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If, on the other hand, they have the opposite charge, where one is positive and one is negative, they are attracted to each other. This movement of particles, which are repelled or attracted to other particles, is electricity — a physical phenomenon which we use in daily lives and in most of technology. The electromagnetic force can account for chemical reactions, light, and electricity, as well as interactions between molecules, atoms, and electrons.
These interactions between particles are responsible for the shapes that solid objects take in the world. The electromagnetic force prevents two solid objects from permeating each other, because the electrons in one object repel the electrons of the same charge of the other object. Historically electric and magnetic forces were treated as separate influences, but eventually it was discovered that they are related. Most objects have neutral charge, but it is possible to change the charge of an object by rubbing two objects together.
The electrons will travel between the two materials, being attracted to the opposite charged electrons in the other material. This will leave more of the same charge electrons on the surface of each object, thus changing the dominant charge of the object overall. This is because electrons on the surface of the hair are attracted more to the atoms on the surface of the sweater than electrons on the surface of the sweater are attracted to the atoms on the surface of the hair.
Hair or other similarly charged objects will also be attracted to the neutrally charged surfaces as well. Weak Force Weak force is weaker than the electromagnetic one. Just like gluons carry the strong force, W and Z bosons carry the weak force. They are elementary particles that are emitted or absorbed. W bosons facilitate the process of radioactive decay, while the Z bosons do not affect the particles that they come in contact with, other than transferring momentum.
Carbon dating, a process of determining the age of organic matter, is possible because of the weak force. It is used to establish the age of historical artifacts, and is based on evaluating the decay of carbon present in this organic matter. Gravitational Force Lake Ontario. Starry Night Gravitational force is the weakest of the four.
It keeps the astronomical objects in their positions in the universe, is responsible for tides, and causes objects to fall on the ground when released. It is the force that acts upon objects, attracting them to each other.
Like the other forces, it is believed to be mediated by particles, gravitons, but these particles have not been detected yet. Gravitation affects how astronomical objects move, and the motion can be calculated, based on the mass of the surrounding objects.
This dependency allowed scientists to predict that Neptune exists by watching the motion of Uranus, before Neptune was seen in the telescope. This was because the movement of Uranus was inconsistent with its predicted motion, based on the astronomical objects known at the time, therefore scientists deducted that another planet, yet unseen, must be affecting its movement patterns. According to the theory of relativity, gravity also changes the spacetime continuum, the four dimensional space that everything, including humans, exist in.
According to this theory, the curvature of spacetime increases with mass, and because of that it is easier to notice with objects as large as planets or greater in mass.
This curvature was proved experimentally, and can be seen when two synchronized clocks are compared, where one is stationary and one moves for a considerable distance along a body with large mass. For example, if the clock is moved around the orbit of the earth, as in Hafele—Keating experiment, then the time it shows will be behind the stationary clock, because the spacetime curvature causes the time to run slower for the clock in motion.
The force of gravity causes objects to accelerate when falling towards another object, and this is noticeable when the difference in mass between the two is great. This acceleration can be calculated based on the mass of the objects. For objects falling towards the Earth it is about 9. Tides Sea rocks Tides are examples of gravitational force in action. They are caused by the gravitational forces of the Moon, the Sun, and the Earth. Contrast to solid objects, water can change shape easily when forces act upon it.
Therefore when gravitational forces of the Moon and the Sun act upon the Earth, the ground surface does not get pulled by these forces as much as the water does.
The Moon and the Sun move across the sky, and the water on Earth follows them, causing tides. The forces that act upon the water are called tidal forces; they are a variety of gravitational forces. The Moon, being closer to the Earth, has a stronger tidal force compared to the Sun.
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When the tidal forces of the Sun and the Moon act in the same direction, the tide is the strongest and is called spring tide. When these two forces are in opposition, the tide is the weakest and is called a neap tide. Tides happen with different frequency depending on the geographical area. Because gravity of the Moon and the Sun pulls both the water and the entire planet Earth, in some areas tides occur both when the gravitational force pulls the water and the Earth in the same or in different directions.
In this case the high and low tide pair happens twice in one day. In some areas this happens only once a day.
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Tide patterns on the coast depend on the shape of the coast, the deep ocean tide patterns, and the location of the Moon and the Sun, as well as the interaction of their gravitational forces. In some locations, the duration of time between tides can last up to several years. Depending on the coastline and the depth of the ocean, tides can cause currents, storms, changes in wind patterns, and fluctuation in air pressure. Some places use special clocks to calculate when the next tide will happen.
They are configured based on the tidal occurrences in the area, and need to be reconfigured when moved to another location. In some areas tide clocks are not effective because tides cannot be predicted easily there. The tidal force which moves water to and from the shore is sometimes used to generate power.
