Just as on the demand side, the position of the supply can shift, say from a change in the price of a productive input or a technical improvement. The Law of Supply states that, in general, a rise in price leads to an expansion in supply and a fall in price leads to a contraction in supply.
Puberty takes place over a number of years, and the age at which it starts and ends varies widely. It generally begins somewhere between the ages of 7 and 13 for girls, and somewhere between the ages of 9 and 15 for guys, although it can be earlier or later for some people.
Most girls will have their growth spurt period between ages 10 and 14, during the early stages of puberty. During this growth spurt that lasts for a year or two, growth is rapid. They can grow as much as 3Â½ inches in height per year during this duration.