Something I have always wondered.

ScarySquirrel

ScarySquirrel

ScarySquirrel

Soldato
Joined
13 Jan 2004
Posts
23,795
Location
South East
Ok, imagine you are driving a car with the windows open at a constant speed of 20mph. Next to the car a bird/rc plane is flying at the same speed, 20mph.

Let's say the bird/rc plane veers into the car through the window maintaining the same speed, would the bird/rc plane

a)keep flying at the same speed but inside the car
b)suddenly fly forward into the windscreen



Also, imagine the same scenario but with a convertible, what would happen then?

Thanks.
 
ScarySquirrel said:
Ok, imagine you are driving a car with the windows open at a constant speed of 20mph. Next to the car a bird/rc plane is flying at the same speed, 20mph.

Let's say the bird/rc plane veers into the car through the window maintaining the same speed, would the bird/rc plane

a)keep flying at the same speed but inside the car
b)suddenly fly forward into the windscreen



Also, imagine the same scenario but with a convertible, what would happen then?

Thanks.
Click to expand...

It would smash into the rear windscreen as the movement into the car would reduce the plane's forward facing vector, i.e. some of the planes speed would be "spent" on moving into the car
 
ScarySquirrel said:
Ok, imagine you are driving a car with the windows open at a constant speed of 20mph. Next to the car a bird/rc plane is flying at the same speed, 20mph.

Let's say the bird/rc plane veers into the car through the window maintaining the same speed, would the bird/rc plane

a)keep flying at the same speed but inside the car
b)suddenly fly forward into the windscreen



Also, imagine the same scenario but with a convertible, what would happen then?

Thanks.
Click to expand...

IMO a)

but confused by turblence issues, TTIUWE (e=experimentation! :D )
 
Very good question. Also, imagine your standing up on a bus. If you were to jump, so that no part of your body was touching the bus, then what would happen? Would the bus continue forward around you until you slam into the back of the bus. Obviously this wouldn't happen, but why not?
 
The bird/plane would move forwards slightly relative to the car as wind resistance has decreased but lack of airflow over the wings would quickly cause it to drop into the footwell/front seat of the car.

This assumes that the bird/plane was able to enter the car cleanly without crashing into the door due to turbulence around the vehicle.
 
b as the air inside the car is stationary when compared with the speed of the car. ie, if you throw a ball whilst travelling in a car, its relative speed will be the speed you throw it forwards at, it wont return back to you as it has a constant speed of the car.

The plane would act as if it had entered stationary environment, so it would move forward into the windscreen.

I have a degree in bull-excrement.
 
the plane would drop to the floor as it would no longer be moving relative to the air, the bird would have to flap a lot harder and probably do a poo

edit: ok it might move forward a bit but i doubt it could gain enough speed to achieve lift
 
Last edited:
Alex UK said:
Very good question. Also, imagine your standing up on a bus. If you were to jump, so that no part of your body was touching the bus, then what would happen? Would the bus continue forward around you until you slam into the back of the bus. Obviously this wouldn't happen, but why not?
Click to expand...

When on a bus you are travelling at the same speed as the bus. When you jump you are still moving forward at the speed of the bus therefore don't move backwards. It's like if you jump on earth you don't leap frog a couple of counties because everything on the surface of the earth is moving at the same speed as the earth.
 
Slam62 said:
the plane would drop to the floor as it would no longer be moving relative to the air, the bird would have to flap a lot harder and probably do a poo

edit: ok it might move forward a bit but i doubt it could gain enough speed to achieve lift
Click to expand...


i think i'll go with that.
 
Alex UK said:
Very good question. Also, imagine your standing up on a bus. If you were to jump, so that no part of your body was touching the bus, then what would happen? Would the bus continue forward around you until you slam into the back of the bus. Obviously this wouldn't happen, but why not?
Click to expand...
This was sort of question is asked nearly every week on up all night (five live) with Doctor Karl.
Something to do with inertial frame of reference.
 
