Final answer:
A change in demand represents a shift in the demand curve due to factors like income or consumer preferences, while a change in quantity demanded is a movement along the demand curve caused by a change in the good's price. Shifts in demand curves alter the equilibrium price and quantity in a market.
Step-by-step explanation:
A change in demand refers to a situation where, due to various factors such as income increases, consumer preferences, or price changes of substitute and complementary goods, the entire demand curve shifts. This means at the same price levels, the quantity demanded is either more or less than before. For example, with an increase in income, people can afford more of a good, leading to a shift in the demand curve to the right from Do to D1, indicating increased demand. Conversely, decreased demand would shift the demand curve to the left from Do to D2, showing at each given price, the quantity demanded is lower.
On the other hand, the change in quantity demanded is a movement along the same demand curve due to a change in the good's price. It does not involve shifting the demand curve but rather moving to a different point on the same curve. For instance, if the price of a car goes down, the quantity demanded at that lower price will increase, which is represented by a movement down along the demand curve. If the price goes up, the quantity demanded decreases, reflected by a movement up along the curve.
When a demand curve shifts, it will intersect a given supply curve at a new equilibrium point, affecting both the equilibrium price and quantity. This is a dynamic of market economics that plays out in scenarios ranging from grocery prices to real estate markets.