Python编程会产生错误

Question

我正在尝试为动能编译python程序。但它产生了错误

Traceback (most recent call last):
  File "/home/raj/Desktop/nn.py", line 5, in <module>
    E= m*v*v
TypeError: can't multiply sequence by non-int of type 'str'

代码

print "enter the value of mass "
m= raw_input()
print "enter the value of the velocity?"
v= raw_input()
E= m*v*v  
print  E

请解释我的错误。请更正