Puberty in females
During puberty, the female sexual organs grow, and menstruation begins. After this, pregnancy can occur.
The first sign may be a vaginal discharge, and the appearance of body hair in the pubic area, under the arms, and on the legs.
Skin becomes more oily, and the body produces more sweat, making deodorant necessary. This is because the oil and sweat glands are developing. Acne is also common.
Changes appear in the shape and size of the body:
The breasts start to grow, often starting with a small and sometimes painful lump just below the nipple
The hips widen, the waist becomes proportionally smaller, and extra fat will develop on the stomach and buttocks
The arms, legs, hands, and feet may grow faster than other parts of the body.
Some girls feel uncomfortable during this stage of development, but it is normal. The accumulation of extra fat is normal, and it does not necessarily mean that the girl is overweight.
Emotions may fluctuate, causing irritability, especially around the time of the monthly period. This is because hormone levels vary during the menstrual cycle.
If the emotional changes become too strong, a doctor may be able to provide medication or suggest lifestyle changes that can help, such as regular physical exercise to help reduce the effects of premenstrual tension (PMT) or premenstrual syndrome (PMS).
Puberty in males
As boys enter puberty, the scrotum becomes thinner and redder, and the testicles start to grow. Around the age of 13 years, the penis grows and lengthens.
The voice box, or larynx, gets bigger, the muscles or vocal cords grow, and the voice will "break" or "crack," and eventually become deeper.
There may be "wet dreams," when the boy ejaculates while sleeping, and wakes up in the morning to find damp sheets and pajamas. Involuntary erections can also occur at this time.
These things happen automatically, usually without the penis being touched and without the boy having sexual thoughts or dreams. He cannot prevent it from happening: it is just part of growing up.
Breast enlargement is not unusual. Hormonal changes may cause a bump under one or both nipples that can feel tender, or even painful. Eventually, the swelling and pain will disappear.
The skin becomes more oily, and there will be more sweat, because the oil and sweat glands are growing. Deodorant may be needed. Acne is common.
Body size will change, and there will be growth spurts, peaking about 2 years after puberty begins.
The arms, legs, hands, and feet may grow faster than other parts of the body, making the boy may feel clumsy. Total body fat content will start to drop as muscle develops.
Body hair starts to grow around the pubic area, under the arms, and on the legs and arms, and facial hair appears around the upper lip and chin.
Facial hair can be shaved off. This can cause a rash, especially if the boy has sensitive skin, but shaving foam or gel may help to prevent rashes. Electric razors reduce the risk of cuts.
Emotions change, and there may be mood swings. One moment, the young man may feel like laughing, and then he may suddenly feel like crying. There may be intense feelings of anger.
This is partly because of the increased levels of hormones in the body, but also because it can be hard to come to terms with all the physical changes that are taking place.
Both boys and girls may need support at this time, for example, an older family member or a friend to talk to about the changes and how to manage them.
P.S (This information belongs to the rightful owner. Do not declare plagiarizing someone's property.)
answer:answer is second postulate (invariance of c)
explanation:postulate (principle of relativity) laws of physics take the same form in all inertial frames of reference. postulate (invariance of c) measured in any inertial frame of reference, light is always propagated in empty space with a definite velocity c that is independent of the state of motion of the emitting body. or the speed of light in free space has the same value c in all inertial frames of reference.
the two-postulate basis for special relativity is the one historically used by einstein, and it remains the starting point today.