Talk:Orders of magnitude (acceleration)

this page reports that parachutists experience 33 Gs, but the citation is highly questionable and should be double-checked 74.111.225.136 (talk) 01:31, 18 August 2014 (UTC)

This page is lacking the negative ( tiny ) acceleration orders of magnitude. itsme (talk) 08:53, 3 September 2015 (UTC)

Citation 2 Doesn't exist anymore. — Preceding unsigned comment added by 24.55.1.148 (talk) 19:08, 21 September 2015 (UTC)

Distinguishing reference frames

The table in the article uses two different frames of reference for measuring acceleration:

• proper acceleration with respect to an Inertial frame of reference
• acceleration with respect to a Laboratory frame of reference

Before user:Cmglee's changes, the difference was hidden in the use of either g or G. Now we have the situation that the reader might compare, for example the Saab to the Bugatti and miss the reference that the Bugatti's acceleration is directed 40 deg from horizontal. This also affects the order of the table, for example the Saab accelerates faster than the Saturn V if one chooses the same frame of reference. What is good way of distinguishing the two that is easy to understand and not easily overlooked?--Debenben (talk) 17:56, 21 July 2016 (UTC)

Hi Debenben, That's a very good point, but it affects all the values, not just the g one. One remedy I can think of is to add asterisks and daggers for entries where the difference matters, and footnotes explaining them. I suppose there's a similar issue with gauge pressure and absolute pressure in Orders of magnitude (pressure), but at least it's scalar instead of vector addition. Cheers, cmɢʟee⎆τaʟκ 17:21, 24 July 2016 (UTC)

When the Bugatti achieves "0 to 100 km/h in 2.4 s, directed 40 degrees from horizontal", is it going uphill or downhill? It must make a difference, so why doesn't the article say? Maproom (talk) 08:45, 28 July 2016 (UTC)

@Maproom: It is not going uphill or downhill, it is going flat horizontal, just like the Saab. When the Saab is parked in the Garage, it accelerates with 0 g with respect to the Garage. When the Bugatti is parked in the Garage, its acceleration is 1 g with respect to an inertial frame - that's the difference. One should also note, that braking or changing direction is also an acceleration, which is not considered in both cases, which makes it different to the acceleration of the formula 1 car.--Debenben (talk) 11:46, 29 July 2016 (UTC)

If it's "going flat horizontal", why does the article say it's "directed 40 degrees from horizontal"? Maproom (talk) 14:55, 29 July 2016 (UTC)

@Maproom: Maybe the difference is best explained for the Saturn rocket: The engine produce a thrust of 1.14 g, which means the occupants always feel an acceleration of 1.14 g ( = acceleration with respect to an inertial frame = free falling reference frame e.g. a stone without any engines or ground support). If one takes a movie of launch, one would measure an acceleration of only 0.14 g with respect to the earth, because one has to subtract the earths gravity of 1 g. If one would launch the rocket upside down, one would measure an acceleration of 2.14 g with respect to the earth while the occupants still feel 1.14 g. If one launches the rocket horizontally without any additional forces by wheels, the occupants feel 1.14 g and the acceleration with respect to earth would be calculated by adding the two perpendicular vectors, so one gets sqrt(1^2+1.14^2) g with respect to earth. If the rocket gets wheels, additional forces act on it. Then the acceleration with respect to earth would be 1.14 g and the occupants feel sqrt(1^2+1.14^2) g directed arcsin(1/sqrt(1^2+1.14^2))=41.26 degrees from horizontal.--Debenben (talk) 16:33, 29 July 2016 (UTC)

@A.R., Maproom, and Cmglee: Since there no real input or new ideas from this RfC, let me list all options that I can think of

• (1) Split the article into something like Orders of magnitude (observed acceleration) Orders of magnitude (proper acceleration)
• (2) Split the list into two sections for the two reference frames
• (3) Split the list into two (three) sections, the first (two) for accelerations <10^2 g where the difference matters that distingish(es) reference frames
• (4) Make a <ref> annotation for each entry, that specifies the frame of reference
• (5) Use different colored rows for different reference frames, and explain the meaning of the color above (below) the table
• (6) Make an additional column that specifies the reference frame
• (7) Make two additional columns, such that g and m/s^2 are given with respect to both reference frames
• (8) Make the reader guess by not specifying it at all (status quo)

