Question about speed and vehicles

[Sundown444]

Say a super fast car is going car is going at twice the speed of sound, an there is an aircraft going at the same speed. Normally, maneuvering and controlling at high speeds (slowing down, speeding up, stopping and changing direction) is very hard. Now, I just want to make sure by asking, what factors make it hard for the car and aircraft to control at high speeds?

 

[anorlunda]

Think of Newton's second law. F=ma. Express it as a=F/m. To produce a specific acceleration a you need a specific ratio of F to m. There is no v in that equation. So accelerating/decelerating a fast moving body is no different than for a slow moving body.

Changing or reversing direction is a different question. Why do you think it is more difficult to reverse a body moving at a velocity of 1, compared to reversing a body moving at a velocity of 100?

 

[rootone]

It's a lot easier to control an aircraft at supersopinic speed because air does not have solid objects and turns to deal with.
While it's not impossible for a car on the ground to go that speed, finding a suitable place to do that without a disaster is not easy.

 

[Sundown444]

What I am asking is what properties and aspects that affect movement affect high speed maneuvering? Kinetic energy? Momentum? Inertia? And anything else?

 

[Sundown444]

Think of Newton's second law. F=ma. Express it as a=F/m. To produce a specific acceleration a you need a specific ratio of F to m. There is no v in that equation. So accelerating/decelerating a fast moving body is no different than for a slow moving body.

Changing or reversing direction is a different question. Why do you think it is more difficult to reverse a body moving at a velocity of 1, compared to reversing a body moving at a velocity of 100?

Not sure. You know why?

 

[anorlunda]

Reversing a body with speed 1 means a net speed change of 2. (changing speed +1 to -1 is a net change of 2)
Reversing a body with speed 100 means a net speed change of 200.

 

[Sundown444]

Reversing a body with speed 1 means a net speed change of 2. (changing speed +1 to -1 is a net change of 2)
Reversing a body with speed 100 means a net speed change of 200.

Could you go into more detail about that, please? And what about for changing direction rather than reversing it?

 

[anorlunda]

Let's start with you. What have you studied about physics and mechanics? I don't want to give answers you don't understand.

 

[rootone]

The same physics applies both to land vehicles and aircraft.
In military scenarios and games aircraft are highly maneuverable units, but not by themselves able to capture territory.

 

[Sundown444]

Let's start with you. What have you studied about physics and mechanics? I don't want to give answers you don't understand.

I do understand some physics. Like Centripetal Force, mass times velocity squared over radius of turn. Need I say more?

 

[rootone]

what factors make it hard for the car and aircraft to control at high speeds?

https://en.wikipedia.org/wiki/Aerodynamics

 

[Sundown444]

https://en.wikipedia.org/wiki/Aerodynamics

Aerodynamics, huh? Could you give a shorter version as to why?

 

[rootone]

You were asking what sort of factors need to be considered for designing a supersonic vehicle?

 

[Sundown444]

You were asking what sort of factors need to be considered for designing a supersonic vehicle?

No, just factors that make it hard to control supersonic vehicles.

 

[anorlunda]

Need I say more?

Yes, I said 1+1=2 and you asked me to elaborate. Do you not understand that?

 

[Sundown444]

Yes, I said 1+1=2 and you asked me to elaborate. Do you not understand that?

I knew that. That wasn't what I was asking about. I meant what you meant in net speed change? I thought you meant net unbalanced force or something, but I could be wrong. I heard of net unbalanced force, but not net speed change.

 

[Sundown444]

Yes, I said 1+1=2 and you asked me to elaborate. Do you not understand that?

Now I get what you mean by net speed change. So, is inertia the main factor as to why the vehicles would be hard to control? What about friction and aerodynamics?

 

[rootone]

No, just factors that make it hard to control supersonic vehicles.

It's not that hard but flight controls become hugely more sensitive at supersonic speed and a few millimeters of change are important.
At subsonic speed, typically passenger aircraft say, a few centimeters movement of a wing surface is sufficient for control

 

[Sundown444]

It's not that hard but flight controls become hugely more sensitive at supersonic speed and a few millimeters of change are important.
At subsonic speed, typically passenger aircraft say, a few centimeters movement of flight of control surface is sufficient for control

So why do the controls become more sensitive at supersonic speeds?

 

[rootone]

I'm no expert, but I think the answer is that a craft moving at supersonic speed is now facing head on collision with air molecules,
There no longer is any buffer of compressed air ahead of it, well not as much,

 

[Sundown444]

I'm no expert, but I think the answer is that a craft moving at supersonic speed is now facing head on collision with air molecules,
There no longer is any buffer of compressed air ahead of it, well not as much,

I see.

So what about inertia and friction? How do those affect control of such vehicles at high speeds?

 

[rootone]

As far as I know inertia does not enter into it,
friction does increase with speed though, I think that contributed to commercial SSTs being uneconomic (cool idea though)

 

[Sundown444]

As far as I know inertia does not enter into it,
friction does increase with speed though, I think that contributed to commercial SSTs being uneconomic (cool idea though)

I believe you mean air resistance. I meant ground friction.

 

[anorlunda]

Your original question was for car or airplane, so I assume you are not asking about aerodynamics.

Normally, maneuvering and controlling at high speeds (slowing down, speeding up, stopping and changing direction) is very hard.

