Unit Weight
Unit Weight - Related Videos
03:02
Measurement: Derived Units
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2020
The International System of Units or SI system, by international agreement, has fixed measurement units for seven fundamental properties: length, mass, time, temperature, electric current, amount of substance, and luminosity. These are called the SI base units. Units of measurement derived from the mathematical combination of SI base units are called SI-derived units. For example, the ratio of the SI unit for distance (meter; m) and the SI unit for time (second; s) gives the SI-derived unit...
00:57
Weighted Mean
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2023
While taking the arithmetic, geometric, or harmonic mean of a sample data set, equal importance is assigned to all the data points. However, all the values may not always be equally important in some data sets. An intrinsic bias might make it more important to give more weightage to specific values over others. For example, consider the number of goals scored in the matches of a tournament. While computing the average number of goals scored in the tournament, it may be more important to...
03:38
Measurement: Standard Units
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2020
Every measurement provides three kinds of information: the size or magnitude of the measurement (a number), a standard of comparison for the measurement (a unit), and an indication of the uncertainty of the measurement. While the number and unit are explicitly represented when a quantity is written, the uncertainty is an aspect of the errors in the measurement results. The number in the measurement can be represented in different ways, including decimal form and scientific notation, which is...
01:09
Apparent Weight
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2023
True weight is the measure of the gravitational force acting on an object. However, if the object accelerates, its measured weight is different from its true weight. Similar observations can be made when the object is submerged in water. An object's weight in water is its apparent weight, which is equal to the difference between its true weight and the buoyant forces. Consider a person standing on a bathroom scale inside an elevator. If the scale is accurate at rest, its reading equals the...
01:19
Mass and Weight
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2023
Mass and weight are often used interchangeably in everyday conversation. For example, medical records often show our weight in kilograms, but never in the correct units of newtons. In physics, however, there is an important distinction. Weight is the pull of the Earth on an object. It depends on the distance from the center of the Earth. Weight dramatically varies if we leave the Earth's surface, unlike mass, which does not vary with location. On the Moon, for example, the acceleration due to...
FAQs
Moisture increases the total weight of a soil mass while its measured volume may remain unchanged, so bulk unit weight rises as water is added. Dry unit weight excludes the water contribution and is therefore useful for comparing the solid framework of soils. Saturated unit weight represents conditions in which the voids are filled with water, supporting analyses of different field moisture states.
Void ratio describes the volume of empty spaces relative to the soil solids, while degree of saturation indicates how much of those spaces contains water. Changes in either condition alter the mass occupying a given volume and therefore change the reported value. Considering both variables helps engineers distinguish whether differences result from soil structure, water content, or incomplete saturation.
The appropriate form depends on the condition represented in the engineering calculation. Bulk unit weight reflects the material as found with its existing moisture, dry unit weight supports comparisons of compaction and soil structure, and saturated unit weight applies when voids are filled with water. Selecting the wrong condition can misrepresent the weight contributing to stresses or stability evaluations.
Unit weight supplies the material-weight component used to estimate overburden stress, the pressure created by soil above a reference depth. That stress affects related evaluations such as earth pressure, bearing capacity, slope stability, and settlement. Because moisture, void ratio, and saturation can change the selected value, engineers must match the input condition to the soil state being analyzed.
Measurement requires determining the total weight of a representative material quantity and the volume occupied by that quantity, then relating the two results. For soils and construction materials, the recorded condition should also identify relevant moisture or saturation state. Laboratory measurements provide controlled property values, while field testing helps determine whether the material matches expected construction conditions.
Engineers compare measured field values with laboratory or project expectations to judge whether placed material has achieved the required compaction condition. Dry unit weight is particularly useful because it focuses on the soil solids rather than changes caused only by added water. The comparison helps identify construction areas that may perform differently under structural or environmental loading.
Unit weight data supports design and assessment for soils, aggregates, concrete, and other construction materials. In geotechnical work, it contributes to calculations involving overburden stress, earth pressure, bearing capacity, slope stability, and settlement. Field and laboratory results also help engineers predict how materials will respond when moisture conditions or applied structural and environmental loads change.