Terraforming Mars

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Random stuff? I just paraphrased what I had just said a minute ago. It was valid enough for you to reply a minute ago and now it is random?
xerzi wrote:
If you were to stand on a scale in an elevator and it started to move really fast upward your weight would be greater.

Yes, but you only feel weightless once the elevator plummets (will be weightless until the elevator hits bottom and kills you).

http://en.wikipedia.org/wiki/Reduced_gravity_aircraft
Correction, force can be caused by gravity, which in my case is acceleration. Weight is the force applied on a mass due to gravitational acceleration(Newton's second law anyone?). Both force (and therefore weight) and acceleration (and therefore gravity) can be vectors as they both hold a magnitude and direction.
This argument breaks down if you decide to talk about the gravitational constant and not acceleration.

You are correct, xerzi, with the elevator situation, as the person's mass would be accelerated more than by the gravitational acceleration, which would make the person appear to weight more.

Weightlessness depends on cancelling out all the forces acting upon the object, and one of the ways involves a plane as someone previously mentioned.
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Random stuff? I just paraphrased what I had just said a minute ago.

You made no mention of less gravity making you lighter in your previous post.

You are correct, xerzi, with the elevator situation, as the person's mass would be accelerated more than by the gravitational acceleration, which would make the person appear to weight more.


Mass != weight.

Weightlessness depends on cancelling out all the forces acting upon the object, and one of the ways involves a plane as someone previously mentioned.


Gravity is still acting on the person though, so not all forces are cancelled.
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By Newton's second law: F = ma (magnitude only)

When did I say mass == weight?
F(due to acceleration of the elevator) = m(person)*a(acceleration from elevator)
F(due to gravity) = m(person)*g(gravitational acceleration)
F(total) = F(due to acceleration of the elevator) + F(due to gravity)
=> F(total) > F(due to gravity)

Result: Person appears to weigh more.



Gravity is still acting on the person though, so not all forces are cancelled.

Gravity is not a force as you imply. There is a force due to gravity, which is usually called weight. The person can accelerate due to gravity, but gravity does not "act" on the person. It is the force due to gravity that is acting on the person.

Also:
Assume the acceleration due to the plane is a and that a equals g, the gravitational acceleration (Never really equal but for the sake of simplicity, let's say they are).
Assume no friction due to air.
Assume the mass of the person does not change.
Assume the plane is ascending.
Therefore:
The magnitudes
F(due to gravity) == F(due to acceleration of the plane)
but the directions are opposite, so the forces oppose each other.
Therefore:
F(total) = - F(due to gravity) + F(due to acceleration of the plane)
F(total) = - m*a + m*g
F(total) = - m*g + m*g
F(total) = 0 N (Newtons)

Result:
Forces have cancelled each other out, and the person experiences weightlessness.

In reality, the forces do not evenly cancel each other out, but the resultant force is low enough in magnitude that the person feels weightless.
Daleth wrote:
Weightlessness depends on cancelling out all the forces acting upon the object
Not necessarily. The weightlessness experienced in space stations and in planes is not due to the cancellation of all the forces acting on an object. Its a situation of free fall. Gravity is still fully acting on the object, (with a force towards the earth). In the plane situation, the plane follows the parabolic trajectory that the free falling person would follow if suddenly the plane didn't exist anymore and the person were just soaring through the air (with no air friction, of course), creating the illusion of weightlessness. There are still forces acting though, just no forces are acting on the object in the frame of reference.
Weight is relative. You can have no weight or plenty of weight in many situations.
You feel weightless in a plummeting elevator for the same reason. The frame of reference is accelerating (and moving along the same path as) the object.
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Thumper wrote:
The frame of reference is accelerating (and moving along the same path as) the object.

Same idea as when you are in a car and stop, your body keeps trying to go forward? Makes me remember the old video I saw in high school physics where they had a gyro in a trailer attached to a snowmobile, fired a flare up and changed speeds, during the constant speed the flare went up and down over the same point in the trailer. Speeding up after firing made it fall behind and slowing down made it fall in front.

But either way, I was wrong. Oh well wasn't the first time and won't be the last either.
Thumper wrote:

Compelling argument


Okay, I concede. In my mechanics course, we only spent half a session on frames of references moving with the object, so I'm used to examining objects at some instance of time.
This video describes everything going on here perfectly:
http://www.youtube.com/watch?v=s-33i2b17nc
@Paoletti301 what does that have to do with anything? I would like to be enlightened please.
@giblit

its my way of saying this discussion has gotten quite silly.

as for the discussion, obviously the space station is under the force of gravity, that is what keeps it there.

the feeling of being weightless is exactly that, a feeling.
Paoletti301 wrote:
the feeling of being weightless is exactly that, a feeling.

What? Being able to float around the cabin of the space station makes it look more than a feeling. Now feeling you are being watched in an empty room, that is just a feeling.
Paoletti301 is half right. Weight is a feeling. But we were never debating that. We were debating the cause of the feeling, which I feel is not silly at all, because the concept holds genuine importance in mechanics.
I thought being in orbit is actually just falling, but never reaching the ground. (Thanks vsause :D)

So why are you guys discussing weightlessness in orbit?
On the original topic, I propose daisies.
@Fredbill30
That is correct. We were discussion weightlessness because it was mentioned that "you feel weightless in the space station because there is very little gravity there", which was incorrect.
You feel weightless because you're in free fall along with your frame of reference, which occurs when orbiting the Earth.

ne555 wrote:
On the original topic, I propose daisies.
Care to elaborate? I'm interrested.
ne555 wrote:
On the original topic, I propose daisies.
XD I like jasmine, mmm such a nice smell, like baked bananas.
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