Know the following two ideas, or postulates of Einstein...
- The speed of light is constant in all reference frames
-All the laws of nature are the same in all uniformly
moving frames of reference.
Imagine yourself in a spaceship, and you are travelling
at a speed close to the speed of light. In the spaceship cabin with you
is a laser beam that goes up and down to measure time. To the person
inside the spaceship, or moving person the laser beam goes up and down,
while to a stationary person, the observer sees the laser beam rise at
a certain angle from the horizontal, and therefore it travels a different
distance with the same velocity, known by the constant c, so the time must
be longer to the person outside, the observer.
---Note: A reference frame is where you view it
from.
Also, as the speed of the object approaches the speed
of light, two other effects are noticeable to any outside observer. To
the object moving at fast speeds, its mass and length are unchanged. But
to an outside observer, the mass of the object is increasing, and it's
length is observed to shrink in the direction of motion. In
other words, say a meter stick is moving at a speed close to the speed
of light. It's mass is increased, and it is less than one meter long.
In the equation, Property 1 and Property 2 are the masses,
lengths, or times for an object and an observer. Property 1 is the
property that is bigger and Propety 2 is the one that is smaller.
you must decide which is right for each situation. Remeber, mass
and time increse to the observer, while length decreases.
Sample Problems:
1.) Using the above equation, an object of rest mass 5.97kg, and a rest length of 6.28m, travels for 30 sec (in it's frame of reference) at a velocity of 89% the speed of light, find:
a.)it's moving mass
b.)it's moving length
c.)the stationary time