Not true. The amount of speed change might be larger, but the effort to change speed, or accelerate are the same at any speed. That's why I pointed you to the equation F=ma in post #2. F=ma does not change with speed. Do you understand that or not?

 

[Sundown444]

Your original question was for car or airplane, so I assume you are not asking about aerodynamics.Not true. The amount of speed change might be larger, but the effort to change speed, or accelerate are the same at any speed. That's why I pointed you to the equation F=ma in post #2. F=ma does not change with speed. Do you understand that or not?

I understand that. But forget I said the very hard part. I just want to know what factors affect control and maneuvering in vehicles at high speed, whether it be inertia or some other things. That is all I am asking. I wasn't asking about inertia alone, you know.

 

[rootone]

Well here is something to consider,
https://en.wikipedia.org/wiki/Gravity_assist

 

[Nidum]

Many factors affect the manoeuvring rates of aircraft . In the limit though it comes down to power to weight ratio , structural strength and stability .

For any actual aircraft design there will be a set of performance charts defining the acceptable combinations of the several different factors affecting specific flight manoeuvres .

 

[Nidum]

Just note though that with modern high performance aircraft such as fighters and stunt specials the limit on manoeuvring rates is usually set by the maximum g level which the pilot can tolerate rather than by any limitations of the actual aircraft design .

 

[anorlunda]

I still don't understand the question. Please clarify. Are you asking about airplanes in the air, or about any fast moving object whether in air or space?

Inertia does not change with speed.

 

[Sundown444]

I still don't understand the question. Please clarify. Are you asking about airplanes in the air, or about any fast moving object whether in air or space?

Inertia does not change with speed.

I knew that, but I wasn't asking about just inertia.

Ans yes, I meant air and space.

 

[anorlunda]

I meant air and space.

That makes it easier, because in space we don't have to talk about drag from the air.

So the answer is no, faster motion is not harder to control. You can stop asking what factors make it harder, because it isn't harder.

Especially in space, get used to thinking of different frames of reference. An object moving fast in one frame is moving only slowly in a second frame, and not moving at all in a third frame. Yet the laws of physics remain the same in all frames. The difficulty of maneuvering a heavy object is the same in all frames. That is the kind of thinking (plus light speed) that eventually led Einstein to the special theory of relativity.

 

[Sundown444]

That makes it easier, because in space we don't have to talk about drag from the air.

So the answer is no, faster motion is not harder to control. You can stop asking what factors make it harder, because it isn't harder.

Especially in space, get used to thinking of different frames of reference. An object moving fast in one frame is moving only slowly in a second frame, and not moving at all in a third frame. Yet the laws of physics remain the same in all frames. The difficulty of maneuvering a heavy object is the same in all frames. That is the kind of thinking (plus light speed) that eventually led Einstein to the special theory of relativity.

So the question should have been about mass, not speed, then? I could be wrong, but still...

Are you sure about the speed thing, though? I was also wondering about how it can be difficult to stop an object and changing direction. Momentum is how difficult something is to stop, and that is dependent on velocity. There is also friction and fluid friction (the latter is not used for space), especially the former being needed to come to a stop on the ground, and from what I have learned, kinetic energy quadruples with speed, which not only quadruples kinetic energy, but also stopping distance, if I recall correctly. Speaking of changing direction, centripetal acceleration is quadrupled with velocity, so the more velocity, the centripetal acceleration is quadrupled, and this, in terms of centripetal force (with mass added), more force is required to make centripetal acceleration happen.

 

[anorlunda]

If you keep changing the question I'm losing interest in answering. But one last time.

Remember the delta $v$ from post #6? Let's put it in terms of momentum which is $mv$. Start at time 1 with momentum $mv_1$ then change to momentum $mv_2$. The mass stays constant but velocity changes. Then the change in momentum is $m(v_1-v_2)$ If you let $v_2$ equal zero than means stopping. If you let $v_2=-v_1$ then we reversed direction.

The point is that the effort or work we need to do depends on the change in velocity, not the value of $v_1$. So $v_1$ big means fast, $v_1$ small means slow. $m(v_1-v_2)$ is the same starting fast or slow. But stopping a fast object is more change in $v$ than for a slow object. But different observers moving at different speeds will disagree about what speed means stopped. So to say it observer independently, it is only the change that matters, not the initial velocity.Do you understand now?

 

[Sundown444]

If you keep changing the question I'm losing interest in answering. But one last time.

Remember the delta $v$ from post #6? Let's put it in terms of momentum which is $mv$. Start at time 1 with momentum $mv_1$ then change to momentum $mv_2$. The mass stays constant but velocity changes. Then the change in momentum is $m(v_1-v_2)$ If you let $v_2$ equal zero than means stopping. If you let $v_2=-v_1$ then we reversed direction.

The point is that the effort or work we need to do depends on the change in velocity, not the value of $v_1$. So $v_1$ big means fast, $v_1$ small means slow. $m(v_1-v_2)$ is the same starting fast or slow. But stopping a fast object is more change in $v$ than for a slow object. But different observers moving at different speeds will disagree about what speed means stopped. So to say it observer independently, it is only the change that matters, not the initial velocity.Do you understand now?

Sorry. I didn't mean to change the question. I thought it was clear enough, but it wasn't. My bad.

And yeah, I understand. Thanks.