In the United States, the average age for a girl to get her first period is 12. This does not mean that all girls start at the same age. A girl can start her period anytime between the ages of 8 and 15. Most of the time, the first period starts about 2 years after breasts first start to develop. If a girl has not had her first period by age 15, or if it has been more than 2 to 3 years since breast growth started, she should see a doctor.
Cancel Save! You can build a balance beam out long pieces of wood covered with thick cloth, or sand it smooth so you don't get a splinter. A piece of wood laid on the ground is not a balance beam. Balance beams are 10 cm wide, 500 cm long, and usually 124 cm off the ground. Post Your Project.
Mass is the amount of matter an object has. We often use a triple-balance beam to measure mass. A triple-beam balance gets its name because it has three beams that allow you to move known masses along the beam. Here is a picture of a triple beam balance. You probably have used one in school. There are also many other types of balances. Scientists need balances that can measure very small amounts of mass. If you are interested at looking at the many other types of balances click here.