of how it got there. VECTOR! Distance traveled (dashed line) = measured along the actual path. SCALAR (= just a number)!

Vectors = mathematical models which have: Magnitude (= value) – unique Direction – unique for us, in one dimension, the direction could be the sign, + is to the right, - is to the left Origin – not unique ( it could be changed without changing the vector)

2-1 Displacement (VECTOR) The displacement is written: Right: Displacement is positive. Left: Displacement is negative.

2-2 Average Velocity Speed: how far an object travels in a given time interval (m/s) Velocity includes directional information (m/s): In our first example, if the elapsed time is 10 seconds, calculate speed and velocity:

2-3 Instantaneous Velocity If time permits, discuss this concept on the board. If the moving object does not turn around, displacement will have the same value as the distance! and are virtually the same formula…

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