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# [BBC]The quest to fly from New York to London in one hour - Page 6

Quote:
Originally Posted by Manyak

Angular velocity has nothing to do with this, and no your angular velocity doesn't stay the same. If you are standing exactly on the pole and take one step forward, then take two steps backwards, your angular velocity just went in the completely opposite direction.

This is simply not correct. Your angular velocity standing on the poles is the same as someone on the equator. (Your radius traveled is smaller at the poles.) No matter where you stand on Earth your angular velocity will be constant. If you take one step forward from the pole and then take two steps back (stepping back over the pole and onto the other side) your direction w.r.t. the rotational axis has not changed. Your position on the unit circle has changed and your radius has changed, but not your angular velocity. Unless stepping onto the other side of the pole suddenly sends the Earth spinning clockwise, it is not suddenly negative. Therefore, when I travel on Earth I do not have to accelerate or decelerate to compensate for Earth's rotational velocity.
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Well, this thread makes it clear that a nice side effect of this technology ever becoming mainstream is that a lot of people will be forced to become educated in basic physics.

I love the egos on some of you.
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Man...read your own sentence carefully. Leaving the earth's gravitational field requires a certain speed, not acceleration. That's why spaceships orbit the earth a few times before escaping into space, because the acceleration is low enough that it takes that long to ramp up the speed.

But regardless, your question has nothing to do with escape velocity. To maintain a certain speed, net forces have to be >= 0. If net forces are 0, then acceleration is also 0. The moral of the story is that high-speed vehicles require a great amount of force to maintain their speeds, but because the net force is always close to 0, it won't be felt at all.

First off, it is escape velocity; not speed. Secondly, to generate the force necessary to attain escape velocity, acceleration is necessary. Only once escape velocity has been achieved can acceleration be reduced to zero as to maintain the constant velocity. At this point, a "great amount of force" is not necessary to maintain a given velocity because of inertia. Friction is a negative vector force however, and acceleration is equal to the sum of all the forces over the mass. Therefore, acceleration is necessary to maintain a positive thrust vector force to oppose gravity so that ΣF=0. Also, rockets orbit the Earth several times after launch as a cheap way to gain the needed acceleration using gravity.

I also was not making a direct analogy between super sonic flight and escape velocity, I used it as an example of a threshold for clarification.
Quote:
Depending on the shape of the airframe, there might be a very slight acceleration when moving from transonic to supersonic speeds as the airflow becomes more uniform, but you probably would not feel it. Some parts of the aircraft break the sound barrier before others. For example, on aircraft with thick wings and a narrow fuselage, airflow over the wings would become supersonic before airflow over the rest of the aircraft. Once the entire aircraft reaches >Mach 1, the handling characteristics change.

Drag increases proportional to your speed until you approach Mach 1. When you get close to Mach 1, a shock wave forms in front of your aircraft, dramatically increasing drag and requiring more thrust from your engine to overcome that drag (ie you need more force to generate the same amount of acceleration). As you go beyond Mach 1, the increase in drag is once again proportional to the speed of the aircraft. The shockwave is still there and it's still creating lots of drag, but you don't see another sudden dramatic increase like you did when moving from subsonic to transonic speed.

Thank you for answering my question.
Edited by Solarin - 10/14/12 at 11:13pm
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Quote:
Originally Posted by Solarin

