Mathematical equations, physics buffs.

[EgoFG]

Originally Posted by flappist

Well the headlights are also travelling at the speed of light so relative to the starship they just work normally but relative to you depending on your reference point they may appear to do many different things. They won't ACTUALLY do different things just look like they are.

It is all about reference.

You are on the side of the road.
A car drives past at 100km/h with the horn blowing.
The frequency of the horn changes as it goes past but the driver does not hear any difference.

Did the horn change or not change?

I am getting old .. but ...

The speed of light is relative to the observer. So if a vehicle is progressing at a good speed , the light from the headlights is traveling at the speed of light relative to the observer inside the vehicle, as well as relative to the observer on the side of the road.

That having been said the "wave property of light" proponents will mention "dopler shift" in light coming from distant galaxies (this it the crazy horn thingy - prolly got a diff name for light - it is when the waves compress to give a higher frequency).

but ordinary rules of physics do not really apply when an object (other than light) approaches the speed of light - IIRC, this is because the mass of the object approaches infinite, as the speed of an object approaches the speed of light - making empirical testing impossible.

[hawke]

If we accept that a planes lift is a function of its wing contour, more area on one side, causing a pressure differential and lift, what happens when a plane flys upside down?

As the wings dont change shape, wont the aero force combine with the gravitational force and send it crashing down? We know this doesnt happen, so what goes on, or have I missed the bus entirley?

[buggo]

Originally Posted by flappist

You have the wrong idea.

Aircraft do not accellerate due to power being applies to the wheels, the accellerate because they push against the air.

Once the air flows fast enough to create a pressure differential between the top and bottom of the wing greater than the mass of the aircraft it will move upwards.

If the air is moving slower relative to the ground than the plane it will move up and forward, if the same it will just move up and if greater it will move up and backwards BUT IT WILL ALWAYS TAKE OFF

I know they aren't driven by their wheels, I'm not that delayed. They use engines to generate thrust, which makes them move foward.
If the plane is on a treadmill, they do not need to be on, because the treadmill is spining the wheels at the same speed the engines would.

If the plane is on a treadmill, the air is moving no faster nor slower than it was before the plane was on the treadmill. If it did not take off before getting on, what are spinning wheels going to do?

And yeah I know how an areofoil works, in theory, I did a whole term just on that shape.

Please tell me we are talking about complete different scenarios
Like the treadmill moves or something.

[buggo]

Originally Posted by hawke

If we accept that a planes lift is a function of its wing contour, more area on one side, causing a pressure differential and lift, what happens when a plane flys upside down?

As the wings dont change shape, wont the aero force combine with the gravitational force and send it crashing down? We know this doesnt happen, so what goes on, or have I missed the bus entirley?

Angle of attack and thrust.

[shedcoupe]

Originally Posted by buggo_gt

Angle of attack and thrust.

I say that wings 'blow' ie. that they push air down so that the plane is pushed up, and that the airfoil cross-section is there merely to reduce drag.
Others say that wings 'suck' ('lift').
Rubbish. If that were true, a stunt plane could not fly upside down without being 'sucked' onto the ground.

Incidentally, wings' leading edges are usually pitched 'up' a bit relative to the fuselage centreline - if wings were parallel they would 'suck' more if they did actually 'suck'.

[shedcoupe]

Originally Posted by LXL15

You're not alone, I love this stuff. I just have nothing to say except I love New Scientist. Nerdy? Yes, very loud and proud...

'New Scientist' is okay, but I prefer 'Nerd Scientist' magazine.
The centrefolds of calculation sheets are way hotter.

[flappist]

Originally Posted by SteveJH

If the runway was long enough could he have just landed with the wind in that case rather then against it?

Apart from being illegal and way outside the design parameters of the aircraft he would have been doing over 160km/h in a vehicle with 3 tiny wheels and almost no brakes.

It would have been SPECTACULAR....

