ENGINEERING PHYSICS
Topic :
• Lorentz Transformation
•Length Contraction
•Time Dilation
Name :
Branch : B.Tech
Computer Science (1)
Lorentz Transformation
The primed frame moves with velocity v in the x direction
with respect to the fixed reference frame. The reference
frames coincide at t=t'=0. The point x' is moving with the
primed frame.
S S’
P(x, y, z) in fixed frame P(x’, y’, z’) in moving frame
Lorentz Transformation implies: c2 t2 – (x2 + y2 + z2) = c2 t’2 – (x’2 + y’2 + z’2) (Lorentz
invariant)
x2 + y2 + z2 x’2 + y’2 + z’2
c2 = = is the same (speed of light )2 in the two frames
t2 t’2
t and t’ cannot be equal
Two “events” (x1, t1) and (x2, t2) at the same time t1 = t2 in S are do not happen at the same time in
S’, t1’ ≠ t2’.
Lorentz Transformation Equations
y = y’ z = z’
The reverse Lorentz
Transformation Equations
Direct Lorentz Transformation
Equations
Length Contraction
The length of any object in a moving frame will appear
foreshortened in the direction of motion, or contracted.
The amount of contraction can be calculated from the
Lorentz transformation. The length is maximum in the
frame in which the object is at rest.
Time Dilation
A clock in a moving frame will be seen to be running
slow, or "dilated" according to the Lorentz
transformation. The time will always be shortest as
measured in its rest frame. The time measured in the
frame in which the clock is at rest is called the "proper
time".
If the time interval T0 t '2 t '1 is measured in the moving reference
frame, then T t2 t1 can be calculated using the Lorentz transforma tion
vx'2 vx'1
t '2 2 t '1 2 The time measurements made
T t2 t1 c c in the moving frame are made at
the same location, so the
v2
1 2 expression reduces to:
c
T0
T T0
2
v
1
c2
For small velocities at which the relativity factor is very
close to 1, then the time dilation can be expanded in a
binomial expansion to get the approximate expression: