9.1.1 Einstein's Postulates Flashcards
Einstein’s Postulates
• Velocities are relative, not absolute. They are always measured with respect to a reference frame.
• The Galilean transformations relate the coordinates of an event in one frame to its coordinates in another frame. While intuitive, these equations are inaccurate at relativistic speeds.
• Light does not require a medium for its propagation. There is no special frame in which the “actual” speed of light is measured.
• Einstein’s postulates for his special theory of relativity:
- The laws of physics are the same in every inertial reference frame.
- The speed of light (in vacuum) is the same for all observers in inertial reference frames regardless of their motion or the motion of the light source.
The speed of light, c, has been experimentally calculated with great accuracy. Which of the following values of c is incorrect?
c = 186,000 mi/h
Two rockets, Rocket A and Rocket B, are moving with the same velocity v, but in opposite directions. Rocket A is projecting a beam of light ahead of it, in a direction parallel to the direction of the rockets’ travel. Before Einstein, Galilean relativity and Newtonian physics would have predicted that as observed by Rocket B, the speed of that beam of light would be ___________. Einstein theorized that the perceived speed of that beam of light would be _________.
c + 2v; c
In Newton’s theory, just as in Einstein’s theory of special relativity, inertial frames play an important role. By definition, an isolated particle in an inertial frame stays at rest or continues to move with uniform speed in a straight line. Which Newton’s law states this property of inertial frames?
Newton’s first law
Based on Einstein’s theory of special relativity, which of the following statements about inertial reference frames is incorrect?
Observers in an inertial frame can do experiments that enable them to determine if the inertial frame is at rest or moving.
True or false?
If S1 is an inertial frame and S2 is moving at uniform velocity relative to S1, then S2 is also an inertial frame.
true
Inertial frames S1 and S2 are moving relative to each other with uniform speed v. The coordinates of an event in S1 re (x1, t1) and the coordinates of the same event in S2 are (x2, t2). According to Galilean relativity, which of the following is the relationship between the coordinates of the event in the respective frames shown in the figure?
x2 = x1 + vt1 t2 = t1 = t
Consider two inertial frames S1 and S2 in relative motion. Which of the following does not apply to the state of motion of inertial frame S1? The answer choices are based on observations made by either an observer at rest in S1 or an observer watching S1 from another inertial frame S2.
The observer in S2 notes that S1 is changing speed uniformly.
Which of the following is not valid for Newton’s laws?
Time is relative; that is, the time of an event depends on the reference frame in which measurement is made.
