Einstein’s Laws

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 curve An moving with the second ball 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 Galileo described the conversion between inertial frames in –Galilean relativity –Basis for Newton The Galilean transformation describes velocities as sums. y x Sy’ x’ S’ Event Px x’ v

Moving Light Light as a wave should have a medium for transmission. –Velocity like a plane in the wind –Speed c without motion The earth’s velocity and the light velocity must add to get the result from the earth. observedsource light medium

Michelson-Morley An interferometer can split and recombine light. –Interference shifts for different paths In 1887 an experiment sowed the direction didn’t matter. The speed c must be a universal constant. mirror 2 mirror 1 semi- silvered mirror

Einstein’s Principles In 1905 Einstein described two basic principles. I. The laws of physics are the same in all inertial frames. II. The speed of light in a vacuum is the same for all inertial frames, from all sources.

Equivalence Principle The 1905 principles became known as special relativity. In 1915 Einstein added another principle to form general relativity. III.Gravitational mass is the same as inertial mass. descsite.nl