One can also combine the options, e.g. option 3+4+5+6: create two different tables for small and large values. The table for small values using different colors and an additional row with a custom ref-tag that specifies the frame of reference. From my point of view, the worst options are (1) and (8), I just included them for completeness.--Debenben (talk) 16:52, 7 August 2016 (UTC)

Option (6) seems the most convenient and least disruptive to the reading flow. Option (7) should be considered only if we can actually derive that information for every item in the table. A.R. (talk) 21:27, 7 August 2016 (UTC)

I'd say give the accelerations as lab reference and inertial reference frame in all cases up to where it makes no difference to the number. It's a simple calculation which doesn't fall foul of WP:OR, and doesn't complicate the table with footnotes, colours or explanations, and doesn't require us to create new articles. It also means that all the cases can be simply compared with each other. We can, if you like, also give the direction of the vector, like was done with the car acceleration case, where relevant. --Slashme (talk) 21:31, 7 August 2016 (UTC)

I'm fine with any sensible method which uses only 1 list and 1 section. Are we that confident that published sources make it unequivocal which reference each measurement is? cmɢʟee⎆τaʟκ 22:44, 7 August 2016 (UTC)

I doubt that they mention reference frames for things like the ultracentrifuge. From the mathematical point of view, the lab frame would make more sense, because the value would be independent of location, but the difference would be on the order of 0.0000016 g (on earth, for the usual orientation of the centrifuge), which is probably smaller than the measurement error. If the frame of reference is unclear for things like the formula 1 car, then the value is useless, like a number without units.--Debenben (talk) 12:50, 8 August 2016 (UTC)

All of the proposed fixes are kinda ugly. I'd rather not force the reader to try to figure out what's going on. I'd like to suggest an alternative. The issue only appears to relevant to a small number of items in the list, and the items in the list are generally arbitrary selections. Could we just changing a few items to avoid the problem entirely? I don't have alternatives to offer at the moment, but it would be a really nice fix. Alsee (talk) 02:38, 9 August 2016 (UTC)

@Alsee: One could also think of a option (1b) solution, only using proper acceleration. That is what it used to be like in 2011 [1] and that is where the strange way of measuring the Bugatti's acceleration comes from. But without any explanation, people will misunderstand the values and add values with a different frame of reference again and we are back at option (8).--Debenben (talk) 12:48, 9 August 2016 (UTC)

Whatever reference frame is used should be consistent across the whole article. Only exceptions should be labeled as using a different reference frame. Mooseandbruce1 (talk) 03:08, 10 August 2016 (UTC)

@Mooseandbruce1: What kind of labeling would you suggest? My interpretation of the article's history is the following: Part of the article used to be called Orders of magnitude (gravity) and some parts are taken from the article g-force. This means everything used to be proper acceleration. However from a physicists point of view, gravity refers to a phenomenon and not to a specific quantity like mass or gravitational/proper acceleration in a reference frame and the article moved to its current title. The term acceleration, unlike g-force, generally does not imply that it is measured in a specific reference frame. Yet this was still assumed to be the case. Then examples measured in a lab-frame were added using the wording "car acceleration" and "train acceleration" instead of just "acceleration of ..." to distinguish them. This unconventional distinction was easily overlooked, especially since values are given in units m/s^2 and g and g is linked to g-force which usually implies proper acceleration. User:KjellG therefore changed their units from G to g, which again is a distinction that is not commonly accepted or understood as such, hence the long-term result was option (8).--Debenben (talk) 19:40, 17 September 2016 (UTC)

Large Hadron Collider

The acceleration of a proton in the LHC is given in this page as 1.9x10^9 g. The formula given is (7 TeV/20min*c)/proton mass. Not sure where this comes from, but if it calculates from a zero initial velocity, then it's inaccurate. Beams go into the LHC already traveling near the speed of light (having been through other particle accelerators on the way), so they can't get much faster.

