Will it take off?

[fastTa]

Lets say you have a plane that could go 'exactly' the speed of light. You are standing inside of this plane with a laser. If you point it forward will light come out? You are already going the speed of light so how could the light go any faster? Now if you point it forward and walk backwards will it come out like a string? Seeing how you will be going a little slower than the speed of light? hmmmm... all these questions...

Easy. Einstein's special relativity laws cover this one.

Postulate 1:
The speed of light is the same for all observers, no matter what their relative speeds.

Postulate2:
The laws of physics are the same in any inertial (that is, non-accelerated) frame of reference. This means that the laws of physics observed by a hypothetical observer traveling with a relativistic particle must be the same as those observed by an observer who is stationary in the laboratory

The laser does not encounter air resistance as we know it, and it cannot supercede the speed of light....at least not as we humans are observing.

[2Fbodcru]

lol..... no forward air speed no take off! No air/wind over the wing no take off. Its as simple as that. Plus I got another one...

Lets say you have a plane that could go 'exactly' the speed of light. You are standing inside of this plane with a laser. If you point it forward will light come out? You are already going the speed of light so how could the light go any faster? Now if you point it forward and walk backwards will it come out like a string? Seeing how you will be going a little slower than the speed of light? hmmmm... all these questions...

http://imagine.gsfc.nasa.gov/docs/as...s/970102c.html
The Question
(Submitted January 02, 1997)

I looked all over but, this is the only place I found that may answer two questions of mine.


If I were traveling at the speed of light (out in space), and turned on a flashlight (facing forward), would it illuminate my console or will the light "stall"? Also, could I illuminate a target outside, if I turned on my headlights?
I believe this is the same question, just in a different setting. If I shot a bullet that travels at 600 ft/sec, and my car is speeding at the 600 ft/sec, would the bullet fly out of the barrel? Can the bullet actually accelerate to 1200 ft/sec?
Not only would I greatly appreciate the answers, I would really like to know a good place to learn this type of physics (like books, WEB, etc..)
Thanx!!!

The Answer
These are very good questions, and thinking about questions like these motivated Einstein to develop his Theory of Relativity. It will be easier to answer the second question first. In that case, the bullet would accelerate to 1200 ft/s relative to the ground. The reason is that the force of the gunpowder explosion increases the velocity of the bullet by 600 ft/s relative to the gun. If the gun happens to be traveling at 600 ft/s relative to the ground, then the final speed of the bullet relative to the ground will be 1200 ft/s. Keep in mind that essentially all speeds are relative to something else. For example, the Earth is rotating and moving around the Sun, so you are moving through space even when you are "at rest" relative to the ground.
I said "essentially" because there is one exception... the speed of light is always the same (specifically, 300000 km/s) to all observers , regardless of the speed of the observer or the light emitter (in this case, the flashlight). This is not very intuitive, as I hope the bullet explanation was. So even if you are traveling at 150000 km/s, a beam of light would still pass you going 300000 km/s or approach you going 300000 km/s. What happens is that as you travel faster and approach the speed of light, distances shorten and time slows down so that light still travels at 300000 km/s relative to you. This is not just a theory... these effects have been observed in experiments. According to Einstein's equations, it is impossible for anything with mass to reach the speed of light. So the answer to the first question is that you couldn't be traveling at the speed of light, but even if you were traveling at close to the speed of light, you would still be able to illuminate your console and shine a light on a target outside. The speed of a bullet is negligible compared to the speed of light, so in that case we don't have to worry about these effects.

A good general-level book on these topics is Einstein's Universe by Nigel Calder.

Andy Ptak
for the Ask an Astrophysicist team

[Jeff_in_Atl]

http://imagine.gsfc.nasa.gov/docs/as...s/970102c.html
The Question
(Submitted January 02, 1997)

I looked all over but, this is the only place I found that may answer two questions of mine.


