Reference Frame First Law Newtons first law says

Reference Frame

First Law ] Newton’s first law says that with no net force there is no acceleration. • Objects at rest • Objects at constant velocity ] If there is no observed acceleration on an object with no net force, the observer is in an inertial reference frame. • Newton’s laws of mechanics apply equally • No absolute motion

Inertial Frame ] An observer on the table sees two ball fall. • First straight down • Second in a parabola ] An observer with speed vx 0 sees the reverse. • Second straight down • First in a backwards parabola ] Both frames are inertial. • Motion consistent with Newton

Accelerated Frame ] A rotating observer throws a ball across a merry-go-round. • Ball veers to the side • No external force ] This is a non-inertial frame. • Observed motion inconsistent with Newton’s laws • Fictitious forces

Galilean Relativity ] An event is a point in space and time. • Described by coordinates: (x, y, z, t) ] A different frame of reference uses different coordinates. ] The Galilean transformation converts between two inertial frames. • Coincide at t = 0 y S y’ S’ v Event P x x’

Relative Velocity ] The Galilean transformation provides a conversion for relative velocity. y S y’ P • Moving event P • Observed velocity u, u’ x v S’ u’ u x’

Moving Light ] Light as a wave should have a medium for transmission. ether • Like a plane in the wind • Speed in ether c light observed ] The ether velocity and the light velocity must add to get the result from the earth.

Universal Constant ] Maxwell’s equations assume a constant value for c. • Independent of motion • Independent of observer ] Mechanical waves should follow Galilean relativity. • Speed depends on observer’s relative motion ] This was the paradox of the “ether”. • Newton and Maxwell contradict next