Tidal mills have used this force for centuries.
The basic construction has a water reservoir, and the water is let in at high tide and out at low tide. The kinetic energy of the flowing water moves the wheel of the mill, and the generated power is used to perform work, for example, grinding grains into flour. Next to be affected is the SI unit of powerthe wattwhich is one joule per second. The ampere too is defined relative to the newton.
With the magnitude of the primary units of electricity thus determined by the kilogram, so too follow many others, namely the coulombvoltteslaand weber. Because the magnitude of many of the units comprising the SI system of measurement is ultimately defined by the mass of a year-old, golf-ball-sized piece of metal, the quality of the IPK must be diligently protected to preserve the integrity of the SI system. Yet, despite the best stewardship, the average mass of the worldwide ensemble of prototypes and the mass of the IPK have likely diverged another 6.
Fortunately, definitions of the SI units are quite different from their practical realizations. Now suppose that the official measurement of the second was found to have drifted by a few parts per billion it is actually extremely stable with a reproducibility of a few parts in Scientists performing metre calibrations would simply continue to measure out the same number of laser wavelengths until an agreement was reached to do otherwise.
The same is true with regard to the real-world dependency on the kilogram: Any discrepancy would eventually have to be reconciled though, because the virtue of the SI system is its precise mathematical and logical harmony amongst its units.
If the IPK's value were definitively proven to have changed, one solution would be to simply redefine the kilogram as being equal to the mass of the IPK plus an offset value, similarly to what is currently done with its replicas; e. The long-term solution to this problem, however, is to liberate the SI system's dependency on the IPK by developing a practical realization of the kilogram that can be reproduced in different laboratories by following a written specification.
The units of measure in such a practical realization would have their magnitudes precisely defined and expressed in terms of fundamental physical constants. While major portions of the SI system would still be based on the kilogram, the kilogram would in turn be based on invariant, universal constants of nature.
Redefinition agreed on 16 November [ edit ] Main articles: This approach effectively defines the kilogram in terms of the second and the metre, and will take effect in Inthe metrepreviously similarly having been defined with reference to a single platinum-iridium bar with two marks on it, was redefined in terms of an invariant physical constant the wavelength of a particular emission of light emitted by krypton and later the speed of light so that the standard can be independently reproduced in different laboratories by following a written specification.
The Kibble balance discussed below is one way do this. As part of this project, a variety of very different technologies and approaches were considered and explored over many years. They too are covered below. Some of these now-abandoned approaches were based on equipment and procedures that would have enabled the reproducible production of new, kilogram-mass prototypes on demand albeit with extraordinary effort using measurement techniques and material properties that are ultimately based on, or traceable to, physical constants.
Others were based on devices that measured either the acceleration or weight of hand-tuned kilogram test masses and which expressed their magnitudes in electrical terms via special components that permit traceability to physical constants.
All approaches depend on converting a weight measurement to a mass, and therefore require the precise measurement of the strength of gravity in laboratories.
All approaches would have precisely fixed one or more constants of nature at a defined value. The vacuum chamber dome, which lowers over the entire apparatus, is visible at top. Kibble balance The Kibble balance known as a "watt balance" before is essentially a single-pan weighing scale that measures the electric power necessary to oppose the weight of a kilogram test mass as it is pulled by Earth's gravity. It is a variation of an ampere balancewith an extra calibration step that eliminates the effect of geometry.
The electric potential in the Kibble balance is delineated by a Josephson voltage standardwhich allows voltage to be linked to an invariant constant of nature with extremely high precision and stability.
Its circuit resistance is calibrated against a quantum Hall effect resistance standard.
The Kibble balance requires extremely precise measurement of the local gravitational acceleration g in the laboratory, using a gravimeter. The local gravitational acceleration g is measured with exceptional precision with the help of a laser interferometer. The laser's pattern of interference fringes —the dark and light bands above—blooms at an ever-faster rate as a free-falling corner reflector drops inside an absolute gravimeter. The pattern's frequency sweep is timed by an atomic clock.HOW TO CONVERT KILOGRAMS TO POUND (Kg TO lb ) AND POUNDS TO KILOGRAM(lb to kg)
Gravity and the nature of the Kibble balance, which oscillates test masses up and down against the local gravitational acceleration g, are exploited so that mechanical power is compared against electrical power, which is the square of voltage divided by electrical resistance.
There are also slight seasonal variations in g at a location due to changes in underground water tables, and larger semimonthly and diurnal changes due to tidal distortions in the Earth's shape caused by the Moon and the Sun.
Although g would not be a term in the definition of the kilogram, it would be crucial in the process of measurement of the kilogram when relating energy to power.
