Kinematics

Descriptions of Motion aka “Kinematics” time ( t ) position (d)  displacement (  d) velocity (v) acceleration (a)

Distance vs. Displacement Distance is a scalar quantity. Displacement is a vector quantity.

Vector vs. Scalar Quantities Vector Quantity Fully described by both magnitude (number plus units) AND direction Examples: -position (d) -displacement (  d) -velocity (v) (notice the arrows) Scalar Quantity Fully described by magnitude alone Examples: - time ( t ) - distance ( d ) - speed (  ) (notice the italics )

Speed and Velocity  Speed is the magnitude of velocity - it only reflects how fast an object is traveling  Velocity is a vector - it is speed in a particular direction  Along a straight line  direction is indicated with a +/- sign

Calculating Velocity Average velocity is the displacement divided by the total time interval: v av = ∆d∆t∆d∆t = d – d 0 t – t 0 ∆ (delta)  means “change in” Instantaneous velocity is the velocity of the object at any given instant in time. Constant (uniform) velocity means non-changing velocity.

Equation Notations in Physics: Quantities are expressed in variable form with a subscript used to describe different points in time v = d f - d i or d 1 – d 0 t f - t i t 1 – t 0 To simplify equations we will always assume, unless very specifically told otherwise, that t i = 0 Initial positions, velocities, etc. will be represented by the subscript 0 ( v 0, d 0, etc.) and final values will have no subscript at all ( v 1, d 1, t 1, etc.)