[LXL15]

Originally Posted by shedcoupe

I say that wings 'blow' ie. that they push air down so that the plane is pushed up, and that the airfoil cross-section is there merely to reduce drag.
Others say that wings 'suck' ('lift').
Rubbish. If that were true, a stunt plane could not fly upside down without being 'sucked' onto the ground.

Incidentally, wings' leading edges are usually pitched 'up' a bit relative to the fuselage centreline - if wings were parallel they would 'suck' more if they did actually 'suck'.

Planes definitely suck...air. think about the deflection that is caused by the wings, its nowhere near 90 degrees. Then think of the amount of air required to be displaced in order to lift a fully loaded airliner, then think of the power and effort required to lift a harrier jump jet vertically even when its using a purpose designed 'blow' system. We did the calculations once in an aerospace class, the effect is so negligible that you only really look at the pressure differential for lift.

As mentioned above, lift can still be generated when upside down thanks to thrust and angle of attack, just like it can be lost by a too low angle of attack when flying the right way up.

[shedcoupe]

Originally Posted by LXL15

Planes definitely suck...air. think about the deflection that is caused by the wings, its nowhere near 90 degrees. Then think of the amount of air required to be displaced in order to lift a fully loaded airliner, then think of the power and effort required to lift a harrier jump jet vertically even when its using a purpose designed 'blow' system. We did the calculations once in an aerospace class, the effect is so negligible that you only really look at the pressure differential for lift.

As mentioned above, lift can still be generated when upside down thanks to thrust and angle of attack, just like it can be lost by a too low angle of attack when flying the right way up.

Thanks for that - I'll have to ponder the physics for a while ......

I have in fact been known to be wrong on one or two thousand occasions.

[b055m4n]

i got a headache.......

[flappist]

Originally Posted by buggo_gt

I know they aren't driven by their wheels, I'm not that delayed. They use engines to generate thrust, which makes them move foward.
If the plane is on a treadmill, they do not need to be on, because the treadmill is spining the wheels at the same speed the engines would.

If the plane is on a treadmill, the air is moving no faster nor slower than it was before the plane was on the treadmill. If it did not take off before getting on, what are spinning wheels going to do?

And yeah I know how an areofoil works, in theory, I did a whole term just on that shape.

Please tell me we are talking about complete different scenarios
Like the treadmill moves or something.

You all get this fixation that the "treadmill" will stop the forward motion of the aircraft.

It does not as all it does is spin the wheels, the plane moves relative to the air, the only reason it has wheels is to reduce friction with the ground.
Floaty, ski and SSH aircraft doen't even need wheels.

Assuming no bearing friction and indestructable treadmill and wheels the treadmill and wheels will spin at an infinite rate but the aircraft will still move forward as it pushes against the air not the ground....

If the treadmill and wheels obey the normal laws of physics it will be up to whether the treadmill or wheels fail first.

Grab a pushbike and hold it on a moving walkway. From outside the walkway grab the frame and start rolling it forward. If the walkway speeds up what happens?

The pushbike wheels spin faster, that is all.......

[flappist]

Originally Posted by LXL15

Planes definitely suck...air. think about the deflection that is caused by the wings, its nowhere near 90 degrees. Then think of the amount of air required to be displaced in order to lift a fully loaded airliner, then think of the power and effort required to lift a harrier jump jet vertically even when its using a purpose designed 'blow' system. We did the calculations once in an aerospace class, the effect is so negligible that you only really look at the pressure differential for lift.

As mentioned above, lift can still be generated when upside down thanks to thrust and angle of attack, just like it can be lost by a too low angle of attack when flying the right way up.

There are 5 forces that control aviating; thrust, drag, lift, weight and casa.....

[13101093]

and orange is actually blue on the inside before you cut it open...

[RepSpec]

Originally Posted by b055m4n

i got a headache.......

glad im not the only one...

btw...wheres Sheldon and Leonard when u need them...

[shedcoupe]

Originally Posted by RepSpec

glad im not the only one...

btw...wheres Sheldon and Leonard when u need them...