After trying to think way way back to my A level Physics, I'd have to say:

c) it depends on air turbulence, friction and wind resistance

If there was no air turbulence or air friction, a vacuum, and both object were travelling at 20mph, velocity not speed, as you'll need to include direction into this equation. The relative velocity between a stationary object and each of the two travelling objects would be 20mph, but the relative velocity between the two moving objects would be zero (ie, both moving in the same direction at the same speed), so when the moving plane entered the moving car, the relative velocity would remain the same, so it would appear that the plane would be hovering inside the car.

And now the real world:

Given the plane is moving at 20mph, the air/friction hitting the plane would also be 20mph, hitting the nose. The air inside the car, is also moving at 20mph, but in the SAME direction as the plane, so as the plane enters the car, the air friction on the plane would reduce dramatically, and if the power to the plane's engines remained the same, then it would hit the windscreen because it would increase in speed. Similar to hitting a jetstream I suppose, less power is needed to attain the same speed.

But if the plane was controlled so that the ground speed was constant, then as it entered the car, the power to the engines would reduce, to keep the speed constant. Think of flying birds, they always fly in a V formation, with the bird in front reducing wind resitance to the bird behind, it's acting like a windscreen.

Maybe.

:confused:
 
but if your runnign along side the bus, then get onto the bus, still running, you wont stop still will ya, youd smash your face into the window. The bird is not attached to the car in anyway and would still be flying at 5mp faster than the car is moving, and so would hit the window,

imo

oops -re-read the OT and i see it says they both move at 20mph - sure it said the bird was moving at 25mph. in that case the bird would remain in the location it was relitive to the car before it entered. of course the fact there is no free moving air would not help and it would, having a bit of a brain, fly out the window or take a seat and let the car take the strain.
 
Last edited:
I'll expand. You jump inside a bus travelling at 30mph, but due to your contact with the bus you are travelling at 0mph relative to the bus.

Taking an RC plane and a car, the plane is travelling at 0mph relative to the car, however the ability to fly is dependent on the air speed over the wings. As the plane enters the car, it will continue to do the same speed as the car briefly, but lose it's ability to fly as the airspeed over the wings falls to 0mph.
It would therefore have a burst of acceleration forward in the car while falling at the same time.
 
Alex UK said:
Very good question. Also, imagine your standing up on a bus. If you were to jump, so that no part of your body was touching the bus, then what would happen? Would the bus continue forward around you until you slam into the back of the bus. Obviously this wouldn't happen, but why not?
Click to expand...
If you jumped Matrix-style, then you would hit the back of the bus. Whilst you're stood up, the bus is moving you at the same speed as the bus. Once you jump, the bus stops being the thing giving you kinetic energy, and you'd begin to slow down, but you'd slow down gradually, so I assume you'd move back fractionally, but not by much.
 
Is this the same sort of thing as the question "if you were in a lift and it dropped very fast, if you jumped just as it was about to hit the floor, would you be ok"
 
Baldyman said:
If you jumped Matrix-style, then you would hit the back of the bus. Whilst you're stood up, the bus is moving you at the same speed as the bus. Once you jump, the bus stops being the thing giving you kinetic energy, and you'd begin to slow down, but you'd slow down gradually, so I assume you'd move back fractionally, but not by much.
Click to expand...

I doubt you would slow down much as generally what would slow down your velocity outside a bus would be air resistance but seeing as the air in the bus is also moving at 30mph with you then there would be no air resistance to slow you down. Now if the bus was constantly accelerating and you jumped then you'd hit the back if you stayed up there long enough as you'd be going at 30mph still and the bus would be increasing in speed.

The answer to the planes already been said. It would lose air resistance and thus its lift so it would fall down into the car and forward slightly as it tries to gain speed.

It would be the same effect as dropping the plane in the car with its engines going but both at 0mph.
 
You must log in or register to reply here.
Back
Top Bottom