Variations in Prices

We already know that economists divide all the variables that could affect the demand into two groups, price and everything else. In geometric terms, this division is reflected on the fact that the variations of price move you all along the demand curve, while the other variables are combined to determine exact where they sit on the curve and the shape they have.

For example, if people were not into buying lettuce, they would not buy five of them for a price of $2. And actually, they would not buy it at all, no matter what the price was.

Movement of The Demand Curve
Given that the different factors of price determine where they sit on the demand curve and what shape they are in, if any of those factors changes, the demand curve moves.

For example, lets suppose that a public study is made about a topic concerning health, and this health study says that carrots make people more attractive to the opposite sex. a study and conclusion like this would definitely increase the demand for carrots.

When a curve of demand moves, economists say that there has been a demand shift.

In this way of describing the movements it is implicit to know the fact that the demanded amounts increase or decrease while the prices remain constant. It is important to highlight on that point: you should be able to distinguish between the changes that occur in the demanded amounts by variation in the prices, and the changes that occur in the demanded amounts because something different from the prices changes.

Keep in mind that any different thing from the price that affects the demanded amount moves the demand curve.