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| Physics Question - ma = mg |
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| CatalinaWOW:
From Wikipedia which has the references. I apologize I did forget to subscript the value properly. The article mentions that this is common The standard acceleration due to gravity (or standard acceleration of free fall), sometimes abbreviated as standard gravity, usually denoted by ɡ0 or ɡn, is the nominal gravitational acceleration of an object in a vacuum near the surface of the Earth. It is defined by standard as 9.80665 m/s2 (about 32.17405 ft/s2). This value was established by the 3rd CGPM (1901, CR 70) and used to define the standard weight of an object as the product of its mass and this nominal acceleration.[1][2] The acceleration of a body near the surface of the Earth is due to the combined effects of gravity and centrifugal acceleration from the rotation of the Earth (but the latter is small enough to be negligible for most purposes); the total (the apparent gravity) is about 0.5% greater at the poles than at the Equator.[3][4] Although the symbol ɡ is sometimes used for standard gravity, ɡ (without a suffix) can also mean the local acceleration due to local gravity and centrifugal acceleration, which varies depending on one's position on Earth (see Earth's gravity). The symbol ɡ should not be confused with G, the gravitational constant, or g, the symbol for gram. The ɡ is also used as a unit for any form of acceleration, with the value defined as above; see g-force. The value of ɡ0 defined above is a nominal midrange value on Earth, originally based on the acceleration of a body in free fall at sea level at a geodetic latitude of 45°. Although the actual acceleration of free fall on Earth varies according to location, the above standard figure is always used for metrological purposes. In particular, it gives the conversion factor between newton and kilogram-force, two units of force. |
| TimFox:
The information in this Wikipedia article is consistent with that I quoted from Halliday and Resnick. Specifically, adding a subscript to g indicates that is measured in a specified location, while I insist that "g" is a general term for the parameter in different locations. Luckily, we need not worry about this in metrology when we use SI units. |
| CatalinaWOW:
I will also give the example describing aircraft and spacecraft accelerations in g's. In this usage the g is always a standard gravity. And this usage is rarely, if ever, used where precision is required. But the g is a relatable unit, requiring less mental gymnastics than saying that most pilots lose consciousness somewhere in the neighborhood of 59 to 69 meters per second squared. |
| CatalinaWOW:
--- Quote from: TimFox on June 29, 2021, 06:46:40 pm ---The information in this Wikipedia article is consistent with that I quoted from Halliday and Resnick. Luckily, we need not worry about this in metrology when we use SI units. --- End quote --- As I read the documents from BIPM, in metrology you don't use g in any of its connotations in metrology. Only units traceable to standard distance and time. The only traceability chains authorized are direct tracing to distance and time, comparison to a reference gravitometer which has used the first method, or comparison to an acceleration value at a specific location measured by a gravitometer that has been calibrated by one of the first two methods. The use of g (in any of its forms) is a convenience for practitioners in any number of fields. Again, horses for courses. |
| TimFox:
In that case, as you properly stated it, "g" is not italic, since it is a unit of measurement, while g is a parameter, equal to the magnitude of the vector g. When subjected to an acceleration of 10 g along the vertical direction, the victim will weigh 11 times his normal weight. In college, I did measure g (in southern Minnesota), using a Kater pendulum. In the ancient textbooks, before electronic timers, the period was measured by placing the Kater pendulum in front of a grandfather clock's pendulum and observing the beat frequency. In 1969, I used an -hp- 520 vacuum-tube counter, with Nixie tube readout, that was roughly 19 inches cubed, and a simple photocell. |
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