Force of Gravity and G’s are two different things!

G is the estimated acceleration an object will experience at sealevel neglecting air resistence [9.81 m/s^2]. This is not a force! This is a rate of acceleration. You will find that objects will experience this approximate acceleration when they initially begin freefall. This is because air resistance is negligable at low velocities. Eventually the object will reach terminal velocity and stop accelerating. By definition terminal velocity means no more acceleration. Thus 0 G’s

Just remember gravity exerts forces onto objects. This force is constant(@sealevel) regardless of motion. G is the estimated acceleration for freefalling objects. Lets calculate how many G’s a driver experiences accelerating down the road.
0 to 60 mph, 2.8s
[vf=vi+a*t]
vi=0mph=0m/s
vf=60mph=26.82m/s
t=2.8s

vf=vi+a*t, 26.82=0+a(2.8), a=9.58m/s

G=a/9.81, G=9.58/9.81, G=.98

This cars average rate of accelearation is approx. 1 G when accelerating from 0 to 60. Long story short if your driving this car your going to experience an acceleration similar to one you would experience if you jumped off a cliff. Sweet

My understanding of General Relativity is somewhat limited, (the math is tremendously more advanced than in Special Relativity, and was hard to follow…I was taking a 3rd year Physics course with limited math skills) but thought experiments led Einstein to equate gravitational force to acceleration. After all, if you stand on a scale in an elevator, your weight changes when you’re accelerating or decelerating. He thought that gravitation and acceleration might stem from the same phenomenon. So he did the math for it.

What ended up happening was, he ended up combining the 3 dimensions of space with the 4th dimension of time, and they turn out to be interconnected. Energy and mass distort space-time, and create “dimples” in this 4-dimensional space. I won’t mention any equations or mathematics because it would take untold pages and I dunno if anyone could follow. I probably can’t anymore. But needless to say, all of the classical formulas go out the window. And mg is NOT the force of gravity. It is only an approximate description of how objects behave due to the phenomenon of gravity on earth. If you take a look at GR, you’ll see that gravity is actually not a force at all, but just the natural movement of objects in 4-dimensional space-time. When a satellite orbits the Earth, there is NO force pulling it towards the Earth to keep it moving in a circle. It’s simply following a straight line in 4-dimensional space-time, which in 3 dimensions we pereive as an ellipse. You can look on the internet if interested, but there’s simple comparisons you can do going from 2 dimensions to 3 dimensions, where movements have weird translations when adding/removing a dimension.

So, when you jump out of a plane, or you’re in space, what happens is that your body returns to its natural trajectory in 4-dimensional space time, and you’re actually not getting pulled by the Earth by some magical force “mg”. (which is wrong…you can find the real equations for gravitation in many textbooks) What happens when you’re on the Earth is that the Earth is pushing you up and accelerating you away from what would be your natural trajectory in 4 dimensional space time. So when you jump out of a plane, there is actually no force pulling you down at all. What’s happening is that due to a lack of force pushing you up, you being to resume your natural trajectory.

I haven’t read this page so I haven’t checked it for correctness, but I trust Wikipedia to explain GR correctly in layman’s terms…I hope.

So if you want to do some reading, here you go…if you want to see the proof, I hope your math skills are stunning, and you can consult a higher level Uni textbook…

http://en.wikipedia.org/wiki/General_Relativity#Treatment_of_gravitation

here’s the rundown:

story about a fun car mag
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specs in
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unobtainable car sets new std for a real car
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semantic comment
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11th grade physics
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einstein says blah blah…. (no discernable point)
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someone who probably knows what they’re talking about throws fuel on the fire without making an attempt to point out that the topic argued isn’t the topic of interest in the thread… not you Kinno…
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guy who loves car news way too much for his own well-being provides run down for anyone skimming along to see how this all pans out.

Accelerating directly towards a gravitational source FEELS completely different than when accelerating perpendicular to it. If you accelerate at 1 G towards the G source, you feel weightless. That’s how the so-called Vomit Comet jet can replicate the sensation of being in space, whereas when accelerating in a hard charging Veyron, your ass gets pressed hard against the seat. Completely different sensations.

Doing the math of acceleration vectors (ie, direction and magnitude) makes it clear.

Could the Veyron beat a Ferrari F1 ? Probably not. Silly to pit it against an Atom to me.

