# Chapter 9 : Special Theory of Relativity¶

## Example number 1 , Page number 284¶

In [12]:
#importing modules
import math
from __future__ import division

#Variable declaration
l=2*6371        #Diameter of earth
v=30            #velocity
c=3*10**5       #velocity of light

#Calculations
dell=(l*v**2)/(2*c**2)/10**-5

#Result
print"Change in length in diameter=",round(dell,2),"*10**-2 m"

Change in length in diameter= 6.37 *10**-2 m


## Example number 2 , Page number 284¶

In [27]:
#importing modules
import math
from __future__ import division

#Variable declaration
delt=10               #time duration at earth
delt1=1/365

#Calculations
v=math.sqrt(1-(delt1/delt)**2)

#Result
print"The minimum speed v= ",v,"c"

The minimum speed v=  0.99999996247 c


## Example number 3 , Page number 285¶

In [39]:
#importing modules
import math
from __future__ import division

#Variable declaration
L0=20           #The distance of the star
v=0.95          #velocity

#Calculations
t=L0/v
L=L0*math.sqrt(1-v**2)
L=round(L,1)
t1=(L*3*10**8)/(v*3*10**8)

#Result
print"(1) The time taken on earth (t) = ",round(t,2),"year"
print"(2) The time taken on spaceship  (t1) = ",round(t1,2),"year"

(1) The time taken on earth (t) =  21.05 year
(2) The time taken on spaceship  (t1) =  6.53 year


## Example number 4 , Page number 285¶

In [45]:
#importing modules
import math
from __future__ import division

#Variable declaration
L=5 #Lenth
v=0.6 #velocity
t=10 #time

#Calculations
L0=L/math.sqrt(1-v**2)
t1=t*math.sqrt(1-v**2)

#Result
print"(1) The height will be same and the length(L0)  = ",L0,"m"
print"(2) The time elapsed on his friend's watch(t1) = ",t1,"sec"

(1) The height will be same and the length(L0)  =  6.25 m
(2) The time elapsed on his friend's watch(t1) =  8.0 sec