If I were traveling at the speed of light (out in space), and turned on a flashlight (facing forward), would it illuminate my console or will the light "stall"? Also, could I illuminate a target outside, if I turned on my headlights?
I believe this is the same question, just in a different setting. If I shot a bullet that travels at 600 ft/sec, and my car is speeding at the 600 ft/sec, would the bullet fly out of the barrel? Can the bullet actually accelerate to 1200 ft/sec?
Not only would I greatly appreciate the answers, I would really like to know a good place to learn this type of physics (like books, WEB, etc..)
Thanx!!!

The Answer
These are very good questions, and thinking about questions like these motivated Einstein to develop his Theory of Relativity. It will be easier to answer the second question first. In that case, the bullet would accelerate to 1200 ft/s relative to the ground. The reason is that the force of the gunpowder explosion increases the velocity of the bullet by 600 ft/s relative to the gun. If the gun happens to be traveling at 600 ft/s relative to the ground, then the final speed of the bullet relative to the ground will be 1200 ft/s. Keep in mind that essentially all speeds are relative to something else. For example, the Earth is rotating and moving around the Sun, so you are moving through space even when you are "at rest" relative to the ground.
I said "essentially" because there is one exception... the speed of light is always the same (specifically, 300000 km/s) to all observers , regardless of the speed of the observer or the light emitter (in this case, the flashlight). This is not very intuitive, as I hope the bullet explanation was. So even if you are traveling at 150000 km/s, a beam of light would still pass you going 300000 km/s or approach you going 300000 km/s. What happens is that as you travel faster and approach the speed of light, distances shorten and time slows down so that light still travels at 300000 km/s relative to you. This is not just a theory... these effects have been observed in experiments. According to Einstein's equations, it is impossible for anything with mass to reach the speed of light. So the answer to the first question is that you couldn't be traveling at the speed of light, but even if you were traveling at close to the speed of light, you would still be able to illuminate your console and shine a light on a target outside. The speed of a bullet is negligible compared to the speed of light, so in that case we don't have to worry about these effects.

A good general-level book on these topics is Einstein's Universe by Nigel Calder.

Andy Ptak
for the Ask an Astrophysicist team

Ha! So I was right.

[TraceZ]

Back to the airplane discussion.

E40-

Imagine your Cessna parked on this hypothetical runway. you begin to give it throttle and the propeller pulls you forward. The computerized runway gizmo sees this and begins spinning the runway backwards.

Will this slow you down?? No. The propellor will continue to grab the air and pull you forward. The propellor does not care what the runway does.

The runway will see your increased speed and further increase its reverse speed to try and slow you down to no avail. Your propellor will continue to pull you forward.

To prove my point, imagine landing on a huge conveyor belt. It would be just like landing on flat land, only your wheel speed would be higher upon touching down. You'd be able to taxi to the end and exit the conveyor with a chirp of your wheels as they crossed the threshold. Steering would be very touchy, due to the increased wheel speed.

Or imagine that landing we made last year in the Dells on the glare ice with braking action null. If that slippery runway had been spinning on a conveyor it would not of made any difference. It was so slippery there was no traction anyways..

I know it's hard to believe it, but I am 100% positive i'm correct on this. The spinning runway computer will not be able to hold back the airplane. Think about it!! unless you were to tie the airplane to stationary ground with a rope, the airplane will move forward when the propellor is producing thrust.
How much force would it take to stand behind your airplane with a rope and hold it back? Now, put the airplane on a little treadmill and spin it, will the force on the rope go away?? No it wont!! The airplane will still go forward!!

[fastTa]

Tracy, you are missing the absolute fundamental in the entire principle that keeps aircraft aloft.........air velicity over the wings and body of the aircraft. Without this you absolutely cannot fly. The thrust alone produced by a plane does not contribute directly to lift, but instead provides the propelling force enough to give the aircraft enough velocity in order to experience the wind velocity and therefore the fluid dynamically dictated air pressures that provide lift.

