If you were standing on a train travelling at high speed

[BrumJim]

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.

Not convinced that any molecules on the front of the train would be stationary, as the fly is a lot more elastic than the train. And has a lot less behind it. Actually, OK the very surface few layers would be, but only for a VERY short period of time. On a microscopic level, it is the fly that would take it all. Remember that the fly is essentially an elastic bag of water, hence at the moment of impact, whilst the very end of the head is going in one direction, the very end in the other direction, the velocity would vary along the length of its body. In reality, at some point this bag would explode, and each particle would act on its own, hence the splatter rather than a neat blob.

 

[marinyork]

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 think you better be careful with such definitions, that entitles quite a lot of people to be called engineers that wouldn't be dreamt of being called it .

Anyway quite a few people shorten things with analysis e.g. num anal.

 

[BrumJim]

I think you better be careful with such definitions, that entitles quite a lot of people to be called engineers that wouldn't be dreamt of being called it .

Anyway quite a few people shorten things with analysis e.g. num anal.

The Engineering Council call me an Engineer. I have a certificate on my wall to prove it. That's enough for me.

 

[Over The Hill]

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.

Vibration.

The balance wheel is held on a spindle between two points. It will have some movement in it.
The balance spring is a coil of fine wire also with movement in it.

Jog them around and it interrupts the smooth sweep of the balance making it take a little longer by it either going further or losing some of the momentum or power put in it by the mainspring. So repeating that over a ride many times will slow down the watch.

Think of a clock pendulum swinging and how it would slow if you knocked it a bit.

Next!

 

[Over The Hill]

Originally Posted by Over The Hill
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*

I actually am puzzled by this one and would like to know (assuming from your response that I am wrong) what would happen.

I cannot see how light would go any faster if emitted from a source travelling at the speed of light.

Similar to you not hearing bang from the gun before the bullet hits you.

 

[Norm]

I actually am puzzled by this one and would like to know (assuming from your response that I am wrong) what would happen.

I cannot see how light would go any faster if emitted from a source travelling at the speed of light.

For me, the question breaks down because of the assumption that the car can travel at the speed of light. What would have to happen to the car to get it to that speed, would it not have become, by necessity, light itself.

But then I never was very good at relativity. I'm still fascinated that light exhibits properties both of a wave and a particle.

 

[classic33]

Lost a wheel off your wagon?

The wheel flanges move backwards.

Think Finite element.

The flange on the wheel moves in the same direction as the wheel it forms part of.

Its the base of the wheel that is moving in the opposite direction to the train. Provided the track is stationary.

 

[marinyork]

This is something I've never thought about.

So if I stand with my back to the rotation of the earth, does the light from the torch I can see 300m away travel at the speed of light or the speed of light plus the speed of the earth's rotation?

I think my brain is about to start hurting...

Basically what you and OTH are talking about is called Galilean relativity with galilean transformations. Special relativity doesn't work like that. The frames that matter are you and the whatever else. Rather than everything being the same everywhere under Galilean transformations, under Lorentz transformations, distance and time warps and events may not even happen in the same order.

 

[Norm]

The flange on the wheel moves in the same direction as the wheel it forms part of.

Its the base of the wheel that is moving in the opposite direction to the train. Provided the track is stationary.

Someone needs to think a bit more laterally.

The flange does not always move in the same direction. When the bottom of the wheel is on the stationary track, the hub is moving forward so the bottom of the flange is moving backwards.

This is something I've never thought about.

So if I stand with my back to the rotation of the earth, does the light from the torch I can see 300m away travel at the speed of light or the speed of light plus the speed of the earth's rotation?

I think my brain is about to start hurting...

The speed of light is constant. Relatively.

 

[marinyork]

That's as maybe (whatever you're on about) but how fast is the light from the torch to my face travelling?

The speed of light. The fairly sedate pace of the earth's rotation in hundreds of miles an hour or the tens of thousands of miles and hour the earth is hurtling around the sun doesn't matter. All that matters is you and your torch.

 

[jimboalee]

When an object is travelling away from you at close to the speed of light, it displays the 'red shift'. This is why Father Christmas' sleigh is known to be a red colour.
When an object is travelling toward you at close to the speed of light, it displays the 'blue shift'.
This means Rudolf should be 'The Blue nosed' reindeer.

And why Brummies get their pressies first.

 

[marinyork]

Oh right, ta.

So what you're saying is that relatively, all other speeds are insignificant anyway because nothing gets anywhere near the speed of light?

It is not that the speeds are insignificant, it is just that light is weird compared to ordinary every day life.

Take a car on a strange motorway that has commited some traffic naughtiness. The galactic speed limit on the motorway is 70mph but the car can never quite reach that. Instead of the car being able to escape by doing 69.9mph and having the police catch them very slowly at a rate of 0.1mph much to their surprise the police come whizzing towards them at 70mph as if they are stood still. Even stranger if they they turn around and drive the wrong way down the motorway to try and trick the police and whizz past the closing speed isn't nearly 140mph but strangely still seems to be 70mph. Even stranger still someone having a tea of coffee at a motorway service station gazing out of the window can see someone in the car playing air guitar celebrating as they think they escape but they appear to be doing it in slow motion.

 

[Over The Hill]

Basically what you and OTH are talking about is called Galilean relativity with galilean transformations. Special relativity doesn't work like that. The frames that matter are you and the whatever else. Rather than everything being the same everywhere under Galilean transformations, under Lorentz transformations, distance and time warps and events may not even happen in the same order.

That's cleared it up then!

 

[marinyork]

Well I didn't claim to be much good at explaining things if you're interested there are some Stanford Lectures on relativity as part of the programme of getting their material out a bit more the last few years (Leonard Susskind is very famous)


View: http://www.youtube.com/watch?v=BAurgxtOdxY
probably best avoid the ones on general as they are a bit harder .

I recommend this simple book http://www.amazon.co.uk/Introducing...=sr_1_2?ie=UTF8&s=books&qid=1259230547&sr=8-2 it is 176 pages but mostly cartoons. They are available in quite a few public libraries.

 

[classic33]

When an object is travelling away from you at close to the speed of light, it displays the 'red shift'. This is why Father Christmas' sleigh is known to be a red colour.
When an object is travelling toward you at close to the speed of light, it displays the 'blue shift'.
This means Rudolf should be 'The Blue nosed' reindeer.

I thought Rudolphs red nose was red due to the speed(650 miles per second) at which she travels, along with all the other reindeer & the sleigh. Similar to the effect of an object entering earths atmosphere.

see
http://www.chainreactionbicycles.com/santaclaus.htm