Consider two
objects. The first object moves with velocity
with respect to an observer. In Newtonian physics the
observer would say that the velocity of the first object
is the sum of the two velocities. uHowever, this would allow the observed velocity to exceed the speed of light. In fact, when relativistic effects are accounted for the expression becomes One can check
that this velocity never exceeds the speed of light by
working out the result when either equals the speed of light.
In that case, v will be the
speed of light. This is consistent with the postulate
that the speed of light is the same in all reference
frames.v'Velocity
addition problems, can be stated in many ways, often with
subtraction of velocities being used rather than
addition. The best strategy for approaching some problems
is to always write the Newtonian expression first. Then
use the relativistic expression above, assigning to whatever velocities
are on the right hand side of the expression. If the
Newtonian expression has a negative velocity, one must
remember to make the velcity in the numerator negative as
well.v |