Vector

Parallel vectors are vectors that have the same direction or exactly opposite direction.

1. If two vectors are parallel then they are scalar multiples of each other. A=kB where k is a real number.

2. If two vectors are parallel their cross product is zero. $A\times B=0$ 

3. If two vectors are parallel their dot product is equal to the product of their magnitudes. $A\cdot B=|A||B|$ 

4. If two vectors are parallel then triangle law is applicable in case of their addition.

5. If two parallel verctors magnitude is equal then the vectors are equal as well. 

The vector with zero magnitude is called zero vector or null vector. It has no direction defined.