inertial massgravitational massweight
Proportionality, by definition, implies that two values have a constant ratio: An early use of this relationship is a balance scale, which balances the force of one object's weight against the force of another object's weight. The two sides of a balance scale are close enough that the objects experience similar gravitational fields. Hence, if they have similar masses then their weights will also be similar. This allows the scale, by comparing weights, to also compare masses. Consequently, historical weight standards were often defined in terms of amounts. The Romans, for example, used the carob seed (carat or siliqua) as a measurement standard.


obesemorbidly obeseoverweight
Obesity is a medical condition in which excess body fat has accumulated to the extent that it may have an adverse effect on health. It is defined by body mass index (BMI) and further evaluated in terms of fat distribution via the waist–hip ratio and total cardiovascular risk factors. BMI is closely related to both percentage body fat and total body fat. In children, a healthy weight varies with age and sex. Obesity in children and adolescents is defined not as an absolute number but in relation to a historical normal group, such that obesity is a BMI greater than the 95th percentile.

Body composition

fat free massbody composition monitorsfat-free mass
The primary exercises needed to improve body composition involve fat burning and cardiovascular exercises. 1) Take measurements on the right side of the body. 2) Mark client up. 3) Pinch skin (KM) above mark. 4) Pull fat away from muscles. 5) Place caliper halfway between top and bottom of mark. 6) Allow caliper to settle (1–2 seconds). 7) Take reading – repeat 15 seconds. 8) Add up total (4) – average. 9) Calculate body fat %. Body volume index. Body mass index.

Classification of obesity

Body Volume Indexbody mass indexBVI
BMI can be used to predict the risk of metabolic abnormalities like diabetes. Body mass index or BMI is a simple and widely used method for estimating body fat mass. BMI was developed in the 19th century by the Belgian statistician and anthropometrist Adolphe Quetelet. BMI is an accurate reflection of body fat percentage in the majority of the adult population. However it is less accurate in people such as body builders and pregnant women. A formula combining BMI, age, and gender can be used to estimate a person's body fat percentage to an accuracy of 4%.

Relative Fat Mass

Body mass index (BMI). Body fat percentage (BFP). Body water (TBW). Corpulence index (CI). Human heart age.

Human body weight

body massbody weightweight
Body Mass Index (BMI). Body volume index. Hesse's Rule. History of anthropometry. Human height. List of the heaviest people. Obesity. Emaciation. Overweight. Underweight. Weight loss and weight gain. Weight phobia.


One device for measuring weight or mass is called a weighing scale or, often, simply a scale. A spring scale measures force but not mass, a balance compares weight, both require a gravitational field to operate. Some of the most accurate instruments for measuring weight or mass are based on load cells with a digital read-out, but require a gravitational field to function and would not work in free fall. The measures used in economics are physical measures, nominal price value measures and real price measures. These measures differ from one another by the variables they measure and by the variables excluded from measurements.

Spring scale

spring balancespring scales
A spring scale or spring balance or newton meter is a type of weighing scale. It consists of spring fixed at one end with a hook to attach an object at the other. It works by Hooke's Law, which states that the force needed to extend a spring is proportional to the distance that spring is extended from its rest position. Therefore, the scale markings on the spring balance are equally spaced. A spring scale cannot measure mass, only weight.


Because at any given point on Earth the weight of an object is proportional to its mass, the mass of an object in kilograms is usually measured by comparing its weight to the weight of a standard mass, whose mass is known in kilograms, using a device called a weighing scale. The ratio of the force of gravity on the two objects, measured by the scale, is equal to the ratio of their masses. On April 7, 1795, the gram was decreed in France to be "the absolute weight of a volume of pure water equal to the cube of the hundredth part of the metre, and at the temperature of melting ice".


digital multimeterdigital multimetersmultitester
Standard analog multimeters measure with typically ±3% accuracy, though instruments of higher accuracy are made. Standard portable digital multimeters are specified to have an accuracy of typically ±0.5% on the DC voltage ranges. Mainstream bench-top multimeters are available with specified accuracy of better than ±0.01%. Laboratory grade instruments can have accuracies of a few parts per million. Accuracy figures need to be interpreted with care. The accuracy of an analog instrument usually refers to full-scale deflection; a measurement of 30 V on the 100 V scale of a 3% meter is subject to an error of 3 V, 10% of the reading.

Chemical reaction

reactionchemical reactionsreactions
An important class of redox reactions are the electrochemical reactions, where electrons from the power supply are used as the reducing agent. These reactions are particularly important for the production of chemical elements, such as chlorine or aluminium. The reverse process in which electrons are released in redox reactions and can be used as electrical energy is possible and used in batteries. In complexation reactions, several ligands react with a metal atom to form a coordination complex. This is achieved by providing lone pairs of the ligand into empty orbitals of the metal atom and forming dipolar bonds.


tangent galvanometernull detectorgalvanoscope
Because the pointer of the meter is usually a small distance above the scale of the meter, parallax error can occur when the operator attempts to read the scale line that "lines up" with the pointer. To counter this, some meters include a mirror along the markings of the principal scale. The accuracy of the reading from a mirrored scale is improved by positioning one's head while reading the scale so that the pointer and the reflection of the pointer are aligned; at this point, the operator's eye must be directly above the pointer and any parallax error has been minimized.


corrosion resistancecorrodecorrosive
It is the gradual destruction of materials (usually metals) by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and stopping corrosion. In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfates. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal, and results in a distinctive orange colouration.