Wolowitz and Koothrappali not good enough for ya than ???

[buggo]

Originally Posted by flappist

You all get this fixation that the "treadmill" will stop the forward motion of the aircraft.

It does not as all it does is spin the wheels, the plane moves relative to the air, the only reason it has wheels is to reduce friction with the ground.
Floaty, ski and SSH aircraft doen't even need wheels.

Assuming no bearing friction and indestructable treadmill and wheels the treadmill and wheels will spin at an infinite rate but the aircraft will still move forward as it pushes against the air not the ground....

If the treadmill and wheels obey the normal laws of physics it will be up to whether the treadmill or wheels fail first.

Grab a pushbike and hold it on a moving walkway. From outside the walkway grab the frame and start rolling it forward. If the walkway speeds up what happens?

The pushbike wheels spin faster, that is all.......

I must be using different treadmills, the ones I use do not move 1mm foward, backward or sideward. Yet I run Km's without getting anywhere???
Or do you mean it's on a conveyor belt that moves in the same direction at the same speed as the plane? So wheels aren't moving, yet the plane itself is, in that case yeah of course it will fly.

[Iggypoppin']

When I did the experiment I used a VTOL jet.

[LukeyST]

About aerofoils 'not sucking', firstly 'sucking' is absolutely rubbish terminology lol, secondly an aerofoil achieves lift by being pushed from the underside by the pressure differential from top to bottom. Greater pressure forces wing up to try and equalize pressure, not lower pressure 'sucking'.

Lift (N) = pressure differential (N/m^2) x aerofoil area (m^2)

Where pressure differential = pressure on lower surface - pressure on upper surface

About the relativity thing, say a car was travelling towards you at 1000m/s (unrealistic i know) with its headlights on, the light will still only travel at the speed of light (c = 3x10^8 m/s) towards you in your reference frame NOT at c+1000m/s which many people seem to think. The speed of light is CONSTANT, what changes is the perception of time ie. the driver will not have the same perception of the length of a second as the person standing on the side of the road. I know its quite a big mind-******* but you can get your head around the concept eventually.

SPEED OF LIGHT is CONSTANT no matter what reference frame you are in.

TIME is what CHANGES, or rather the perception of time.

Which begs the question, what is time?

Originally Posted by shedcoupe

Wolowitz and Koothrappali not good enough for ya than ???

They always seem to get left out of things in the show, Howard because he is an engineer (not a doctor like the rest) and Raj seemingly for racist-humour reasons?

[Iggypoppin']

Originally Posted by LukeyST

About aerofoils 'not sucking', firstly 'sucking' is absolutely rubbish terminology lol, secondly an aerofoil achieves lift by being pushed from the underside by the pressure differential from top to bottom. Greater pressure forces wing up to try and equalize pressure, not lower pressure 'sucking'.

Lift (N) = pressure differential (N/m^2) x aerofoil area (m^2)

Where pressure differential = pressure on lower surface - pressure on upper surface

About the relativity thing, say a car was travelling towards you at 1000m/s (unrealistic i know) with its headlights on, the light will still only travel at the speed of light (c = 3x10^8 m/s) towards you in your reference frame NOT at c+1000m/s which many people seem to think. The speed of light is CONSTANT, what changes is the perception of time ie. the driver will not have the same perception of the length of a second as the person standing on the side of the road. I know its quite a big mind-******* but you can get your head around the concept eventually.

SPEED OF LIGHT is CONSTANT no matter what reference frame you are in.

TIME is what CHANGES, or rather the perception of time.

Which begs the question, what is time?



They always seem to get left out of things in the show, Howard because he is an engineer (not a doctor like the rest) and Raj seemingly for racist-humour reasons?

Time is a measuring device used to sequence events.
Distance over speed. I stole that from wiki.

