If you spin a propellor...

touch · 27 Feb 2010 at 02:21

WalesOwl said:
Right, wiki doesn't seem to know a lot more about it either. Pretty interesting that we apparently see continuously.

Does the brain continuously process the information as well?

It's not really that simple.
AFAIK, your brain "updates" different things at different speeds. Things around the edges of your field of vision are seen differently from things you are focused on. Movement is all you really need to notice in these areas, no detail is needed. I dont think you even see colour in these areas, but your brain will cleverly colour things in for you based on what you see in the coloured area of vision (middle bit that you are focused on).

Your brain also fills in a lot of what you think you are seeing. For example, when moving your vision around quickly. If you pan very quickly with a video camera you just get a blur. Your brain stops this happening by freezing your vision for a short while until you're focused again. (You might sometimes notice this if you look at a clock at exactly the right time, it sometimes looks like the first second is longer than next ones)

(this is what i remember from school many years ago, and it may all be wrong

)

Raymond Lin · 27 Feb 2010 at 02:26

Is this another Sandwiches/treadmill thread?

Nate--IRL-- · 27 Feb 2010 at 02:26

blah blah blah blah

The answer is still

c) Who cares.

Nate

bigjimmyauk · 27 Feb 2010 at 02:32

touch said:
It's not really that simple.
AFAIK, your brain "updates" different things at different speeds. Things around the edges of your field of vision are seen differently from things you are focused on. Movement is all you really need to notice in these areas, no detail is needed. I dont think you even see colour in these areas, but your brain will cleverly colour things in for you based on what you see in the coloured area of vision (middle bit that you are focused on).

Your brain also fills in a lot of what you think you are seeing. For example, when moving your vision around quickly. If you pan very quickly with a video camera you just get a blur. Your brain stops this happening by freezing your vision for a short while until you're focused again. (You might sometimes notice this if you look at a clock at exactly the right time, it sometimes looks like the first second is longer than next ones)

(this is what i remember from school many years ago, and it may all be wrong )

*highlighted text* i know what you mean it's almost like that second has gone back it's very rare to see it tho but remember it happening a few times in the past.

Danm54 · 27 Feb 2010 at 02:34

bigjimmyauk said:
*highlighted text* i know what you mean it's almost like that second has gone back it's very rare to see it tho but remember it happening a few times in the past.

Ive done that a few times, can never do it again though!

bigjimmyauk · 27 Feb 2010 at 02:40

Danm54 said:
Ive done that a few times, can never do it again though!

lolz i just tried it with the windows 7 clock and u can do it pretty frequent if u time it right watch 10 seconds go buy clicking somethings everytime a second passes look away and continue the clicking rythem for another 5-10 seconds then look back at the clock... it's working for me about 2-3 times outta 5

you gotta remember tho the brain works slower when tired. which brings on a off topic question

example if u played crysis at 15frames per second when wide awake then played it again when almost falling asleep after being up for many many hours to that point where concentration is very hard would the game appear to run smoother or more choppy............... i don't think it would look the same as when i'm tired it takes me considerably longer to focus on the text on my monitor than it does in the peak of day when wide awake.

V4NT0M · 27 Feb 2010 at 03:22

Where is this propeller, on earth? I would gather that if it were one earth the propeller would turn into a massive Catherine wheel and burn up from all the friction.

Bennie-Mac · 27 Feb 2010 at 05:52

bigjimmyauk said:
Erm the whole thing would spin the same speed!! the edges of a circle do not spin faster than the centre if that was the case cd's wouldn't work

bigjimmyauk said:
okget a cd draw a line through it in the centre and then spin it using a reference point both lines would cross the same point at the same time if they didn't the lines would move

Do you know how these work?

trent · 27 Feb 2010 at 05:59

Consider a point on the outer circumfrance of the disk.

Draw a tangent to that point on the curve and draw a line @ 90 degrees to the tangent to the inner circumfrance of the disc.

This gives a line which is always the same, the 2 points are always in the same position relative to one another - this is true even as the disc is turning.

So as the disc rotates 90 degrees round the two points do too. However relative to each other they have not moved.

So the outer circum point has moved pi * d.1 * 90/360
d.1 = diameter to of entire disk

And the inner circum point has moved pi * d.2 * 90/360
d.2 = diameter of 'hole at centre of disk'

It is clear that d.1 > d.2 and so the point on the outer circumfrance will have travelled further in the same time.

