Possible gravity reduction due to near-orbital speeds?

[(An Original Name)]

I was wondering if you did something like taking a aircraft in KSP up to a significant fraction of orbital velocity, will the force of gravity be reduced accordingly? You wouldn't be in free fall, the wings would be providing limited lift too. Would this cause gravity experienced to lower? Is this even true for real-world physics and that I am completly wrong?

[numerobis]

Gravity isn't reduced, but yes, if your horizontal speed is fast, you orbit. Doesn't matter whether you have wings, rockets, or are a rock.

[UmbralRaptor]

Pretty much. You'd see centrifugal* force almost as strong as gravity so you'd need less lift, and if standing in the aircraft feel less weight.

*KSP aircraft operate in a non-inertial reference frame. I stand by my word choice.

[Vanamonde]

Interesting question. Put the gravity meter sensor on your plane and watching the readings as you gain altitude and speed.

[rpayne88]

Gravity isn't reduced, but yes, if your horizontal speed is fast, you orbit. Doesn't matter whether you have wings, rockets, or are a rock.

Although, at those speeds in the lower atmosphere, drag would likely rip your wings off the fuselage.

Edited July 12, 2013 by rpayne88
extrenous use of the preposition "of"

[Flowz0r]

That's not how gravity works, orbits work because you're going sideways faster than you're falling back to earth, not because there's less gravity further up in the atmosphere.

[rpayne88]

That's not how gravity works, orbits work because you're going sideways faster than you're falling back to earth, not because there's less gravity further up in the atmosphere.

I may be wrong, but I believe you are partially incorrect. True, orbit is "free falling around the Earth (or Kerbin, Mun, whatever,)" but as you increase your altitude farther from the center of mass of the object you are orbiting, the less gravity you will experience (Scott Manly.) But, as said above, this subtle change is not enough to place you in orbit.

[Flowz0r]

I may be wrong, but I believe you are partially incorrect. True, orbit is "free falling around the Earth (or Kerbin, Mun, whatever,)" but as you increase your altitude farther from the center of mass of the object you are orbiting, the less gravity you will experience (Scott Manly.) But, as said above, this subtle change is not enough to place you in orbit.

You're absolutely right. I was trying to say that the change is incredibly small and negligible while you're still traveling inside the atmosphere, which you would have to with a regular plane.

[(An Original Name)]

I know that gravity doesn't decrease THAT fast when you get above a planet's atmosphere and get into space, weightlessness is due to no force but gravity (except when there are minuscule forces like drag or tidal forces acting upon an object, then it is microgravity) acting upon an object, then it is in free fall. I was wondering if the FORCE of gravity was reduced due to the horizontal speed of an object (say an aircraft) that was actively resisting gravity's attempts to move it downwards by using its wings for lift, but it didn't need to use all of its lift capability to keep from falling, as the ground was curving away at a noticeable rate due to speed alone, creating lower levels of gravity due to centrifugal force. At least, I think that's correct

[Pbhead]

Yall have your gravoli detectors, use em!

[Luxmaster-CZ]

Gravity decrease with the power of two of distance from body.

I made a try.

Get up to 20 km, measure gravity. Get significant horizontal speed, measure gravity. (didnt changed)

slowly increase height, got AP to 150 km. Drift there and measure gravity every 10 km.

http://imgur.com/a/MsgrD

here is album

: Gravity does not change with orbital speed, only with distance from body.

Acceleration, however, does change to zero when reached orbit

Edited July 12, 2013 by Luxmaster-CZ

[Grizzlol]

The Gravoli instrument is not affected by forces other than gravity, as opposed to the G-force indicator, which is the main difference between the two. The change in gravitational force at higher altitudes is not massive but it is not at all insignificant. There is a measurable difference within just a few thousand meters of altitude. In orbit, the G-force indicator will read zero because gravity is pulling on all atoms equally, while the Gravoli instrument will read less than what it does on the surface because the gravitational pull depends on the distance to the body. In addition, your TWR is directly related to the value given by the Gravoli instrument.

