Animations taken from ppt on Isomerism from http://ibchem.com/ppt/index.htm
Animation 1: Geometrical Isomerism
Single covalent bonds can easily rotate. What appears to be a different structure in an alkane is not. Due to the way structures are written out, they are the same.
Animation 2:
RESTRICTED ROTATION OF C=C BONDS
C=C bonds have restricted rotation so the groups on either end of the bond are ‘frozen’ in one position; it isn’t easy to flip between the two.