If a fly is in a lift does it have to fly up when the lift goes up?

Answer 1

For anything to rise against gravity needs a force to be applied. That's why you feel a slightly greater pressure in your legs as the lift rises.

A fly in flight is already having to apply a certain amount of force to the air around it, just to stay aloft. As the lift rises, this will have to increase to accelerate the fly upwards.

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And I can't believe Snapping Monster and the others putting forward this false argument! You don't seem to recognise the difference between a frame of reference moving horizontally at a steady speed - which, I agree, doesn't have any accelerative forces that a stationary one doesn't - and one that is accelerating upwards.

When you pull away from the lights in your car, are you pushed backward in your seat? So if a bird was flying in the car as you accelerated, what would happen? Answer: it has to accelerate - either by flying forwards or, as you are, being pushed forward by the fabric of the car. If it doesn't, it's a feathery splat on the rear window. Or in the opposite case, what happens to anything unsecured in a car which brakes suddenly? Answer - it flies forward.

Equally, what happens if you're going up a hill in your car and take your foot off the accelerator? Does it carry on in a steady state, as it would on a level surface (forgetting friction, air resistance etc)? No - it starts to lose speed. A vertically-moving frame is DIFFERENT to a horizontal one. At least you and chopchubes admit the acceleration phase is different, but you DO weigh more in a rising lift because you are constantly having to have a force applied, over and above what the floor would do on its own: if you weren't, you couldn't gain the gravitational energy, mg(h2-h1).

Nothing accelerates without a force being applied. Newton knew that 300 years ago. Equally, the gentleman called Einstein (mentioned by SM) pointed out nearly a hundred years ago that moving against a gravitational gradient was like accelerating. Follow what they say, not people who haven't really thought about the problem.

Nothing gains gravitational potential energy without using some other kind of energy (or having other energy expended on it). When a lifting force is applied to us, we feel it in our leg joints. When one is applied to a fly in flight, it must feel it, primarily through its wings. It doesn't have to gain any speed through the air, but it DOES need to accelerate.

Answer 2

Can't BELIEVE some people have said it would have to fly up to stay at the same place in a lift! If you were in a car with the windows up and a bird was in the car flying would it have to go at the speed of the car to avoid getting crushed against the rear window! NO it would NOT geez!

The fly if it was in a holding position, lets say flying in a little circle would not have to fly 'up' to maintain that position in the lift. It WOULD have to compensate for the acceleration. That moment when the lift starts and everyone feels heavier for a moment, the fly would seem to lose some height as it felt the same thing. A gentleman called Einstein remarked on how acceleration was the same as gravity in case anyone is interested. When the lift is going at a steady rate the fly will not need to exert any more effort than as normal to maintain a certain height relative to the lift.

Answer 3

If the lift is enclosed, the air inside the lift will travel at the same speed as everything else inside the lift and, no, the fly won't have to fly up.

If the lift is a cage type lift exposed to the outside air, then yes the fly will have to fly up because the lift is passing through the air.

Considering the enclosed type lift:
As the lift accelerates upwards, the fly (and everything else in the lift) will momentarily be heavier so it will need to work harder to stay airborne.

Once the lift is cruising at a constant speed everything will weigh the same as normal.

The air in which the fly is flying is held inside the lift and is going up at the same speed as everything else in the lift, so the fly will not need to fly up.

When the lift starts to decelerate, the fly will be momentarily lighter so it won't have to work as hard to stay airborne.

I hope this answers your question.
Cheers.

Answer 4

The air will not lift the fly. The air will flow around it and compress in regions. This is elementary fluid dynamics.

And yes, the fly would have to fly to rise with the lift, otherwise the floor below would collide with it.

Answer 5

Only slightly due to the fly's inertia. The fly will move with the air in the elevator. The air also compresses a bit, with the air density slightly higher in the bottom of the elevator. Therefore the fly must move up a bit to maintain its position relative to the elevator car.

Hope this helps!

Answer 6

Not if it doesn't want to but if it does it will fly normally because the air in the lift is moving upward as is the fly.

Answer 7

no because the air goes up as well.

its the same principle as a moving bus, if you jumped you wouldnt go backwards, unless you was on a open top and the air pushed yopu back slighly

or same principle as the earth spinning, it spins at a 1000mph, doesnt mean flys gotta fly 1000mph just to stay still

same principal as earth going around the sun.........................

sure you get the picture.

(I had a massive argument with friends about this, it was funny though)

hope that helps/

Answer 8

Fly's the same as you Chris - you don't have to jump up when you're going up in a lift, do you?

Answer 9

If you jump in a train you move with the train so I presume that the fly doesn't have to fly up. I couldn't tell you why though.

Answer 10

Why would it need to fly?
It would just cling to a surface and arrive higher up, the same way you would do.