Emilie Meyer
Balances are instruments that measure mass by comparing the weights of two bodies, usually for scientific purposes. The balance, also known as a beam balance or laboratory balance, is considered the first mass-measuring instrument ever invented. It consists of a pivoted horizontal lever with arms of equal length and a weighing pan suspended from each arm. The unknown mass is placed in one pan, and standard masses are added to the other until the beam is as close to equilibrium as possible. While scales also measure weight, they cannot measure mass directly as they are dependent on local gravity.
| Characteristics | Values |
|---|---|
| Traditional form | Pivoted horizontal lever with arms of equal length and a weighing pan suspended from each arm |
| Traditional use | Unknown mass is placed in one pan and standard masses are added to the other pan until the beam is as close to equilibrium as possible |
| Accuracy | A friction-free fulcrum, a pointer attached to the beam to amplify deviations, and the lever principle are used to achieve very precise measurements |
| Buoyancy | Allowance for buoyancy in air, depending on the densities of the masses involved, is needed for the greatest accuracy |
| Reference masses | An off-center beam can reduce the need for large reference masses, but it requires special reference masses and cannot be intrinsically checked for accuracy |
| Torsion balance | Utilizes pans that lie on top of a mechanical chamber that bases measurements on the twisting of a wire or fiber inside the chamber; can weigh objects greater than 120 mg with a margin of error of +/- 7 mg |
| Microbalance | Capable of making precise measurements of the mass of objects of relatively small mass, on the order of a million parts of a gram and below |
| Analytical balance | Designed to measure small mass in the sub-milligram range; the measuring pan is inside a transparent enclosure to prevent dust and air currents from affecting the balance's operation |
| Single-pan mechanical substitution balances | Maintain a constant load on the balance beam, achieving a consistent response throughout the useful capacity |
| Two-pan beam balance | Traditional symbol of Pyrrhonism, indicating the equal balance of arguments |
| Spring scales | Came into wide usage in the United Kingdom after 1840; postal workers could work more quickly with spring scales as they provided instantaneous readings |
| Balances vs. scales | Balances measure mass directly by comparing an unknown mass to a known mass, while scales measure weight, which is the force acting on a mass; scales are often used for larger masses, while balances are used for smaller masses |
| Electronic balances | Measure total mass and may also determine characteristics like average weight and moisture content |
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What You'll Learn
- The pan balance was the first mass-measuring instrument invented
- Balances measure mass by comparing unknown mass to a known mass
- Single-pan balances use one pan and adjustable weights to balance it
- Torsion balances are one of the most mechanically accurate analog balances
- Balances are used for precision measurement of mass
The pan balance was the first mass-measuring instrument invented
The pan balance, also known as a balance scale, beam balance, or laboratory balance, was the first mass-measuring instrument invented. It consists of a pivoted horizontal lever with arms of equal length, known as the beam or tron, and a weighing pan suspended from each arm. This is why the plural term "scales" is often used to refer to a weighing instrument.
To use the pan balance, an unknown mass is placed in one pan, and standard masses are added to the other pan until the beam reaches equilibrium. The position of a sliding mass moved along a graduated scale can also be used to determine a more accurate mass measurement. This type of balance is known as a precision balance.
The pan balance has a long history, with the earliest relics of weighing scales discovered in the Indus River Valley, dating back to around 2000 BC. These early devices consisted of two plates attached to an overhead beam fixed on a central pole, with weight stones added to balance the measured object. Similar devices have been excavated in China, dating back to the 3rd or 4th century BC, and there is evidence of their use by the ancient Egyptians as early as 5000 BC.
Over time, the design of the pan balance has evolved. The Romans introduced the use of a pin through the centre of the beam for the central bearing, improving the accuracy of measurements. In the 18th century, the invention of knife-edges led to the development of the modern mechanical balance, and by the end of the 19th century, the balance had become one of the world's most precise measuring devices.
Today, modern laboratory balances use electromagnetic force restoration (EMFR) to determine mass, by measuring the current required to oppose the weight of a sample lifted by an electromagnet. While digital and electronic scales have become more common, the traditional pan balance remains an important symbol of precision and measurement.
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Balances measure mass by comparing unknown mass to a known mass
Balances are instruments that measure mass, specifically the amount of matter in an object. They differ from scales, which measure weight, or the force acting on a mass that is equal to the object's mass times its acceleration due to gravity. Scales are often used to weigh larger masses, such as raw materials, reagents, and products in a production setting, as well as smaller masses in commercial or household settings.
A true balance measures mass by comparing an unknown mass to a known mass. This process is unaffected by changes in gravity, meaning a balance will give the same reading regardless of location. This is because gravity will act on both sides of the balance equally.
A balance scale, for example, operates on the principle of equilibrium, or balance and stability. It consists of a beam with a fulcrum at its centre and pans or plates at either end. To measure the mass of an object, you place it on one pan and then add known weights to the other pan until the beam is level. The mass of the object is then equal to the total mass of the known weights.
The balance (also known as a balance scale, beam balance, and laboratory balance) was the first mass-measuring instrument invented. It consists of a pivoted horizontal lever with arms of equal length (the beam or tron) and a weighing pan suspended from each arm. The unknown mass is placed in one pan, and standard masses are added to the other until the beam is as close to equilibrium as possible.