As far as your conveyor belt theory making for a "flat ground" like landing. I assume you were trying to say that it would make for a "softer" landing. It will be just the opposite. If the conveyor belt runway was moving at an equal velocity to that of the aircraft but in the exact opposite direction, it would be relatively equivalent to that of doubling the landing speed of a conventional landing on a converntional runway.

[Jeff_in_Atl]

Tracy, you are missing the absolute fundamental in the entire principle that keeps aircraft aloft.........air velicity over the wings and body of the aircraft. Without this you absolutely cannot fly. The thrust alone produced by a plane does not contribute directly to lift, but instead provides the propelling force enough to give the aircraft enough velocity in order to experience the wind velocity and therefore the fluid dynamically dictated air pressures that provide lift.

I don't understand your point. In Tracy's example he will have air across the wing to give it lift.

[TraceZ]

Tracy, you are missing the absolute fundamental in the entire principle that keeps aircraft aloft.........air velicity over the wings and body of the aircraft. Without this you absolutely cannot fly. The thrust alone produced by a plane does not contribute directly to lift, but instead provides the propelling force enough to give the aircraft enough velocity in order to experience the wind velocity and therefore the fluid dynamically dictated air pressures that provide lift.

You are still missing it.

You are assuming that a moving runway can prevent an airplane from moving forward. It cannot! The airplane IS going to move forward and it will have air velocity over its wings.

[TraceZ]

I don't understand your point. In Tracy's example he will have air across the wing to give it lift.

Exactly.

[TruckMuddr]

Allright, I'm sure someone has a R/C plane and a conveyor belt

On a side note. I'm with Trace on this one. You can't look at the speed of the wheels since they aren't the source of pulpusion. they are just free spinning. All thats gonna happen is as the plane start to move forward the speed of the wheels and conveyor are gonna accelerate severely

[TruckMuddr]

Ok, I just found this, Thanks to another forum.

http://videos.streetfire.net/player....D-D6BA1A43A06B

Very generic, but proves a point

[TraceZ]

Ok, I just found this, Thanks to another forum.

http://videos.streetfire.net/player....D-D6BA1A43A06B

Very generic, but proves a point

Now that's what I'm talking about!

[bru333]

Allright, I'm sure someone has a R/C plane and a conveyor belt

On a side note. I'm with Trace on this one. You can't look at the speed of the wheels since they aren't the source of pulpusion. they are just free spinning. All thats gonna happen is as the plane start to move forward the speed of the wheels and conveyor are gonna accelerate severely

Exactly! The only way the wheels are gonna turn faster is if the plane is accelerating. The conveyor is just reacting to the increase in speed of the wheels so the plane has to be accelerating through the air, so it will eventually take off.

[Steel2686]

I still can't see how the plane would generate airlift when it's remaining in the same spot. If I am to understand this correctly, let's put this in perspective.

The plane is on a giant treadmill. The treadmill is moving at a speed in order to keep the plane in place. There is a person standing next to this giant treadmill, but not on the belt. Is the plane moving past this person, or is it staying in the same position? How can air be generated from this?

[TraceZ]

The treadmill is moving at a speed in order to keep the plane in place.

The treadmill cannot keep the plane in place. It is imposible. The plane will move forward and generate lift to take off.

Watch the skateboard video again. No matter how fast he pulls the paper out from under the skateboard it still accelerates forward at the same rate.

There is a person standing next to this giant treadmill, but not on the belt. Is the plane moving past this person, or is it staying in the same position? How can air be generated from this?

The plane is moving past this person, just as it would on a standard runway.

[Jeff_in_Atl]

I still can't see how the plane would generate airlift when it's remaining in the same spot. If I am to understand this correctly, let's put this in perspective.

The plane is on a giant treadmill. The treadmill is moving at a speed in order to keep the plane in place. There is a person standing next to this giant treadmill, but not on the belt. Is the plane moving past this person, or is it staying in the same position? How can air be generated from this?

Well that gets back to my first post. Is the plane moving or not. The question is contradicting itself and therefore invalid.