Einsteins Laws First Law Newtons first law says

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 1638. – Galilean relativity – Basis for Newton • The Galilean transformation describes velocities as sums. y S y’ S’ x v Event P x’ x x’

Moving Light medium observed source 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.

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

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