![]() Weight - Wikipedia. This page is about the physical concept. ![]() ![]() ![]() ![]() In law, commerce, and in colloquial usage weight may also refer to mass. For other uses see weight (disambiguation). In science and engineering, the weight of an object is usually taken to be the force on the object due to gravity. The unit of measurement for weight is that of force, which in the International System of Units (SI) is the newton. For example, an object with a mass of one kilogram has a weight of about 9. Earth, and about one- sixth as much on the Moon. In this sense of weight, a body can be weightless only if it is far away (in principle infinitely far away) from any other mass. Although weight and mass are scientifically distinct quantities, the terms are often confused with each other in everyday use (i. There the weight is a measure of the magnitude of the reaction force exerted on a body. Typically, in measuring an object's weight, the object is placed on scales at rest with respect to the earth, but the definition can be extended to other states of motion. Thus, in a state of free fall, the weight would be zero. In this second sense of weight, terrestrial objects can be weightless. Ignoring air resistance, the famous apple falling from the tree, on its way to meet the ground near Isaac Newton, is weightless. Further complications in elucidating the various concepts of weight have to do with the theory of relativity according to which gravity is modelled as a consequence of the curvature of spacetime. In the teaching community, a considerable debate has existed for over half a century on how to define weight for their students. The current situation is that a multiple set of concepts co- exist and find use in their various contexts. These were typically viewed as inherent properties of objects. Plato described weight as the natural tendency of objects to seek their kin. To Aristotle weight and levity represented the tendency to restore the natural order of the basic elements: air, earth, fire and water. He ascribed absolute weight to earth and absolute levity to fire. Archimedes saw weight as a quality opposed to buoyancy, with the conflict between the two determining if an object sinks or floats. The first operational definition of weight was given by Euclid, who defined weight as: . As medieval scholars discovered that in practice the speed of a falling object increased with time, this prompted a change to the concept of weight to maintain this cause effect relationship. Weight was split into a . The concept of gravitas was eventually replaced by Jean Buridan's impetus, a precursor to momentum. In the 1. 7th century, Galileo made significant advances in the concept of weight. Weight loss seems easy but, if it were, none of us would have a weight problem. Get the basics for how to calculate your BMR and activity calories while finding ways. Tools: Formula Weight Calculator: Putting in a molecular formula of any type such as K2Cr2O7, CH3CH2COOH, KFe Weight Loss Percent Vs. While it's easy to figure out your percentage of weight loss, not all of that weight necessarily comes from fat.![]() He proposed a way to measure the difference between the weight of a moving object and an object at rest. Ultimately, he concluded weight was proportionate to the amount of matter of an object, and not the speed of motion as supposed by the Aristotelean view of physics. ![]() Weight became fundamentally separate from mass. Mass was identified as a fundamental property of objects connected to their inertia, while weight became identified with the force of gravity on an object and therefore dependent on the context of the object. In particular, Newton considered weight to be relative to another object causing the gravitational pull, e. This allowed him to consider concepts as true position and true velocity. ![]()
He considered this a false weight induced by imperfect measurement conditions, for which he introduced the term apparent weight as compared to the true weight defined by gravity. This led the 3rd General Conference on Weights and Measures (CGPM) of 1. Einstein's principle of equivalence put all observers, moving or accelerating, on the same footing. This led to an ambiguity as to what exactly is meant by the force of gravity and weight. A scale in an accelerating elevator cannot be distinguished from a scale in a gravitational field. ![]() ![]() Gravitational force and weight thereby became essentially frame- dependent quantities. This prompted the abandonment of the concept as superfluous in the fundamental sciences such as physics and chemistry. Nonetheless, the concept remained important in the teaching of physics. The ambiguities introduced by relativity led, starting in the 1. This is a horizontal acceleration of 5. Combined with the vertical g- force in the stationary case the Pythagorean theorem yields a g- force of 5. It is this g- force that causes the driver's weight if one uses the operational definition. If one uses the gravitational definition, the driver's weight is unchanged by the motion of the car. Several definitions exist for weight, not all of which are equivalent. However, some textbooks also take weight to be a scalar by defining. Sometimes, it is simply taken to have a standard