freefall (1 Viewer)

[doodydo]

is an object in freefall on earth in an inertial frame of reference?

 

[...]

woah, its accerlerating towards the centre of the earth...

 

[tooheyz]

Originally posted by ...
woah, its accerlerating towards the centre of the earth...

so its a non inertial frame of reference...

 

[Xayma]

Until it reaches terminal velocity. Where it is no longer accelerating...

 

[KeypadSDM]

Originally posted by Xayma
Until it reaches terminal velocity. Where it is no longer accelerating...

Well technically ...

If you're on the surface of the earth, you're in a non-inertial frame of reference... Hence if you're falling to 1 section of the ground on earth at a constant velocity, you're still accelerating.

Pedanticism aside, yes you're right.

 

[Constip8edSkunk]

if you putted that way, there are no inertial frames of reference, it being an idealism just like perfect circles squares etc....

 

[KeypadSDM]

Originally posted by Constip8edSkunk
if you putted that way, there are no inertial frames of reference, it being an idealism just like perfect circles squares etc....

Very true. Every object exerts the force of gravity on us, hence there can be no place free from all forces, and hence no inertial frames of reference.

Or at least very hard. You'd have to do some pretty freakin massive calculations to figure out the exact acceleration required in the right direction to be in an inertial frame of reference...

 

[CHUDYMASTER]

Gravitational forces are infinite in their expanse, as are all the other known forces. Hence it is IMPOSSIBLE to be in a perfect inertial frame of reference...if such a thing can be said...

 

[zeropoint]

Originally posted by tooheyz
so its a non inertial frame of reference...

Quite the opposite; a freely falling object devoid of any non-gravitational forces exists in a locally inertial frame. In fact, an object at terminal velocity or on the surface of the Earth is non-inertial.

 

[CHUDYMASTER]

What exactly do you mean by "locally inertial frame"??? Never heard of that before...

 

[zeropoint]

The frame is locally inertial in the sense that the gravitational field strength is non-uniform and hence changes with altitude.

 

[CHUDYMASTER]

but gravitational field strength varies inversely with altitude...And even then, I fail to recognise your argument.

 

[zeropoint]

Originally posted by CHUDYMASTER
but gravitational field strength varies inversely with altitude...And even then, I fail to recognise your argument.

Yes. That's why I called it a ``locally inertial'' frame. The object would be purely inertial in a uniform (non-existent) gravitational field.

Please note that the confusion arises from the fact that Special Relativity considers only a flat Minkowski space-time free of mass and gravity. In such cases, we must employ General Relativity in which space-time is deformed by the presence of mass and energy. This is of course significantly beyond the scope of the HSC syllabus, and as such the question posed by the original poster is very vague indeed.

 

[doodydo]

ok- I'll give the original question

identify if in an inertial or non-inertial frame of reference:
standing enclosed in a lift in which the cable has snapped

 

[...]

thats non-inertial..

inertial would be just sitting in a train where it is travelling at a constant velocity

 

[tooheyz]

yeah inertial frame is one where ur travelling at constant speed or at rest. if ur accelerating then its non-inertial.

i never heard of the 'local' stuff ur talking about..

 

[zeropoint]

Originally posted by doodydo
ok- I'll give the original question

identify if in an inertial or non-inertial frame of reference:
standing enclosed in a lift in which the cable has snapped

Let person A be enclosed in a lift undergoing free fall. Let person B float in space far away from any mass. There is no experiment that can be performed to distinguish between the frames of A and B. Hence A is inertial.

 

[KeypadSDM]

Originally posted by zeropoint
Let person A be enclosed in a lift undergoing free fall. Let person B float in space far away from any mass. There is no experiment that can be performed to distinguish between the frames of A and B. Hence A is inertial.

They could both be non-inertial frames of reference.

 

[zeropoint]

Originally posted by KeypadSDM
They could both be non-inertial frames of reference.

No. They could not.

 

[xiao1985]

Originally posted by zeropoint
Let person A be enclosed in a lift undergoing free fall. Let person B float in space far away from any mass. There is no experiment that can be performed to distinguish between the frames of A and B. Hence A is inertial.

careful... alil bit of extra infomation is disastrous... =)

edit: i fink as far as hsc is concerned, yes s/he is in non-inertial frame of reference.

but accordin to this, den every frame can be considered as inertial usin the same arguement??