Oh yeah – good one BAMF.

It’s 9.81m/s2 folks. If you use 10, I’ll count it WRONG. No partial credit. For those insisting on using “irrational” English units, 32.17ft/s2 will be accepted.

Carsfeverguy, not to worry. What Kinno is talking about will NOT be on the test. Meditate on the pearls I’ve put before you, think about the acceleration of the Veyron, and all of this will drop into place for you. We will be talking about Albert and his pals next semester.

Oh, and don’t forget your homework tomorrow!!

Kinno, no offense to you, but you didn’t say a single thing about our beef with Que.

BTW, if you need to reach beyond classical physics to explain something like this, then ya’ll should have other careers.

Ok, good afternoon, good evening, good night. I’ve wasted enough spit on this. Que, go jump out of a plane, with or without a parachute, and let us know ok?

Ciao everybody

Albert Einstein, like the guy without whom nuclear energy would never have existed. Oh yeah, did I mention that computers (and all things that use them…which is like everything electrical invented in the last half a century…) wouldn’t exist without his theories? Neither would satellite communication, nor would it have been possible to fly to the moon. Yep, Einstein, the father of not only virtually all modern physics, but most things using modern technology in existence.

He came up with a WHOLE lot of ****. The particular **** that comes into play here is General Relativity. It explains what gravity actually is, and not what Newton thought (or didn’t think, actually…he had no explanation for what gravity actually was) it was. After coming up with his theory, and his formulas, they were tested against Newton’s formulas by measuring the orbit of … Pluto I believe. Guess whose equations turned out to be right?

Anyways, I don’t have enough space here to explain, but I’ll try if someone asks. Just this though…when you jump out of a plane, for the first instant, you’re experiencing the same thing as what Astronauts experience in space: freefall. Contrary to what Newton would have you believe, when you’re in freefall the Earth is NOT pulling on you at all. When you’re standing on the ground, the Earth is not pulling you down, it’s pushing you up. If you remove the Earth and it stops holding you up, you go down.

I know that’s not an explanation, but an explanation of General Relativity requires … well I won’t try. It’s damned difficult to understand, having it explained by a Physics professor. How Einstein ever managed to figure that out is beyond me…

Your persistance will not stop to amaze me. Go ask one of your teachers.. since it seems you’re still in school.

(proof you’re still in school? 9.81… the .01 actually changes well within our atmosphere, but either way it’s so irrelevant. The fact that you stress 9.81 means that you’ve just learned this the other day (obviously haven’t mastered it quite yet).)

P.S. My university professor used to use 10 as the force of gravity, because the calculations are not as relevant as knowing what you’re doing.

I’ll use small words so you’ll be sure to understand. Perhaps you will finally be able to connect the dots. When you accelerate at 9.81m/s2 straight down, the sensation you feel is weightlessness, like floating in space. When you are sitting in a car on the ground, your ass is pushing down on the seat with a force of 1G times your mass, even though you are not accelerating. If a car can accelerate forward at 1G, then you ass and your back feel 1G of force each, because you are accelerating 90 degrees from gravity in one plane and being pulled down by gravity in another, even though you are not moving relative to that plane. This starting to make sense?

Now, back to the freefall; once you stop accelerating downward (but reach some constant velocity), you feel the force of gravity again, 1G times your weight. If a plane goes into a dive, you feel weightless ONLY IF IT IS ACCELERATING DOWN AT 9.81m/s2. If it is in a dive, but reaches a constant velocity, you feel your full weight again. Ke, you listening to this?

Homework is due tomorrow, and if this still doesn’t make sense, perhaps you are in the wrong class.

HOWEVER, I’m sorry Que, but go back to the books (and also stop speaking like you’re some monarch you !@#$)

When in doubt: go back to the formulas.

F=ma Right? If speed is constant, then a=0, then F=0!! (net force that is) So I do believe the feeling of weightlessness comes in once you reach terminal velocity and feel NO net forces (NOT like on the ground). And while you jump out of the plane then you certainly will feel an acceleration (and NOT weightless), like as if you threw yourself off a building (please do so before you say ‘que has spoken’ again).

Ok?

Now get all back to work, or go spend your time otherwise people.

What grade are you guys in, anyway?

Ke and Scott, you listening to this? If you’re not careful, you just might learn something.