value of 9. On the Moon, an object would give a lower reading. Right: A balance scale indirectly measures mass, by comparing an object to references. On the Moon, an object would give the same reading, because the object and references would both become lighter. Operational definition. So, there exists opposite and equal force by the support on the body. Also it is equal to the force exerted by the body on its support because action and reaction have same numerical value and opposite direction. This can make a considerable difference, depending on the details; for example, an object in free fall exerts little if any force on its support, a situation that is commonly referred to as weightlessness. However, being in free fall does not affect the weight according to the gravitational definition. Therefore, the operational definition is sometimes refined by requiring that the object be at rest. In the operational definition, the weight of an object at rest on the surface of the Earth is lessened by the effect of the centrifugal force from the Earth's rotation. The operational definition, as usually given, does not explicitly exclude the effects of buoyancy, which reduces the measured weight of an object when it is immersed in a fluid such as air or water. As a result, a floating balloon or an object floating in water might be said to have zero weight. ISO definition. When the chosen frame is co- moving with the object in question then this definition precisely agrees with the operational definition. This is usually referred to as the apparent weight of the object. A common example of this is the effect of buoyancy, when an object is immersed in a fluid the displacement of the fluid will cause an upward force on the object, making it appear lighter when weighed on a scale. When the gravitational definition of weight is used, the operational weight measured by an accelerating scale is often also referred to as the apparent weight. Notice that the amount of force that the table is pushing upward on the object (the N vector) is equal to the downward force of the object's weight (shown here as mg, as weight is equal to the object's mass multiplied with the acceleration due to gravity): because these forces are equal, the object is in a state of equilibrium (all the forces and moments acting on it sum to zero). In modern scientific usage, weight and mass are fundamentally different quantities: mass is an . However, in most practical everyday situations the word . In a uniform gravitational field, the gravitational force exerted on an object (its weight) is directly proportional to its mass. For example, object A weighs 1. B, so therefore the mass of object A is 1. B. This means that an object's mass can be measured indirectly by its weight, and so, for everyday purposes, weighing (using a weighing scale) is an entirely acceptable way of measuring mass. Similarly, a balance measures mass indirectly by comparing the weight of the measured item to that of an object(s) of known mass. Since the measured item and the comparison mass are in virtually the same location, so experiencing the same gravitational field, the effect of varying gravity does not affect the comparison or the resulting measurement. The Earth's gravitational field is not uniform but can vary by as much as 0. These variations alter the relationship between weight and mass, and must be taken into account in high precision weight measurements that are intended to indirectly measure mass. Spring scales, which measure local weight, must be calibrated at the location at which the objects will be used to show this standard weight, to be legal for commerce. The gravity on the surface of the Moon is only about one- sixth as strong as on the surface of the Earth. A one- kilogram mass is still a one- kilogram mass (as mass is an extrinsic property of the object) but the downward force due to gravity, and therefore its weight, is only one- sixth of what the object would have on Earth. So a man of mass 1. Moon. SI units. The SI unit of weight is the same as that of force: the newton (N) . Used in this sense, the proper SI unit is the kilogram (kg). The poundal is defined as the force necessary to accelerate an object of one- pound mass at 1 ft/s. The slug is defined as the amount of mass that accelerates at 1 ft/s. The kilogram- force is a non- SI unit of force, defined as the force exerted by a one kilogram mass in standard Earth gravity (equal to 9. The dyne is the cgs unit of force and is not a part of SI, while weights measured in the cgs unit of mass, the gram, remain a part of SI. Sensation. A spring scale or hydraulic or pneumatic scale measures local weight, the local force of gravity on the object (strictly apparent weight force). Since the local force of gravity can vary by up to 0. To standardize weights, scales are always calibrated to read the weight an object would have at a nominal standard gravity of 9. However, this calibration is done at the factory. When the scale is moved to another location on Earth, the force of gravity will be different, causing a slight error. So to be highly accurate, and legal for commerce, spring scales must be re- calibrated at the location at which they will be used.
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