[gtfpv]

HERES A QUESTION FOR THE SPEED OF SOUND . . when a plane is traveling at 2 times the speed of sound , is the sound always falling further behind the plane ?
eg the plane broke the speed of sound and is travelling at mach 2 . 10 seconds ago , so the sound is 20 seconds behind the plane , in 1 minute the sound is now 2 minutes behind the plane , and after 1 hour the sound is now 2hours behind the plane ? SOMEONE EXPLAIN THIS TO ME .

[LukeyST]

Originally Posted by Iggypoppin'

Time is a measuring device used to sequence events.
Distance over speed. I stole that from wiki.

You can't define something by using something that involves what your trying to define ie. speed is distance per time unit.

I asked the question from more of a philosophical perspective. What is time? Some say its just the fourth dimension (x,y,z,t) where matter lies in 'x,y,z' and events occur as it moves along 't'. Thoughts?

[flappist]

Originally Posted by buggo_gt

I must be using different treadmills, the ones I use do not move 1mm foward, backward or sideward. Yet I run Km's without getting anywhere???
Or do you mean it's on a conveyor belt that moves in the same direction at the same speed as the plane? So wheels aren't moving, yet the plane itself is, in that case yeah of course it will fly.

On your treadmill you are trying to move forward by pushing against the track of the treadmill.
The aircraft is pushing against the air above the treadmill.

If you were standing on your treadmill holding a rope that was being pulled forward then you would move forward regardless of what the treadmill did because your motion is not being provided by your feet.

[flappist]

Originally Posted by gtfpv

HERES A QUESTION FOR THE SPEED OF SOUND . . when a plane is traveling at 2 times the speed of sound , is the sound always falling further behind the plane ?
eg the plane broke the speed of sound and is travelling at mach 2 . 10 seconds ago , so the sound is 20 seconds behind the plane , in 1 minute the sound is now 2 minutes behind the plane , and after 1 hour the sound is now 2hours behind the plane ? SOMEONE EXPLAIN THIS TO ME .

The sound comes from the point where the aircraft is at the time the sound is made so it is always coming from the aircraft.

All that happens is that if the aircraft is travelling towards you it will get to you before you hear it coming.

If it were travelling at the speed of light it would get to you before you could see it coming.

It only appears to come from behind because in the time it takes for the sound to get to you the aircraft has move from the point where the sound was made. This is not just a phenomon of supersonic travel.

Watch a V8 supercar race in real life standing back a few hundred metres from the track. Close your eyes. Listen for the cars and then open your eyes to look at them. They will not be where you are looking rather they will be further down the track.

In your original question the sound would only appear "2 hours" the behind the aircraft if you were observing it from a point that is "1 hour" from where the aircraft was when it made the sound.

[Airmon]

Originally Posted by shedcoupe

Well, assuming that G = 9.8 m/s² and pi = 3.142, and T = obviously it must be zero, then the answer is : x = 'with a chicken'.

Bad assumption. 'G' is traditionally Newtons Gravitational constant (among other things but in this context) not 'g' which is gravity in your frame of reference. Which would be 9.81 but would depend on your altitude above sea level and then you can use G to calculate g
Been so long I cant remember G, its quite large from memory.

Originally Posted by Work Horse

Oldie but a goodie

a = 1, b = 1

a = b
a^2 = b^2
a^2 - b^2 = 0
(a-b)(a+b) = 0
(a-b)(a+b)/(a-b) = 0/(a-b)
1(a+b) = 0
(a+b) = 0
1 + 1 = 0
2 = 0
1 = 0
1 + 1 = 1

You can't divide zero or divide anything by zero. You would need to simplyfy out (a-b)(a+b) and add or subtract anything to the other side.
Hence the assumption 1=0 etc is false.

As for the Airplane taking off, I dont know enough about Aerofoils to hazzard an accurate conclusion and am not involved in Aeronautics.
However I would think that if you could take off in a plane on the spot someone would be using it? Would be helpful for say Aircraft carriers. This is however not going to work as planes like that use Jets and thrust to gain air speed to gain lift.
The debate would be more whether a propellor passes a large enough volume of air at a large enough speed to gain lift. I wouldnt expect a Jet-turbine to do that, but again, don't know enough on the subject to say for sure, can only speculate.



