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.
Weeks or months of slightly slower growth alternate with mini growth spurts in most children. Kids actually tend to grow a bit faster in the spring than during other times of the year! A major growth spurt occurs at the time of puberty, usually between age 8 to 13 years in girls and 10 to 15 years in boys. Puberty lasts about 2 to 5 years.