Beams enter the LHC with an energy of 450 GeV per proton. By the time they're finished accelerating, they're at 6500 GeV per proton (the energy that the collider currently operates at). Dividing energies by proton mass 0.938 GeV/c^2 gives a gamma factor of 479.7 at injection and 6,929.6 after acceleration. From equation y= 1/(sqrt(1-(v^2/c^2))), we get beam speeds of 299,791,806.5 m/s at injection and 299,792,454.9 after acceleration. The difference between these two numbers is 648.4 m/s. It takes 19 minutes to accelerate the beams all the way. From v=a*t, we find the acceleration to be only 0.55 m/s^2 (0.056 g).

Treating the LHC like a centrifuge, however, is how we get all the Gs. Centripetal force = (mv^2)/r. Force also = m*a. So m*a = (mv^2)/r. Since the beams are going so fast, we need to take relativity into account. So we multiply (mv^2)/r by the gamma factor, which is 6,929.6 at full energy. The beams are bent around a radius of 2,803 m. Working with m*a = (y*mv^2)/r, we get centripetal acceleration of 2.22x10^17 m/s^2 (2.27x10^16 g). This is much greater than the acceleration figure given on this page.

Savie Kumara (meow) 06:48, 13 August 2016 (UTC) Savie Kumara (meow) 06:48, 13 August 2016 (UTC)

Correction: the page states LHC proton acceleration as 1.9x10^8, not 1.9x10^9. Savie Kumara (meow) 07:02, 13 August 2016 (UTC)

This link gives many parameters of the LHC, including numbers I used (energy & gamma factor at injection and the collider's bending radius). https://edms.cern.ch/ui/file/445830/5/Vol_1_Chapter_2.pdf Savie Kumara (meow) 07:16, 13 August 2016 (UTC)

You are right. Just using the given formula "(7 TeV / (20 minutes * c))/proton mass" results in the value that was given. However I don't know what the formula is actually supposed to mean: Energy per beam/(proton mass*acceleration time*c) is not anything useful in my opinion. Additionally, the value is not really impressive: A (non-relativistic) proton in an electric field of 1 V/cm already accelerates with more than 10^11 m/s^2. That the mean acceleration is not really a characteristic value for an accelerator can be seen from the fact that for both your calculations, it does not really matter, whether the final speed is 0.99*c or 0.99999999*c, for the energy of a proton, it is a huge difference.--Debenben (talk) 20:34, 17 September 2016 (UTC)

Cars acceleration

The acceleration values in the table are average value, considering the ratio between the total change of speed (100 km/h) and the duration of the change. It would be more interesting to know the maximum acceleration: no car has a constant acceleration: the torque vs. rpm curve of the motor, the change of the gear rapport (if not an electric car) and the aerodynamical friction make the acceleration higher at the beginning and lower at the end. As I said, it would be more interesting to know the maximum acceleration: I suppose that the most of the other values are the peak value and not the average. --Angelo Mascaro (talk) 20:38, 26 January 2017 (UTC)

Jellyfish stinger

The cite for the acceleration of a jellyfish stinger does not provide details on the claim for the high acceleration. It mentions a response time and velocity, but not a travel time or distance for the stinger that achieves a modest speed of 18.6 m/sec. Equating the response time from the cite with the travel time of the stinger, the apparent constant-acceleration is (18.6 m/s) / (700 e-9 s) = (26,571,428 m/s^2) / (9.8 m/s^2) = 2,711,370-g , not 5.4e6 g. The cite doesn't say how a higher-than-constant acceleration of the stinger was determined -- if the response time and the travel time are the same. The Wikipedia article on jellyfish does not mention the acceleration of the stinger. - 71.166.96.134 (talk) 04:08, 18 June 2018 (UTC)

The abstract for ref 9 in the cite says "High-speed studies revealed the kinetics of discharge to be as short as 700 ns, generating an acceleration of 5,400,000 x g". What is being accelerated over what distance remains unclear to me. Uniform acceleration at 5.4e6 g for 700 ns will move something a distance of 0.5 * (9.8 * 5.4e6 m/s^2) * (700e-9 s)^2 = 1.3e-5 m = 13 microns. - 71.166.96.134 (talk) 12:29, 18 June 2018 (UTC)