And sound is not relative like light.


Here's one for you, is Light a particle or a wave????? No fence sitting!

[LukeyST]

Originally Posted by Airmon

As for the Airplane taking off, I dont know enough about Aerofoils to hazzard an accurate conclusion and am not involved in Aeronautics.
However I would think that if you could take off in a plane on the spot someone would be using it? Would be helpful for say Aircraft carriers. This is however not going to work as planes like that use Jets and thrust to gain air speed to gain lift.
The debate would be more whether a propellor passes a large enough volume of air at a large enough speed to gain lift. I wouldnt expect a Jet-turbine to do that, but again, don't know enough on the subject to say for sure, can only speculate.

Here's one for you, is Light a particle or a wave????? No fence sitting!

Lift only comes from relative air speed. Thats why planes take of into the wind, 'free speed' basically. And im pretty sure they use this technique on aircraft carriers also? Both using windspeed and ship speed. So if there is a wind of say 50km/hr and the ship is capable of 25km/hr they put they ship into the wind and have a 75km/hr windspeed advantage, if you need 300km/hr airspeed to take off that means you would then only need to be going 225km/hr (relative to the ship deck) to take off.

If they dont use this method they should lol, but im confident they do.

On the light particle thing, isnt light supposedly photon's? which is a mass-less particle. The theory of it being mass-less falls apart though when u consider gravity can bend light, and to be effected by gravity you need a mass......

Im going with its a particle (photons), but unsure about the whole 'mass-less' thing.

[Rodp]

Originally Posted by buggo_gt

I must be using different treadmills, the ones I use do not move 1mm foward, backward or sideward. Yet I run Km's without getting anywhere???
Or do you mean it's on a conveyor belt that moves in the same direction at the same speed as the plane? So wheels aren't moving, yet the plane itself is, in that case yeah of course it will fly.

http://www.youtube.com/watch?v=YORCk1BN7QY

You legs are providing your forward momentum.

Lets say you're on a treadmill matching the treadmill's speed. What you're basically suggesting is that if someone was to push you from behind while you were on the treadmill, they would be incapable of moving you forward. In fact, provided you match the treadmill's speed, you are an immovable object.

[In Focus]

Originally Posted by EgoFG

I am getting old .. but ...

The speed of light is relative to the observer. So if a vehicle is progressing at a good speed , the light from the headlights is traveling at the speed of light relative to the observer inside the vehicle, as well as relative to the observer on the side of the road.

That having been said the "wave property of light" proponents will mention "dopler shift" in light coming from distant galaxies (this it the crazy horn thingy - prolly got a diff name for light - it is when the waves compress to give a higher frequency).

but ordinary rules of physics do not really apply when an object (other than light) approaches the speed of light - IIRC, this is because the mass of the object approaches infinite, as the speed of an object approaches the speed of light - making empirical testing impossible.

Correct. It's not (theoretically) possible for an object with mass to hit light speed. If you were to get to that speed, then you (the object) would have infinite mass. You would also, I think, be the size of the universe.

If, however, you can find a way to reduce your mass to zero (ie, have no weight whatsoever), then I think you could achieve light speed.

[Spanrz]

Ok, here's one. One of my questions that I've just thought about for a while.

Going on the speed of light stuff.

If I look with a large Telescope at a star, do I gain an advantage on seeing the light before it hits earth?

[burnz]

Originally Posted by Spanrz

Ok, here's one. One of my questions that I've just thought about for a while.

Going on the speed of light stuff.

If I look with a large Telescope at a star, do I gain an advantage on seeing the light before it hits earth?

no you are still seeing with your eyes, weather it be a telescope or naked pays no relavance..

[ford man xf]

If you had access to a time machine would it be possible to go back in time and kill your parents or grandparents?