As avg. speed = distance / time

And d.1 distance > d.2 distance, speed.1 will be greater than speed.2.

Thus the outside of the disc has a greater average speed.

neodude · 27 Feb 2010 at 07:40

bigjimmyauk said:
Erm the whole thing would spin the same speed!! the edges of a circle do not spin faster than the centre if that was the case cd's wouldn't work

lol, thats brilliant. We need that made into a demote.

arknor · 27 Feb 2010 at 08:09

Aedus said:
You'd see nothing, if you took a picture of it though you'd see a black circle I guess.

EYES CAN NOT SEE AT THE SPEED OF LIGHT!

I WIN THIS THREAD (unless someone else realised first)

human eye can/brain can only see a few hundred fps btw estimated to be between 200-300 (obviously you wouldnt be able to make out 200 different frames)

you would probably see a grey flicker (assuming the fan blades are grey)

Cosimo · 27 Feb 2010 at 09:23

arknor said:
I WIN THIS THREAD (unless someone else realised first)

You can’t win this thread it’s not a competition.

arknor · 27 Feb 2010 at 09:29

simulatorman said:
You can’t win this thread it’s not a competition.

lies lies and tiny eyes i demand you give up the prize!

Mirage · 27 Feb 2010 at 09:40

If you put a CD on a treadmill do you get to play space invaders whilst it loads?

Inquisitor · 27 Feb 2010 at 09:47

I suppose you'd just see a blur that occludes whatever's behind the propeller to an extent depending on the ratio of blade area to non-blade area around the circumference over different radii. Certainly nothing particularly unintuitive.

Also, it doesn't make sense to say something is rotating at the speed of light; you need to specify angular velocity/frequency, since the tangential speed depends on the radius, so different parts of the propeller will be moving at different speeds.

Hamzter · 27 Feb 2010 at 09:49

I suspect the blades would very quickly detach from each other, and bury themselves several km underground/launch into space. Therefore, you wouldn't be able to see the blades.

If the blades were made by unobtanium, the attached vehicle would very quickly take off and disappear over the horizon. Therefore, you wouldnt be able to see the blades.

If the vehicle was securely anchored, the blades would very quickly heat to 10,000s of degrees, the white hot heat would burn your retinas out. Therefore, you wouldn't be able to see the blades.

If you put the vehicle in a vacuum (or wore some nifty sunglasses), you'd see a very blurred propellor, with an opacity equivalent to the % area it covers. So if the propellor covered 20% of the area in the circle from your viewpoint, you would see a circle with roughly 20% opacity. Then you'd asphyxiate from being stood in a vacuum, therefore you wouldn't be able to see the blades.

Hamzter · 27 Feb 2010 at 09:54

Oh, and if you were looking it from an angle, the tips of the props would turn blue/red from doppler shifting!

dandos23 · 27 Feb 2010 at 10:20

Hamzter said:
I suspect the blades would very quickly detach from each other, and bury themselves several km underground/launch into space. Therefore, you wouldn't be able to see the blades.

If the blades were made by unobtanium, the attached vehicle would very quickly take off and disappear over the horizon. Therefore, you wouldnt be able to see the blades.

If the vehicle was securely anchored, the blades would very quickly heat to 10,000s of degrees, the white hot heat would burn your retinas out. Therefore, you wouldn't be able to see the blades.

If you put the vehicle in a vacuum (or wore some nifty sunglasses), you'd see a very blurred propellor, with an opacity equivalent to the % area it covers. So if the propellor covered 20% of the area in the circle from your viewpoint, you would see a circle with roughly 20% opacity. Then you'd asphyxiate from being stood in a vacuum, therefore you wouldn't be able to see the blades.

This is just outstanding. ROFLMAO

touch · 27 Feb 2010 at 10:31

Hamzter said:
If the blades were made by unobtanium, the attached vehicle would very quickly take off and disappear over the horizon. Therefore, you wouldnt be able to see the blades.

This was mentioned earlier in the thread. I suspect that a prop turning at the speed of light (assuming it's possible) would produce very little thrust.

dandos23 · 27 Feb 2010 at 10:37

touch said:
This was mentioned earlier in the thread. I suspect that a prop turning at the speed of light (assuming it's possible) would produce very little thrust.

The thrust would depend on the "angle of attack"

If you used the prop from a "Spitfire" then you would end up with no thrust because the angles are all wrong for that speed.

If you built a prop for this experiment, then you would give it the correct "angle of attack" to produce the amount of thrust that you require.