Scrutable

"The rapid changes in G over the 4.6 seconds duration resulted in an altitude drop of 178ft (54m), from 37,362ft to 37,184ft," the report said.

Still, it beats all those reports misidentifying the controlled decent to 31,000 in three minutes as the turbulence event and not part of the emergency response.

shpalman wrote: Wed May 29, 2024 10:33 am "The rapid changes in G over the 4.6 seconds duration resulted in an altitude drop of 178ft (54m), from 37,362ft to 37,184ft," the report said.

Still, it beats all those reports misidentifying the controlled decent to 31,000 in three minutes as the turbulence event and not part of the emergency response.

Ha, you beat me; I saw that and was wondering whether I sh'd put it in the BBC Fails thread.

We have a classic case of a journalist rewording what someone said. What the BBC journalist said was unfortunate, but then their source was also rather unfortunate, though less unfortunate than how the BBC journo mangled. What the Singapore Transport Safety Investigation Bureau preliminary findings actually said was:

The Gravitational force (G), recorded as vertical accelerations, fluctuated between positive (+ve) 0.44G and +ve 1.57G for a period of about 19 sec.

As we can see, they define G not as the constant in Newton's Law, but as "Gravitational force". Einstein correctly makes clear that there is no such thing, but in the Newtonian framework, that rather more of us have learned to apply, it's a reasonable approximation. But we see that actually it was a pointless definition, as they use it with a different meaning when they come to use it. They indicate that what was actually measured by the instrumentation was vertical accelerations, which avoids these theoretical complications, and is much more sensible. And when they come to using G, we see that they actually mean what is more usually written as g, which they use as a unit to quantify the accelerations.

Rewritten as follows, it makes sense.

The Gravitational force (G), recorded as vertical accelerations, fluctuated between positive (+ve) 0.44Gg and +ve 1.57Gg for a period of about 19 sec.

The biggest error was using "G", rather than "g".

Hang on, so positive g means there's still a downward force? If so, and as it was positive all the time, why were people hitting the ceiling?

Brightonian wrote: Wed May 29, 2024 3:46 pm Hang on, so positive g means there's still a downward force? If so, and as it was positive all the time, why were people hitting the ceiling?

Because the force was applying on the aeroplane?

Gfamily wrote: Wed May 29, 2024 3:50 pm

Brightonian wrote: Wed May 29, 2024 3:46 pm Hang on, so positive g means there's still a downward force? If so, and as it was positive all the time, why were people hitting the ceiling?

Because the force was applying on the aeroplane?

Ah yes, so when it was greater than 1, and the passengers experiencing only 1g, then they'd be forced upwards?

Brightonian wrote: Wed May 29, 2024 3:46 pm Hang on, so positive g means there's still a downward force? If so, and as it was positive all the time, why were people hitting the ceiling?

I think you are right, but not being a proper physicist I just have to go through the motions to persuade myself. What accelerometers show is a bit surprising to people who, like me, have studied A-level Newtonian physics.

Standing stationary on the earth's surface, an accelerometer will show that you are accelerating upwards at g. I only recently learned this, and it's taking a bit of getting used to. As Newton correctly tells us, F=ma, so what's the force producing this acceleration? The answer is it is the reaction force from the ground. It seems a bit funny to think we are accelerating upwards and apparently not moving, but there's gravity for you.

Flying in an aircraft, in "level" flight, it is similar, the upwards acceleration being provided by the lift of the aircraft, which produces a similar effect on the passenger in their seat as the reaction force from the ground does sitting on a chair on the ground.

So if the vertical acceleration measured varied from +0.4g to +1.6g, the smaller number reflects reduced lift - the plane sinks - and the larger increased lift - the plane rises. So a sense of weightlessness would be when acceleration fell to zero, and people hit the ceiling with impact when it goes below zero. So I think I agree with you.

I can only suppose that perhaps for individuals, in their instantaneous particular motions within the aircraft at the time, and so experiencing specific impulses reflecting that, it wasn't uniformly so for them. They might be provided with some energy from an impulse, which, given their instantaneous situation and motion, was enough to hit the ceiling. Was it the case that everyone who wasn't secured in place hit the ceiling?

I think it's fine to use Newtonian physics with the added gravitational "force" from the Earth. Then you can also decide whether to consider things from the frame of the aircraft which was decidedly non-inertial for those critical moments.

To hit the ceiling would either require the plane accelerate downwards faster than you'd freefall, or that there's an acceleration upwards followed by an acceleration downwards such that your initial velocity when you start freefalling is "up" relative to what the plane is doing.

Or to just read the rest of the report for f.ck's sake.

Never mind.

IvanV wrote: Wed May 29, 2024 1:32 pmWe have a classic case of a journalist rewording what someone said. What the BBC journalist said was unfortunate, but then their source was also rather unfortunate, though less unfortunate than how the BBC journo mangled. What the Singapore Transport Safety Investigation Bureau preliminary findings actually said was:

The Gravitational force (G), recorded as vertical accelerations, fluctuated between positive (+ve) 0.44G and +ve 1.57G for a period of about 19 sec.

But I note that it said, after that, "This would have caused the flight to begin to experience slight vibration", because if you'd read further instead of trying to solve it with general relativity, you'd realize that this wasn't the main event:

d. At 07:49:40 hr, the aircraft experienced a rapid change in G as recorded vertical acceleration decreased from +ve 1.35G to negative (-ve) 1.5G, within 0.6 sec. This likely resulted in the occupants who were not belted up to become airborne.

e. At 07:49:41 hr, the vertical acceleration changed from -ve 1.5G to +ve 1.5G within 4 sec. This likely resulted in the occupants who were airborne to fall back down.

f. The rapid changes in G over the 4.6 sec duration resulted in an altitude drop of 178 ft, from 37,362 ft to 37,184 ft. This sequence of events likely caused the injuries to the crew and passengers.

Writing this last point with g instead of G doesn't fix it.

Never mind this either.