Physics with Falcon (and others)

Reading the SR71 thread make me think of this because someone mentioned planes being capable of 8,000 mph…

So, let’s say a plane goes 8,000 mph and it fires a missile that is capable of travelling on its own at 2,000 mph. 
 

What happens?

1) The missile is fired and immediately goes backwards at 6,000 mph relative to the plane?

2) The missile goes forward at 10,000 mph?
 

3). The missile goes forward initially, then gradually slows down to 2,000 mph?

(I’m guessing #3)

Wouldn’t it be #3 but acceleration would be brief ? The missile is starting with the momentum of the plane … right ? Aerodynamics would affect the rate it decelerates as you said . 

The missile would begin deaccelaration immediately because the force opposing its forward velocity (aerodynamic drag) would be enormously higher than the force propelling its forward velocity (the force of the engine). It would slow down until those forces net to zero, at 2000 mph.

I don't think it would end well.

An object designed for 2,000 MPH entering at 4 times it's designed speed would probably get weird. 

It gets "released" the plane will slightly accelerate due to less drag and the missile will slow down till its own thrust can propell it at its top speed of 2,000

It's not like a bullet being shot from a barrel.

Think of holding your hand out the window of a car. And dropping a rock. You're just letting go. If it doesn't have propulsion to keep up, it just falls back

Falcon

in case you didn’t see this in ‘moto related’..,

What speed does the roost hit us at when following a dirt bike?

This is a really interesting physics question. 

Factors that I can think of:

1.  The speed of the following rider is the first thing to factor in. If the roost was stationary in the air you’d be hitting it at that speed.  That’s the minimum. Say, 40 mph?

2. Is it the case that there’s no rearward propulsion of roost unless there is a loss of traction and the tyre moves faster that the tyre’s ‘normal’ ground speed?

3. The lead bike’s wheel rpm (when traction is lost) must come into it. That faster that wheel is spinning, the faster it will propel the roost towards the approaching rider.

4. That rearward roost velocity must surely be related to wheel radius which will decide the linear speed the knobs (at the tyre circumference) are travelling.

5. And how high does the rear wheel rpm rise when it has no traction?

6.  Is the speed of the front rider relevant? On one hand, the dirt is never travelling forward due to that bike’s movement, only backwards due to that machine’s rear wheel spin.  On the other hand, the faster mph that lead bike is travelling, the faster the knob speed if it loses traction. Or is that not relevant?

7.  Ultimately, the roost impact speed must surely be the sum of the approach speed of the second bike plus the lead bike’s rearward wheel knob velocity?

What do you reckon, Falcon?

If the rear wheel speed of the front bike is say 30mph in first gear max, then you'd have to subtract the bikes forward speed, I would guess. 

I'd say I'd agree with most of that. However I can't get on board with it's related to the radius.

I think we have to define roost. My personal definition is "the debris that the tire pushes from the ground

to propel the bike forward". That eliminates the errant debris that's stuck to the tire/wheel and gets propelled

off when the centripetal(?) force becomes greater than the sticky or friction between 2 knobs holding it in place.

So basically a shoveling effect vs  just being stuck to the tire. For conversation lets call lead rider A and following rider B.

So let's say rider A is in 3rd gear and going 35mph and lands on the top of a double but gets on the gas just before and

the rear wheel touches the ground at a speed of 55. the net effect is the wheel is pushing the dirt at 20mph rearward. But,

some of the dirt will go straight back and some will go upward. the going straight back will be closest to the 20MPH, as the

angle changes part of the velocity is lost going in an upward direction vs straight back. Then add the speed of the oncoming rider B and you get "ouch". So if Rider B is also going 35mph rider B would experience being hit with roost at 55mph.

Now a more powerful bike would plow more debris to get the bike going because the less powerful bike would have the tire

slowed down faster by friction to the ground and not be able to shovel as much dirt. So while initially the speed would be the same, the volume of roost you experience is far worse.

And on a side note, A bike going 50MPH that has a rock stuck between the knobies on the front tire that happens to let loose at just the right time to go straight forward would leave the tire at 100MPH velocity.

Mr. Falcon,

Being of physics leaning, do you believe we exist in a simulation?

TM

The gummies kicked in?

Statistically, we're more likely existing in a simulation than not. As our computers advance, you're going to see the next level of simulation. So how do you know we're not just 1 simulation level above?

TM