Modern lab balances work by Electromagnetic Force Restoration (EMFR) to determine the mass of a sample. The force of the sample is lifted by an electromagnet, and the current required to oppose the weight is measured.
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Single-pan balances use one pan and adjustable weights to balance it
A single-pan balance is a specific type of balance that employs a single pan for weighing objects. It is also known as a substitution balance because it determines an object's weight by substituting it with a known weight. This type of balance consists of a beam with two knife edges. One knife edge acts as a pivot, while the other supports the weighing pan. A fixed counterweight is located on the longer arm of the beam.
To measure the weight of an object using a single-pan balance, the object is first placed in the empty pan, and the beam is allowed to come to rest. Weights are then removed from the shorter arm until equilibrium is achieved. The weight of the object is determined by summing up the weights that were removed. Single-pan balances are less prone to errors caused by air currents and vibrations compared to two-pan balances, making them more accurate.
Single-pan balances are commonly used in educational, laboratory, or general weighing applications where high precision is not necessary. They are advantageous due to their simplicity, affordability, and ease of use. These balances do not require electricity or batteries and can provide accurate measurements for small to medium-sized objects. The weight capacity and readability can vary depending on the specific model and brand.
Calibration methods for single-pan balances may differ depending on the manufacturer's instructions. Typically, calibration involves placing known standard weights on the pan and adjusting the balance until the pointer indicates the correct weight. It is important to follow the manufacturer's guidelines for specific calibration procedures and to place the balance on a level surface during use.
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Torsion balances are one of the most mechanically accurate analog balances
A pan balance, also known as a balance scale, beam balance, or laboratory balance, is the first mass-measuring instrument ever invented. It consists of a pivoted horizontal lever with arms of equal length and a weighing pan suspended from each arm. The unknown mass is placed in one pan, and standard weights are added to the other pan until the beam is as close to equilibrium as possible.
The torsion balance consists of a rigid balance beam or a light aluminium bar suspended horizontally by a fine platinum wire, on which is mounted a small mirror. A small weight is fastened horizontally to one end of the bar, and an equal weight is suspended vertically from the other end by a platinum thread. The balance rotates under the influence of an unequal force of gravity acting on the two weights, causing a torque or twist in the supporting wire, to which the mirror is attached. The position of a beam of light cast by the mirror is observed by a small telescope or a photographic record, and the twisting force can be calculated.
Torsion balances are used to measure gravitational acceleration at the Earth's surface and have been employed to locate salt domes associated with petroleum deposits, iron ores, lead, zinc, copper, and tin ores, coal, and underground bodies of water. They can also be used to measure the flattening of the Earth and to test the theory of isostasy. Pharmacy schools in the U.S. still teach how to use torsion balances, and they are often used to weigh fractional gram values.
In summary, torsion balances are highly accurate analog devices that have been used for various scientific and industrial applications, especially in the field of geology and petroleum exploration. Their accuracy stems from their ability to measure gravitational forces and their sensitivity to changes in force, making them a valuable tool in various fields.
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Balances are used for precision measurement of mass
Balances are instruments that measure mass by comparing the weights of two bodies, usually for scientific purposes. This process is unaffected by changes in gravity, meaning that a balance will give the same reading irrespective of location. In traditional balances, this is achieved by placing an unknown mass in one pan and adding known masses to the other pan until the beam is as close to equilibrium as possible.
The balance, in its traditional form, was the first mass-measuring instrument invented. It consists of a pivoted horizontal lever with arms of equal length (the beam) and a weighing pan suspended from each arm. This is why weighing instruments are often referred to as "scales".
In precision balances, a more accurate determination of the mass is given by the position of a sliding mass moved along a graduated scale. For example, a decimal balance uses a lever in which the arm for weights is 10 times longer than the arm for weighted objects, allowing lighter weights to be used to weigh heavy objects.
By the end of the 19th century, the balance had become one of the world's most precise types of measuring devices. In the 20th century, electronic balances were developed, which used electrical compensation rather than mechanical deflection. These electronic systems can also measure characteristics such as average weight and moisture content.
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Frequently asked questions
A pan balance, also known as a beam balance, is a weighing instrument used to compare the weights of two bodies to determine the difference in mass. It consists of a pivoted horizontal lever with arms of equal length and a weighing pan suspended from each arm.
The unknown mass is placed in one pan, and standard masses are added to the other pan until the beam is as close to equilibrium as possible. The balance measures the weight of the object by comparing it to a known mass, and this process is not affected by changes in gravity.
There are several types of pan balances, including one-pan balances, torsion balances, and analytical balances. Torsion balances utilise pans that lie on top of a mechanical chamber, which bases measurements on the amount of twisting of a wire or fibre inside the chamber. Analytical balances have a measuring pan inside a transparent enclosure to prevent dust and air currents from affecting the balance's operation.
Pan balances can be very precise instruments. To improve accuracy, the balance's fulcrum should be friction-free, a pointer can be attached to the beam to amplify any deviations, and the lever principle can be used to apply fractional masses. Late 20th-century balances were electronic and more accurate than mechanical balances, and modern lab balances use Electromagnetic Force Restoration (EMFR) to determine mass.
