Even simpiler physics question

[dullard]

The air inside the car does NOT move with the car, at least not exactly with the car.

1) The car is not a closed system. Even with the vent fan off, there is a bit of air coming into the car from the vents and out of the car though the outlet holes.

2) The air itself has momentum (although it is small in comparison to the fly, you, or the car). Thus, even if the car was a closed system, the air will lag the car's motion by a little bit.

Also, the fly itself has momentum, and there will be a lag from the air's motion to the fly's motion (creating a dual lag from the car -> air -> fly). But, in the end, this whole thing is negligible on the fly's motion. As long as your car's vent fan isn't turned on full blast and as long as your windows and roof are closed, the fly won't be moving very far. It certainly will move, but not enough to really be noticible.

 

[torpid]

Originally posted by: Fritzo
If a fly is in a car with the windows rolled up, and it hovers in the center of the car, then the car starts moving, will the fly hit the back windshield or move along with the car because the mass of air inside the cabin is moving along with the car?

Neither. The fly will zip around the car erratically and annoy the piss out of everyone until you roll down the window and shoo it out.

 

[Fritzo]

Man, I don't feel so bad now. Guess it wasn't as easy as it seemed.

 

[dakels]

So if I have a remote control helicopter hovering in a vehicle and it accelerates to 50 mph. Does the remote control helicopter need to be capable of flying 50mph?

If I have a plane flying against the rotation of the earth at ~1040mph, is the plane hovering while the earth rotates underneath it?

 

[sdifox]

Where is Dr. Pizza?

 

[mesthead21]

I think the plane takes off of the treadmill

 

[child of wonder]

Originally posted by: dullard
The air inside the car does NOT move with the car, at least not exactly with the car.

1) The car is not a closed system. Even with the vent fan off, there is a bit of air coming into the car from the vents and out of the car though the outlet holes.

2) The air itself has momentum (although it is small in comparison to the fly, you, or the car). Thus, even if the car was a closed system, the air will lag the car's motion by a little bit.

Also, the fly itself has momentum, and there will be a lag from the air's motion to the fly's motion (creating a dual lag from the car -> air -> fly). But, in the end, this whole thing is negligible on the fly's motion. As long as your car's vent fan isn't turned on full blast and as long as your windows and roof are closed, the fly won't be moving very far. It certainly will move, but not enough to really be noticible.

This.

 

[blinky8225]

It will hit it as long as you're accelerating for a sufficient period of time. However, usually drivers only accelerate to a state of constant velocity. In this state, no force acts upon the fly, and it will stay put. Think how you only feel the seat pressing against your back when you're accelerating, but on the highway, when you're going a cool 55, you feel no force acting on you.

 

[Oyeve]

The fly weighs nothing. If the fly weigh a few ounces I bet it would splat to the rear. Weight is also a factor.

 

[MrPickins]

Originally posted by: Oyeve
The fly has very little mass. If the fly had a mass of a few hundred grams I bet it would splat to the rear. Mass is also a factor.

Fixed.

 

[silverpig]

What if the car is on a treadmill?

 

[GasX]

Newton's First Law: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

Thus the fly will not move unless the air pushes him.
The air will not move unless the car pushes on it.
Air is not an efficient transferer of force.
The fly will accelerate in the same direction as the car but at a lesser rate - at least until he flys off in a different direction

 

[spidey07]

The fly will actually move forward relative to the inside of the car. When you accelerate the air moves to the back of the car (well really just a tiny higher pressure). This will push the fly forward.

Now if it was a REALLY fat fly with more than a few grams of mass then he's gonna move backward because the force trying to move him (air) is not enough and he'll move backwards, relative to the interior of the car.

 

[silverpig]

Originally posted by: spidey07
The fly will actually move forward relative to the inside of the car. When you accelerate the air moves to the back of the car (well really just a tiny higher pressure). This will push the fly forward.

Now if it was a REALLY fat fly with more than a few grams of mass then he's gonna move backward because the force trying to move him (air) is not enough and he'll move backwards, relative to the interior of the car.

That is dependent on density, not mass. Flies are more dense than air, thus they go backwards.

 

[spidey07]

Originally posted by: silverpig

That is dependent on density, not mass. Flies are more dense than air, thus they go backwards.

True. Didn't even think about that.

So I'll revise and say fly goes backwards a little bit then has a "WTF is going on" moment and then start to fly forward until he hits the front windshield out of sheer panic.

 

[alkemyst]

stop being a freaking slob and clean your damn car!

 

[JTsyo]

I don't see why people think the fact that the fly is hovering makes a difference. Is the question really if the air will push the fly along with the car?

If your son is in HS, the fly will hit the rear since in HS we always ignore air effects =)

 

[Freshgeardude]

Originally posted by: MotionMan

Originally posted by: Brainonska511

Originally posted by: MotionMan

Originally posted by: Jeff7

Originally posted by: DisgruntledVirus
No it doesn't, because the fly uses the air in the vehicle to be able to fly. Since the air in the vehicle won't be moving since it's a sealed vehicle, the fly will remain in the same position.

