A change in quantity demanded (or a movement along the demand curve) is caused by a change in its own price while a change in demand (or a shift of the demand curve) is caused by a change in nonprice determinants that include changes in consumers' income, taste or preference, price of other goods, expected future price, etcetera.

What is the relationship between Coke andPepsi? Do they have the same demand curve or are they different?