Considering the demand for hotdogs, the number/amount of consumers/income, and the substitution of pretzels, what would cause a movement along the demand curve and what would cause a shift of the demand curve for hotdogs?
For most products, the quantity demanded by customers of the product for a particular price is inversely proportional to the price of the product. As the price increases customers buy a smaller quantity and the quantity bought increases as the price decreases. This causes a movement along the same demand curve. There are many other factors that lead to a shift in the demand curve itself, examples of which are the total demand, the income of customers, a change in preference, a change in the availability of substitutes, etc.
The quantity demanded of hotdogs is influenced by a change in price of hotdogs, it follows the inverse ratio described earlier. Only this is responsible for a movement along the demand curve. The other two factors lead to the creation of a new demand curve.
in the second case, the demand curve shifts with the change in the price of salted pretzels that are a substitute for hot dogs and a change in consumers' income.