Weighing scales (usually just "scales" in UK and Australian English, "weighing machine" in South Asian English or "scale" in US English) is a measuring instrument for determining the weight or mass of an object. Weighing scales are used in many industrial and commercial applications, and products from feathers to loaded tractor-trailers are sold by weight. Specialized medical scales including infant medical scales, and bathroom scales are used to measure the body weight of human beings.
The name scales derives from the pair of scales or dishes in which objects to be weighed and the weights / masses against which to weigh them are placed. The Oxford English Dictionary defines scales as "Apparatus for weighing. The pan, or each of the pans, of a balance." Spring balances or spring scales measure force or weight by balancing the force due to gravity against the force on a spring, whereas a balance or pair of scales using a balance beam compares masses by balancing the force of gravity (weight) due to the mass of an object against the force due to gravity (weight) of a known mass. Either type of balance or scales can be calibrated to read in units of force (weight) such as Newtons, or in units of mass such as kilograms, but the balance or pair of scales using a traditional balance beam to compare masses will read correctly for mass even if moved to a place with a different (non-zero) gravitational field strength (but would then not read correctly if calibrated in units of force), while the spring balance would read correctly in force in a different gravitational feld strength (but would nor read correctly if calibrated in units of mass).
Menstrual cycle is the cycle of changes that occurs in the uterus and ovary for the purpose of sexual reproduction. It is essential for the production of eggs and for the preparation of the uterus for pregnancy. The menstrual cycle occurs only in fertile female humans and other female primates.
In humans, the length of a menstrual cycle varies greatly among women (ranging from 25 to 35 days), with 28 days designated as the average length. Each cycle can be divided into three phases based on events in the ovary (ovarian cycle) or in the uterus (uterine cycle). The ovarian cycle consists of the follicular phase, ovulation, and luteal phase whereas the uterine cycle is divided into menstruation, proliferative phase, and secretory phase. Both cycles are controlled by the endocrine system and the normal hormonal changes that occur can be interfered with using hormonal contraception to prevent reproduction.
Prenatal cocaine exposure (PCE) occurs when a pregnant woman uses cocaine and thereby exposes her fetus to the drug. "Crack baby" was a term coined to describe children who were exposed to crack (cocaine in smokable form) as fetuses; the concept of the crack baby emerged in the US during the 1980s and 1990s in the midst of a crack epidemic. Early studies reported that people who had been exposed to crack in utero would be severely emotionally, mentally, and physically disabled; this belief became common in the scientific and lay communities. Fears were widespread that a generation of crack babies were going to put severe strain on society and social services as they grew up. Later studies failed to substantiate the findings of earlier ones that PCE has severe disabling consequences; these earlier studies had been methodologically flawed (e.g. with small sample sizes and confounding factors). Scientists have come to understand that the findings of the early studies were vastly overstated and that most people who were exposed to cocaine in utero do not have disabilities.
No specific disorders or conditions have been found to result for people whose mothers used cocaine while pregnant. Studies focusing on children of six years and younger have not shown any direct, long-term effects of PCE on language, growth, or development as measured by test scores. PCE also appears to have little effect on infant growth. However, PCE is associated with premature birth, birth defects, attention deficit disorder, and other conditions. The effects of cocaine on a fetus are thought to be similar to those of tobacco and less severe than those of alcohol. No scientific evidence has shown a difference in harm to a fetus of crack and powder cocaine.