Movement along the supply curve is caused due to change in the price of the commodity keeping other factors constant. If the price of that commodity rises, its quantity supply will also rise causing upward movement along the supply curve (i.e. extension of supply) as shown in fig. A. On the other hand, if the price of the commodity falls showing downward movement along the supply curve (i.e. contraction of supply) indicated by downward arrow in fig.B.
