Where is the largest number of people in the world today? What will the population of North and Central America be in fifty years? The answers to these and many other questions are based on models. These models change over time and the amount they change depends on their current values. Models apply to many situations, from the motion of a child's swing, to the progress of a chemical reaction, to the population of the world.

Look at a map of the world. On which area of the world do you think the majority of people lived? Do you think that the majority of people will be in the same in each area in 2100? Discuss your thoughts with your partners.