Passengers in Sudden Plane Vertical Drop: Effects

[ellieee]

Homework Statement

exact qn:
when airplane suddenly drops down Vertically, why do people hit the ceiling of the airplane?
is it something about inertia? but I was also thinking about newton's third law. when plane drops down(force is downwards), then I go upwards cuz it's the opposite force?

Relevant Equations

nil

nil

 

[haruspex]

is it something about inertia?

Yes.

but I was also thinking about Newton's third law. when plane drops down(force is downwards), then I go upwards because it's the opposite force?

Please quote that law, then check whether it fits this circumstance.

 

[ellieee]

may I know the explanation?

Yes

 

[haruspex]

may I know the explanation?

We don't do your homework for you. Please show some reasoning.
What forces act on a passenger?

 

[ellieee]

We don't do your homework for you. Please show some reasoning.
What forces act on a passenger?

gravitational force

 

[haruspex]

gravitational force

Before or after the plane drops suddenly?

 

[Delta2]

don't we need to know if the plane falls down with acceleration less, equal or greater than g?

 

[haruspex]

don't we need to know if the plane falls down with acceleration less, equal or greater than g?

I was hoping to get @ellieee to discover that.

 

[ellieee]

Before or after the plane drops suddenly?

is it both? I think it's because when you're not moving, gravitational force will still act on you.

 

[ellieee]

don't we need to know if the plane falls down with acceleration less, equal or greater than g?

but the question didn't state the value of the acceleration of the plane

 

[Delta2]

but the question didn't state the value of the acceleration of the plane

Ok then its up to you to take the cases $a<g,a=g,a>g$. From what I can understand in the first two cases the passengers won't hit the ceiling...

 

[rsk]

but the question didn't state the value of the acceleration of the plane

Usually (maybe even always) if a questions says 'drop' it means under gravity, so the acceleration is the acceleration due to gravity, unless you're given info regarding other forces such air resistance, which you're not in the case.

I can't imagine a situation where a place falls with an acceleration greater than g which doesn't involve Bond like baddies with huge magnets somewhere.

 

[ellieee]

acceleration is the acceleration due to gravity

but isn't gravitational force always acting on the plane? shouldn't the value of the acceleration be greater than acceleration due to gravity ?

 

[haruspex]

but isn't gravitational force always acting on the plane?

Yes, but it is not the only force on the plane.

I can't imagine a situation where a place falls with an acceleration greater than g which doesn't involve Bond like baddies with huge magnets somewhere.

I can.

 

[ellieee]

Yes, but it is not the only force on the plane.

I can.

there's also lift;upward acting force, thrust; the forward acting force; and drag, the wind resistance

 

[haruspex]

there's also lift;upward acting force, thrust; the forward acting force; and drag, the wind resistance

Good, but how could the sum of those result in the plane accelerating downward faster than g?

 

[ellieee]

Good, but how could the sum of those result in the plane accelerating downward faster than g?

the lift force decreases ?

 

[haruspex]

the lift force decreases ?

Could that lead to a downward acceleration faster than g?

 

[ellieee]

Could that lead to a downward acceleration faster than g?

hmm why not? if lift force decreases, then resultant force would be downwards no?

 

[haruspex]

hmm why not? if lift force decreases, then resultant force would be downwards no?

The vertical forces on a plane are, generally, gravity and lift, roughly in balance. With zero lift, what would the acceleration be?

 

[Shreya]

hmm why not? if lift force decreases, then resultant force would be downwards no?

Lift force is an upward force.
Decrease in an upward force doesn't change gravity

I think in the question we are to assume that the plane is in free fall.
The passengers tend to be in rest due to inertia
And then you know what happens!

 

[haruspex]

Lift force is an upward force.
Decrease in an upward force doesn't change gravity

I think in the question we are to assume that the plane is in free fall.
The passengers tend to be in rest due to inertia
And then you know what happens!

That does not work. The passengers would also be in free fall.

 

[Shreya]

That does not work. The passengers would also be in free fall.

Yes, but they will take some time to get to same velocity as the plane is.

 

[haruspex]

Yes, but they will take some time to get to same velocity as the plane is.

Why?

 

[Shreya]

Why?

I think I got it wrong.
The plane must be experiencing acceleration greater than g (due to turbulence)
If the air pressure above the wings becomes higher (somehow) than the air pressure below the wing.
The lift could act downward.

 

[haruspex]

I think I got it wrong.
The plane must be experiencing acceleration greater than g (due to turbulence)
If the air pressure above the wings becomes higher (somehow) than the air pressure below the wing.
The lift could act downward.

Let's give @ellieee a chance to contribute.