Accordingly, g must be measured with at least as much precision and accuracy as are the other terms, so measurements of g must also be traceable to fundamental constants of nature.
For the most precise work in mass metrology, g is measured using dropping-mass absolute gravimeters that contain an iodine-stabilized helium—neon laser interferometer.
The fringe-signalfrequency-sweep output from the interferometer is measured with a rubidium atomic clock. Since this type of dropping-mass gravimeter derives its accuracy and stability from the constancy of the speed of light as well as the innate properties of helium, neon, and rubidium atoms, the 'gravity' term in the delineation of an all-electronic kilogram is also measured in terms of invariants of nature—and with very high precision.
It would free physicists from the need to rely on assumptions about the stability of those prototypes. Instead, hand-tuned, close-approximation mass standards would simply be weighed and documented as being equal to one kilogram plus an offset value. With the Kibble balance, while the kilogram would be delineated in electrical and gravity terms, all of which are traceable to invariants of nature; it would be defined in a manner that is directly traceable to three fundamental constants of nature.
The Planck constant defines the kilogram in terms of the second and the metre. By fixing the Planck constant, the definition of the kilogram would in addition depend only on the definitions of the second and the metre.
The definition of the second depends on a single defined physical constant: The metre depends on the second and on an additional defined physical constant: Once the kilogram is redefined in this manner, physical objects such as the IPK will no longer be part of the definition, but will instead become transfer standards.
Scales like the Kibble balance also permit more flexibility in choosing materials with especially desirable properties for mass standards. This would reduce the relative uncertainty when making mass comparisons in air. Alternatively, entirely different materials and constructions could be explored with the objective of producing mass standards with greater stability.
For instance, osmium -iridium alloys could be investigated if platinum's propensity to absorb hydrogen due to catalysis of VOCs and hydrocarbon-based cleaning solvents and atmospheric mercury proved to be sources of instability. Also, vapor-deposited, protective ceramic coatings like nitrides could be investigated for their suitability for chemically isolating these new alloys. The challenge with Kibble balances is not only in reducing their uncertainty, but also in making them truly practical realizations of the kilogram.
Nearly every aspect of Kibble balances and their support equipment requires such extraordinarily precise and accurate, state-of-the-art technology that—unlike a device like an atomic clock—few countries would currently choose to fund their operation. For instance, the NIST's Kibble balance used four resistance standards ineach of which was rotated through the Kibble balance every two to six weeks after being calibrated in a different part of NIST headquarters facility in Gaithersburg, Maryland.
When the new definition takes effect, it is likely there will only be a few—at most—Kibble balances initially operating in the world. Alternative approaches to redefining the kilogram[ edit ] Several alternative approaches to redefining the kilogram that were fundamentally different from the Kibble balance were explored to varying degrees, with some abandoned.
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The Avogadro project, in particular, was important for the redefinition decision because it provided an accurate measurement of the Planck constant that was consistent with and independent of the Kibble balance method. These spheres are among the roundest man-made objects in the world. If the best of these spheres were scaled to the size of Earth, its high point—a continent-size area—would rise to a maximum elevation of 2.
Silicon was chosen because a commercial infrastructure with mature processes for creating defect-free, ultra-pure monocrystalline silicon already exists to service the semiconductor industry. To make a practical realization of the kilogram, a silicon boule a rod-like, single-crystal ingot would be produced.
Its isotopic composition would be measured with a mass spectrometer to determine its average relative atomic mass. The boule would be cut, ground, and polished into spheres. The size of a select sphere would be measured using optical interferometry to an uncertainty of about 0.
This permits its atomic spacing to be determined with an uncertainty of only three parts per billion. With the size of the sphere, its average atomic mass, and its atomic spacing known, the required sphere diameter can be calculated with sufficient precision and low uncertainty to enable it to be finish-polished to a target mass of one kilogram.
Experiments are being performed on the Avogadro Project's silicon spheres to determine whether their masses are most stable when stored in a vacuum, a partial vacuum, or ambient pressure. Balances can only compare the mass of a silicon sphere to that of a reference mass. Given the latest understanding of the lack of long-term mass stability with the IPK and its replicas, there is no known, perfectly stable mass artefact to compare against.
Single-pan scaleswhich measure weight relative to an invariant of nature, are not precise to the necessary long-term uncertainty of 10—20 parts per billion. Another issue to be overcome is that silicon oxidizes and forms a thin layer equivalent to 5—20 silicon atoms deep of silicon dioxide quartz and silicon monoxide. This layer slightly increases the mass of the sphere, an effect that must be accounted for when polishing the sphere to its finished size. Oxidation is not an issue with platinum and iridium, both of which are noble metals that are roughly as cathodic as oxygen and therefore don't oxidize unless coaxed to do so in the laboratory.