Put a human in a spaceship. Accelerate the spaceship to 1/2 light speed. Splat.

If we could solve that inertia problem simply by sticking wings on a person, well, one major obstacle to high-speed space travel would have been solved long ago.

I think there may be a flaw in your analogy since people in space float, not fly.

I have never had a fly splat against my inside of my windshield or rear window.

MotionMan

The inside of the space ship is not a vacuum and gravity has nothing to do with your horizontal motion on the ground.

Vacuum or not, astronauts still cannot fly like a fly - they float due to a lack of gravity. Still, flies are not splatting against the inside of windshields or against rear windows.

MotionMan

Depending where the astronaut is. If in earth's orbit. There is gravity. How do you think they come back. They are just in a constant free fall around earth.

Now outside earth' orbit is different, but humans have yet to go further. The moon is still in earths orbit btw

 

[SMOGZINN]

The fly?s inertia will attempt to keep it in place as the car accelerates, the air will attempt to move the fly forward with the car. I think that at the slow speeds that a car accelerates which wins is mostly a matter of aerodynamics of the back end of a fly since the fly will have to move through the air to move backwards relative to the car. The more drag the fly?s ass generates, the less it will move relative to the ground.
Here is a simple test, put a fly in a jar and move it really fast. I guaranty that the fly will end up stuck to the back side of the jar. You don't see it happen in a car simply because cars accelerate fairly gently, but you can accelerate the jar much faster. Put that fly in a car with a huge acceleration and you would be cleaning flies off of your rear window.

 

[maziwanka]

Originally posted by: sdifox
frame of reference. The fly will be fine.

 

[DisgruntledVirus]

Originally posted by: freshgeardude

Originally posted by: MotionMan

Originally posted by: Brainonska511

Originally posted by: MotionMan

Originally posted by: Jeff7

Originally posted by: DisgruntledVirus
No it doesn't, because the fly uses the air in the vehicle to be able to fly. Since the air in the vehicle won't be moving since it's a sealed vehicle, the fly will remain in the same position.

Put a human in a spaceship. Accelerate the spaceship to 1/2 light speed. Splat.

If we could solve that inertia problem simply by sticking wings on a person, well, one major obstacle to high-speed space travel would have been solved long ago.

I think there may be a flaw in your analogy since people in space float, not fly.

I have never had a fly splat against my inside of my windshield or rear window.

MotionMan

The inside of the space ship is not a vacuum and gravity has nothing to do with your horizontal motion on the ground.

Vacuum or not, astronauts still cannot fly like a fly - they float due to a lack of gravity. Still, flies are not splatting against the inside of windshields or against rear windows.

MotionMan

Depending where the astronaut is. If in earth's orbit. There is gravity. How do you think they come back. They are just in a constant free fall around earth.

Now outside earth' orbit is different, but humans have yet to go further. The moon is still in earths orbit btw

Actually until you get beyond the gravitational influence of the known universe there is gravity, just it's so insignificant that it's effectively zero (although even then it's possible there are gravitational influences from other sources).

Even more so, until you exit our sun's gravitational influence (which is outside of our solar system) it's powerful enough to pull you in. That's why the planet (yes it is a planet btw) Pluto is orbiting the sun.

 

[dakels]

I keep thinking of theVomit Comet. The people and the plane are falling at the same rate giving the appearance of weightlessness. In reality, it is an illusion based on the plane relativelystationary to the person. When the plane decides to deviate from the fall and start moving back up, the people, of course, are put back on the surface of the plane as the plane pushes them up again. Would a super light balloon move with the plane as well?


On a more interesting note:

In Russia, commercial flights are offered on the Ilyushin Il-76 jet; several U.S. companies book flights on these jets.[7] The 1999 pornographic film The Uranus Experiment 1 had scenes filmed on such an aircraft; it is notable for containing the first instance of zero-gravity sex caught on film. - Wikipedia

must... see... this...

 

[edro]

Why do objects hanging from your mirror swing backwards when you accelerate?

The fly will move backwards if he does not compensate for the inertia.
It may not be noticeable at lower accelerations though.

Once the acceleration (or deceleration) is complete, the fly is free to move about without feeling any effects.

All objects inside the car (air included) feel the effects of the acceleration, because they "tend to stay in motion". (They are trying to stay in their current motion, which is "stopped")

 

[MotionMan]

Originally posted by: GasX
Newton's First Law: Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

Thus the fly will not move unless the air pushes him.
The air will not move unless the car pushes on it.
Air is not an efficient transferer of force.
The fly will accelerate in the same direction as the car but at a lesser rate - at least until he flys off in a different direction

Aren't we all "moving" with the Earth's rotation?

MotionMan

 

[Mo0o]

Could it be this?...

If the fly is in the middle of the car initially and just floating along and the car starts to accelerate, the fly will hit the windshield. But if you stop accelerating, I think the fly stops moving towards teh back of the windshield (relatively speaking)