Question

when the price of input increases does demand shift?

Answer 1

Short answer: No — an increase in an input price does not shift the demand curve for the final good; it shifts the supply curve.

Explanation:
- A rise in an input price (e.g., steel for car makers) raises firms' costs. That causes the supply curve for the final good to shift left (decrease in supply).
- The leftward supply shift raises the equilibrium price of the final good and reduces the equilibrium quantity. The fall in quantity demanded is a movement along the demand curve (caused by the higher market price), not a shift of the demand curve.
- The demand curve only shifts when a non-price determinant of demand changes (income, tastes, price of substitutes/complements, expectations, number of buyers).

Two clarifications:
- If you mean the demand for the input itself: a higher input price leads to a lower quantity demanded of that input (movement along the input’s demand curve), unless other factors change.
- If the input-price change affects consumers’ incomes or preferences (rare direct channel), it could indirectly shift demand for the final good — but the usual, direct effect is on supply.