If you were standing on a train travelling at high speed

[Tollers]

Tollers.

Please explain to everyone why my mention of the Earth's rotation (Coriolis Effect) and mass having gravity is 'Crap'.

Calm down dear. I wansn't commenting on the jumping on a train puzzle, more the flysplatting in infantecimal micro-movements

Tollers

 

[cisamcgu]

I think it does not work in the same way as other moving objects as light cannot move faster even if the source of the light is moving. The car moving at the speed of light cannot throw a light ahead of itself.

*sighs*

 

[jimboalee]

Assuming that to be true the reason may be -

The timekeeping is down to the movement of the balance spring which is wound around a balance wheel. If the balance wheel runs better it will run further on each stroke so with each stroke being longer the watch runs slower.

Now tell me why the thing slows down even more when I'm riding my bike, and then comes back to accurate timekeeping when I'm sitting at my desk.

 

[BrumJim]

Spent a whole night once bouncing up and down trains.

Unfortunately I cannot add to this thread as:
a) The trains were stationary at the time,
I was more interested in the condition of the floorboards than the physics of where I would land if I jumped straight upwards.
c) As a professional engineer working for a small firm, we can answer that one for you in a signed-off report suitable for submitting to your customer, but we need an order number before we can start work.

 

[jimboalee]

Calm down dear. I wansn't commenting on the jumping on a train puzzle, more the flysplatting in infantecimal micro-movements

Tollers

Infinitesimal micromovements.

Everything we observe is moving. This is the established norm.

We know objects move because the photons that have reflected off the object appear to be coming from a different position during our observation.
The 'update rate' of our brain must be the smallest micromovement.

 

[BrumJim]

Infinitesimal micromovements.

Everything we observe is moving. This is the established norm.

We know objects move because the photons that have reflected off the object appear to be coming from a different position during our observation.
The 'update rate' of our brain must be the smallest micromovement.

You are getting a bit existential here. Whilst you observe micro-movements, Newton will tell us that an object continues at the same speed and in the same direction, unless acted on by an external force, hence doesn't progress in small jumps.

 

[BrumJim]

Now for the interesting observation that a fly can stop a speeding train.

Lets say a fly and a train are heading towards each other in opposite directions and just before the impact the fly is travelling north while the train is travelling south. Obviously just after the impact the fly and the train are both travelling in the same direction south. During the impact the fly rapidly decelerates and then starts accelerating in the opposite direction which means that for a tiny fraction of a second the fly must be stationary. At the point in time when the fly is stationary the fly is also in contact with the train, which means that the train must also be stationary.

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My answer is NO, because:

At the instant that the fly hits the train (assume the windscreen, just for visual effect), its average speed is zero. However its head, which is in contact with the windscreen, is now travelling at the same speed as the train, whilst its arse is travelling at its original speed. Somewhere near the arse, the body is not moving at all, but this bit isn't in contact with the train. Yet.
The end result of this is that the head gets pushed through the backside, and we end up with a yellow sticky mess on the windscreen.
X 50, and the driver uses his wipers and washer fluid, and wipes the mess of the windscreen.

 

[jimboalee]

I doubt whether a high speed close up video has been taken of a fly hitting a train's windshield.

I know the combustion of gases in a motor car's engine has. It was done to evaluate the burn pattern and flame-front of the explosion. We all knew the piston was accelerating, but for the purposes of developing the cylinder head shape, the whole movement was split into very small sections.
10 minutes of a degree crank angle, as I recall.
Each image showed the conditions at that instant. Cyl head and piston crown were altered to improve the cylinder pressure at certain points in the piston's travel, certain crank angles.

When someone films a fly hitting a train, the positions of the fly and train will be quantified vs a trackside datum.
At the precise moment of impact, the image will show a fly in the process of being crushed by its own arse and a train. Both will appear to be at a standstill.

It may be seen the train's progress is slower after impact.
The fly's speed will increase greatly.

 

[BrumJim]

Mass of train = 466 tonnes, empty (Class 390)
Mass of fly = 5 grammes?
Momentum of train at 160 km/h = 20711111.0904kgm/s
Momentum of fly at = 2m/s (just less than 5 mph - fly isn't that worried) = 0.01kgm/s

Therefore combined momentum after impact = 20711111.0804kgm/s

A scientist would say that the fly slows the train down. An engineer would say that it doesn't.

 

[jimboalee]

Is that a 'keen & green' engineer, or a 'hairy arsed' engineer?

 

[BrumJim]

Bloke who doesn't know one end of a spanner from the other, but understands the influence of the modelling of boundary conditions on the effectiveness of an FEA model.

 

[jimboalee]

Bloke who doesn't know one end of a spanner from the other, but understands the influence of the modelling of boundary conditions on the effectiveness of an FEA model.

I was going to mention Finite Element Analysis, but it has the letters A,N,A& L in it.

BTW, one end is a 'ring' and the other an 'Open Ended'. That variety is called a 'combination' spanner.

 

[jimboalee]

What do you say to the statement "An engine is a mechanism which produces motion from energy".

If a person has never designed or developed such a machine, they cannot entitle themselves as "Engineer".

 

[JtB]

My answer is NO, because:

At the instant that the fly hits the train (assume the windscreen, just for visual effect), its average speed is zero. However its head, which is in contact with the windscreen, is now travelling at the same speed as the train, whilst its arse is travelling at its original speed. Somewhere near the arse, the body is not moving at all, but this bit isn't in contact with the train. Yet.
The end result of this is that the head gets pushed through the backside, and we end up with a yellow sticky mess on the windscreen.
X 50, and the driver uses his wipers and washer fluid, and wipes the mess of the windscreen.

I tend not to favour the 'fly turning inside out' based answers because they tend to avoid the issue. Irrespective of what the fly's arse is doing, the fly's head still needs to change direction while in contact with the train and so that doesn't really explain why the train itself doesn't need to stop.

Personally, I prefer the 'elasticity based' answers (note: elasticity is the physical property of a material that returns to its original shape after an external force that made it deform, is removed) which recognise that some molecules on the surface of the train may well be stationary at some point during the impact, but that's about it. In reality though, since the train is not travelling in a vacuum them the slipstream around the train is probably going to absorb much of the impact anyway.

 

[BrumJim]

Leaves Civils up S**t Creek.

Which needs a bridge across it, to be honest. And some suitable road infrastructure to service it. And divert the water flow a bit whilst you are at it.

Anyone can design an engine. Good engineers don't bother, as someone has already built a better one more cheaply than they could. Great engineers can give it a go, though.

My favourite story about Frank Whittle was that when they fired up the very first UK jet engine on the test bed, and it worked, everyone cheered, except Frank. Why not? "Of course it worked - that's what I designed it to do." Was his response. Good engineering is not about getting something to work, it is knowing why it worked in the first place.