Contact electrification

contact tensioncontact potentialcontact electricity
In the late 18th century, scientists developed sensitive instruments for detecting 'electrification', otherwise known as electrostatic charge imbalance. The phenomenon of electrification by contact, or contact tension, was quickly discovered. When two objects were touched together, sometimes the objects became spontaneously charged. One object developed a net negative charge, while the other developed an equal and opposite positive charge. Then it was discovered that 'piles' of dissimilar metal disks separated by acid-soaked cloth, Voltaic piles, could also produce charge differences.

Gouy balance

Since it requires a large and powerful electromagnet, the Gouy balance is a stationary instrument permanently set up on a bench. The apparatus is often placed on a marble balance table in a non-ventilated room to minimize the vibrations and disruption from the environment. The stationary magnetic of a Gouy balance is often an electromagnet connected to a power source, since balance recordings with and without the applied magnetic field are required of the procedure. m b – m a = apparent difference in mass. g = gravitational acceleration. K 1 = volume susceptibility of medium, usually air and of negligible value. K 2 = volume susceptibility of sample. H = applied magnetic field.


Musical tuning – tuning, in music, means calibrating musical instruments into playing the right pitch. Precision measurement equipment laboratory. Scale test car – a device used to calibrate weighing scales that weigh railroad cars. Systems of measurement.

Mass versus weight

weightdistinctionhistorical conflation of mass and weight
Whenever a high-precision scale (or balance) in routine laboratory use is calibrated using stainless steel standards, the scale is actually being calibrated to conventional mass; that is, true mass minus 150 ppm of buoyancy. Since objects with precisely the same mass but with different densities displace different volumes and therefore have different buoyancies and weights, any object measured on this scale (compared to a stainless steel mass standard) has its conventional mass measured; that is, its true mass minus an unknown degree of buoyancy. In high-accuracy work, the volume of the article can be measured to mathematically null the effect of buoyancy.

Adipose tissue

adiposebody fatfat
A body fat meter is a widely available tool used to measure the percentage of fat in the human body. Different meters use various methods to determine the body fat to weight ratio. They tend to under-read body fat percentage. In contrast with clinical tools, one relatively inexpensive type of body fat meter uses the principle of bioelectrical impedance analysis (BIA) in order to determine an individual's body fat percentage. To achieve this, the meter passes a small, harmless, electric current through the body and measures the resistance, then uses information on the person's weight, height, age, and sex to calculate an approximate value for the person's body fat percentage.


Electrochemical series. Electrochemistry. Electrolysis. Electron equivalent. Electron transport chain. Electrosynthesis. Galvanic cell. Hydrogenation. Membrane potential. Microbial fuel cell. Nucleophilic abstraction. Organic redox reaction. Oxidative addition and reductive elimination. Oxidative phosphorylation. Partial oxidation. Pro-oxidant. Reduced gas. Reducing agent. Reducing atmosphere. Reduction potential. Thermic reaction. Transmetalation. Chemical Equation Balancer – An open source chemical equation balancer that handles redox reactions. Redox reactions calculator. Redox reactions at Chemguide.


excess body weightexcess weightheavy-set
Body mass index. The body mass index (BMI) is a measure of a person's weight taking into account their height. It is given by the following formula: BMI equals a person's weight (mass) in kilograms divided by the square of the person's height in metres. The units therefore are kg/m 2 but BMI measures are typically used and written without units. BMI provides a significantly more accurate representation of body fat content than simply measuring a person's weight. It is only moderately correlated with both body fat percentage and body fat mass (R 2 of 0.68).

Waist–hip ratio

waist-hip ratiowaist-to-hip ratiowaist to hip ratio
The body fat percentage is considered to be an even more accurate measure of relative weight. Of these three measurements, only the waist-hip ratio takes account of the differences in body structure. Hence, it is possible for two women to have vastly different body mass indices but the same waist–hip ratio, or to have the same body mass index but vastly different waist-hip ratios. WHR has been shown to be a better predictor of cardiovascular disease than waist circumference and body-mass index. However, other studies have found waist circumference, not WHR, to be a good indicator of cardiovascular risk factors, body fat distribution, and hypertension in type 2 diabetes.

Waist-to-height ratio

waist-to-height ratio WHtR
As a comparative, the following table categorises the boundaries of persons in terms of health: * WHtR Calculator Body fat percentage. Body water. Allometric law. Ponderal index.


Electrochemistry has always been an important part of electricity. From the initial invention of the Voltaic pile, electrochemical cells have evolved into the many different types of batteries, electroplating and electrolysis cells. Aluminium is produced in vast quantities this way, and many portable devices are electrically powered using rechargeable cells. An electric circuit is an interconnection of electric components such that electric charge is made to flow along a closed path (a circuit), usually to perform some useful task. The components in an electric circuit can take many forms, which can include elements such as resistors, capacitors, switches, transformers and electronics.

Electric charge

chargechargedelectrical charge
A measure of charge should be a multiple of the elementary charge e, even if at large scales charge seems to behave as a real quantity. In some contexts it is meaningful to speak of fractions of a charge; for example in the charging of a capacitor, or in the fractional quantum Hall effect. The unit faraday is sometimes used in electrochemistry. One faraday of charge is the magnitude of the charge of one mole of electrons, i.e. 96485.33289(59) C.