Einstein's
First Postulate of Special Relativity
The first postulate is most easily understood by
comparing measurements you make in a stationary reference
frame to measurements you make for the identical
situation while you are in an airplane traveling at a
constant velocity of
300 miles per hour.
Question:
 If you were stationary, you would drop a ball and
it would drop straight down. What about on the
airplane traveling 300 miles per hour. What would
happen to the dropped ball?
Question:
 If you were stationary and you pushed a 0.15 kg
baseball forward with a force of 62.8 Newtons over a
distance of 2.0 meters:
 What acceleration
would the ball experience?
 What initial velocity
would the ball have with respect to you?
 What final velocity
would the ball have with respect to you?
Question:
 If you were in a plane traveling at 300 miles per
hour and pushed a 0.15 kg baseball forward with a
force of 62.8 Newtons over a distance of 2.0
meters:
 What acceleration
would the ball experience?
 What initial velocity
would the ball have with respect to you?
 What final velocity
would the ball have with respect to you?
If you were on a part of the trip where it was
completely smooth, and your velocity
stayted constant at 300 miles per hour, there is no lab
you could do that would verify your movement. Scientists
believe that every experiment they perform "at rest" on
the earth would be the same if performed on the smooth
airplane ride.
The laws of physics are the same in all reference
frames moving with constant
velocities!