Edited July 12, 2013 by Grizzlol

[Fr3Runn3r]

Gravity is completely unaffected by horizontal motion. F=GMm/(r^2) this is the formula for the force due to gravity and as you can see it depends only on the masses of the two objects and the distance between them (G is the gravitational contant). The confusion here is being caused by the lift. If we take the plane as our reference point and look at the forces acting on it we will see gravity acting downwards and lift acting upwards (and drag acting against the motion, but we can ignore that for this argument). No matter what the horizontal speed of the plane gravity will remain the same, the only force that will change is the lift. Now the acceleration is calculated by F=ma where F is the SUM of the forces acting on the object, so since gravity and lift are acting in opposite directions when they are summed the result is less than what we would have with gravity alone. Therefor the acceleration is less. However I will stress this again the gravity is not changing, nor is the acceleration due to gravity. The only thing that changes is the total force and the total acceleration.

Also can people in this thread please stop talking about centrifugal force, it does not exist. Hope this helps.

[Grizzlol]

Also can people in this thread please stop talking about centrifugal force, it does not exist. Hope this helps.

I would not be the only one reacting to "it does not exist". It may be that it is just a concept, an apparent effect caused by inertia and in that sense it is not actually a force, and it would be negligible in a regular plane, but I do not see a reason to disregard it as the title of the thread is "...near-orbital speeds".

The actual gravitational force does not change with horizontal speed, but the perception of it does due to the centrifugal force (inertia). How is this wrong?

Edited July 12, 2013 by Grizzlol

[lazarus1024]

I know that gravity doesn't decrease THAT fast when you get above a planet's atmosphere and get into space, weightlessness is due to no force but gravity (except when there are minuscule forces like drag or tidal forces acting upon an object, then it is microgravity) acting upon an object, then it is in free fall. I was wondering if the FORCE of gravity was reduced due to the horizontal speed of an object (say an aircraft) that was actively resisting gravity's attempts to move it downwards by using its wings for lift, but it didn't need to use all of its lift capability to keep from falling, as the ground was curving away at a noticeable rate due to speed alone, creating lower levels of gravity due to centrifugal force. At least, I think that's correct

No, the gravity experience is the same. An object in low Earth orbit is experience a relatively similar amount of gravity to one sitting on the surface, and that is at full orbital speeds. However, as you move faster over the surface of the earth the EFFECT is that gravity SEEMS reduced the faster you go, as your forward velocity curves your trajectory partially around the center of the Earth.

Frame of reference gravity is reduced, however, force of gravity does not change (not entirely true as at 300km or so altitude I think the force of gravity is something roughly like 90% that of sitting on the surface due to the extra distance from the Earth)

[lazarus1024]

I would not be the only one reacting to "it does not exist". It may be that it is just a concept, an apparent effect caused by inertia and in that sense it is not actually a force, and it would be negligible in a regular plane, but I do not see a reason to disregard it as the title of the thread is "...near-orbital speeds". No, the actual gravitational force does not change with horizontal speed, but the perception of it does due to the centrifugal force (inertia). How is this wrong?

It is wrong because there is NO such thing as centrifugal force, it is centripetal force you mean. Centripetal is "center seeking", centrifugal is "center fleeing".

A centripetal force acts to keep and object moving around a center point. In the case of an orbit, gravity is acting as a centripetal force to keep the object orbiting the center. A car moving around a turn, the tires are exerting a centripetal force on the ground through static (or if sliding around the turn, dynamic) friction to push the car around the turn.

Centrifugal "force" isn't really a thing. Centrifugal force is the movement away from the center point and is a lack of centripetal force. It isn't a force at all. Centrifugal "force" is what you feel being shoved to the outside of your car as you go around a turn. No force, it is simple inertia attempting to keep you going in a straight line, but the centripetal force of the tires are pushing the car around the turn and in turn the centripetal force of your seat, seatbelt, "Oh S*$& handle", etc are pushing you around the turn as well, so that inertia does not allow you to continue moving in a straight line.

Basic high school physics (which either a lot of people don't take anymore, or don't remember/sleep through).

Centripetal force = a thing

Centrifugal force = not a thing at all. Inertia

[Grizzlol]

I do know basic physics. You are pointing out that the gravity is acting as a centripetal force and is the only thing that is an actual force, I was pointing out that centrifugal force (inertia) is what counters the gravity as the object curves around the surface (as it wants to continue forward) and as such causes the perception that gravity is no longer there due to being in a constant free-fall.

Edited July 12, 2013 by Grizzlol

[lazarus1024]

My point is that centrifugal force doesn't exist. Centripetal force is generated by gravity acting at a perpendicular to the forward velocity of the object. Thus a curved path occurs and when centripetal force reaches equillibrium with the forward velocity of the object a circular orbit occurs.