This is simply not correct. Your angular velocity standing on the poles is the same as someone on the equator. (Your radius traveled is smaller at the poles.) No matter where you stand on Earth your angular velocity will be constant. If you take one step forward from the pole and then take two steps back (stepping back over the pole and onto the other side) your direction w.r.t. the rotational axis has not changed. Your position on the unit circle has changed and your radius has changed, but not your angular velocity. Unless stepping onto the other side of the pole suddenly sends the Earth spinning clockwise, it is not suddenly negative. Therefore, when I travel on Earth I do not have to accelerate or decelerate to compensate for Earth's rotational velocity.
I love the egos on some of you.
It's not ego, and has entirely nothing to do with myself. It's simply the belief that everyone could benefit from an understanding of basic physics. You obviously have a certain amount of understanding of these concepts, so I'm confused why you have trouble grasping a basic concept such as the difference between force and acceleration.
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First off, it is escape velocity; not speed.
Wrong. Escape velocity is a misnomer, as it is simply a measure of kinetic energy required to leave a planet's gravitational field (KE = GPE), assuming no friction forces. It doesn't matter what direction you're moving in, as long as you're not moving toward earth.
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Secondly, to generate the force necessary to attain escape velocity, acceleration is necessary. Only once escape velocity has been achieved can acceleration be reduced to zero as to maintain the constant velocity. At this point, a "great amount of force" is not necessary to maintain a given velocity because of inertia. Friction is a negative vector force however, and acceleration is equal to the sum of all the forces over the mass. Therefore, acceleration is necessary to maintain a positive thrust vector force to oppose gravity so that ΣF=0. Also, rockets orbit the Earth several times after launch as a cheap way to gain the needed acceleration using gravity.
If ΣF=0, there is no acceleration, but you will still be moving because of Newton's first law, which is why a great amount of force is necessary at high speeds; to maintain zero net forces, you need a force that equals the opposite of the drag forces, which can be great, depending on your speed. I can tell you understand this, which makes me think I simply don't understand the point you're trying to make. "Acceleration is necessary to maintain a positive thrust vector force to oppose gravity so that ΣF=0" -- you're obviously not talking about the acceleration of the vehicle, because if ΣF=0, then there is no acceleration.
Quote:
Originally Posted by MintMouse

any speed, even
True
Edited by flamingoyster - 10/15/12 at 11:28am
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We've always been able to fly from New York to London in 1h.

London, Ontario.
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Quote:
Originally Posted by Solarin

...

At this point I call troll.
Edited by Manyak - 10/15/12 at 1:51pm
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Quote:
Originally Posted by Manyak

At this point I call troll.

Agreed.

I find it quite hard to believe one can have as much understanding as he shows, while completely dismissing rudimentary physics. If not trolling, the ignorance boggles the mind.
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Quote:
Originally Posted by Solarin

Your linear velocity with respect to the Earth would be zero, but your angular velocity would not be zero. Angular velocity is constant at all points on the Earth. Therefore, you don't accelerate (or decelerate).
Perhaps I wasn't phrasing my question correctly.
When you are approaching the speed of sound, can you slowly accelerate up to and past that speed, or does an acceleration threshold need to be met because of drag forces? (Like escape velocity of the Earth.)

Breaking the sound barrier requires extra force or special aerodynamics. For instance if MACH 1 = 700 mph (MACH 1 varies) to accelerate from 699 to 701 mph requires a lot more force than 697 to 699. This is due to shock wave formation. Source : Graduate aerodynamics class
Quote:
Originally Posted by Lumo841

Breaking the sound barrier requires extra force or special aerodynamics. For instance if MACH 1 = 700 mph (MACH 1 varies) to accelerate from 699 to 701 mph requires a lot more force than 697 to 699. This is due to shock wave formation. Source : Graduate aerodynamics class

I don't claim to have any amount of great understanding of physics (although it fascinates the hell out of me and it's what I want to go back to school for) but if breaking the sound barrier requires "extra force" or "special aerodynamics" then where were either of those factors for Felix when he broke it simply by falling? If acceleration due to gravity is a constant (I think, haven't studied physics in a decade), then where was the extra force you speak of? He was also not very aerodynamic as when he hit 833.9mph, he was tumbling end over end.

Again, I'm not claiming I know more than anyone else in here, and in fact I think I DON'T, therefore this question isn't to antagonize, I'm just genuinely curious.
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Quote:
Originally Posted by Lumo841

Breaking the sound barrier requires extra force or special aerodynamics. For instance if MACH 1 = 700 mph (MACH 1 varies) to accelerate from 699 to 701 mph requires a lot more force than 697 to 699. This is due to shock wave formation. Source : Graduate aerodynamics class

You do realize that it's going to fly 350km up, right? There is pretty much no air that high, so there is no need to worry about aerodynamics. They can send a brick that fast at that altitude if they wanted to and it wouldn't require any more power than what it takes to get something that is aerodynamic up to those speeds.
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Quote:
Originally Posted by andrews2547

You do realize that it's going to fly 350km up, right? There is pretty much no air that high, so there is no need to worry about aerodynamics. They can send a brick that fast at that altitude if they wanted to and it wouldn't require any more power than what it takes to get something that is aerodynamic up to those speeds.

That's a bit of an exaggeration. There is still an atmosphere, so there is still friction. Sure it's less, but not ignorable.
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