I am saying centrifugal force doesn't exist at all. Inertia is not a force.

To clarify, calling inertia a force would be like calling a car a spaceship. It isn't a spaceship, it is a car. Worse is calling inertia resulting in an object moving in a curved path that is having a centripetal force acting on it, "centrifugal force" is like calling a car the NCC-1701 Enterprise.

It isn't a spaceship and it especially isn't the Enterprise. It is just a car (IE Inertia). You wouldn't say that mass is a force, or that a gallon of milk is a force. Inertia isn't a force and "centrifugal force" is just a layer on top of that. At best you might be semi-sort of accurate to say something like centrifugal inertia.

Edited July 12, 2013 by lazarus1024

[Fr3Runn3r]

The actual gravitational force does not change with horizontal speed, but the perception of it does due to the centrifugal force (inertia). How is this wrong?

Take out the words centrifugal force and it's not wrong. However the name of this tread is suggesting that the value of the gravitation force is changing "Possible gravity reduction due to..." I therefor stand by what I have said as I'm simply applying A-level physics/maths.

PS. Thanks for defending me lazarus1024

[Grizzlol]

I never said inertia is a force. I was referring to the term, which most assuredly does exist, "centrifugal force" as is, whether or not it is a force, nor did I intend to imply that inertia is responsible for an object moving in a curved path (which would indeed be the centripetal force), but the contrary (resisting change in movement).

Moreover, I never implied that you were wrong about anything, I just did not like your original statement "centrifugal force does not exist", without any clarification whatsoever, but now we do have a very detailed clarification, thanks.

I will say, though, that centripetal force is much less commonly known, and in this case it is indeed the centripetal force (simply the gravity) responsible for the resulting orbit, not centrifugal force.

Edited July 12, 2013 by Grizzlol

[wolfedg]

Is this what you are looking for?

[(An Original Name)]

Maybe I made a little mistake with the title... I meant that does the PERCEPTION of gravity change as an object approaches orbital speeds? I know that the strength of gravity stays the same, but inertia cancels out part of the FORCE of gravity, not the actual gravity fields strength, that an object is experiencing.

[OtherDalfite]

Is this what you are looking for?

That's not quite the same thing really. The Vomit Comet works by going high up, and then pitching down for a while, giving episodes of low gravity. This can simulate the Moon's, Mars', or zero-g. It's also used in films.

[Cartz]

That's not quite the same thing really. The Vomit Comet works by going high up, and then pitching down for a while, giving episodes of low gravity. This can simulate the Moon's, Mars', or zero-g. It's also used in films.

It's EXACTLY the same thing, just, the vomit comet does not have enough horizontal velocity to miss the ground. Orbit is literally a free fall with enough sideways motion to constantly miss the earth. The comet can do the freefall bit, just not the missing the earth bit.

To the OP, who just posted a follow-up, its an interesting point that I hadn't considered before. But I'd have to assume that yes, as you approach orbital velocities that your inertia would being to alter your perception of gravity.

Seeing as the null hypothesis would postulate a 'normal' gravitational experience until orbital velocity was achieved, at which time weightlessness is experienced instantaneously, one has to assume there is some sort of gradual introduction to weightlessness. I have no idea what that curve looks like, and I have even no desire to math it out.

[OtherDalfite]

It's EXACTLY the same thing, just, the vomit comet does not have enough horizontal velocity to miss the ground. Orbit is literally a free fall with enough sideways motion to constantly miss the earth. The comet can do the freefall bit, just not the missing the earth bit.

To the OP, who just posted a follow-up, its an interesting point that I hadn't considered before. But I'd have to assume that yes, as you approach orbital velocities that your inertia would being to alter your perception of gravity.

Seeing as the null hypothesis would postulate a 'normal' gravitational experience until orbital velocity was achieved, at which time weightlessness is experienced instantaneously, one has to assume there is some sort of gradual introduction to weightlessness. I have no idea what that curve looks like, and I have even no desire to math it out.

While it may be the same zero-g. What they are doing to get it is different. What OP implies is going fast enough in an aircraft to cancel out gravity due to very high speeds near orbital velocities. The vomit comet simply dives downward, not accelerate to high speeds.