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# A speed beyond light question ^^

1
Wed 5 Apr, 2006 06:58 pm
I think E confused the issue by mixing the terms speed with velocity. Velocity has a vector or directional component. The earth is accelerating because its direction changes as it orbits the earth but its speed (or angular velocity) is constant ie it takes about 365 days to do a 360 degree lap of the sun.

At the summer solstice (SS) it is travelling in the opposite direction to that which it travels at the winter solstice (WS). If it's velocity at SS is X then it's velocity at WS is -X and that is a change in velocity which means, in physics terms, the earth is accelerating - but it's speed doesn't increase.
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1
Wed 5 Apr, 2006 07:03 pm
Spendy's when do we get flung off the planet is more about the oppositional forces involved on the Earth itself ie gravity (caused by the mass of the earth) vs centrifigal force caused by the earth spinning on it's access.

Do we weigh more or less when the part of the earth we're standing on is not facing the sun? ie is the centrifigal force created by the earth orbiting the sun greater than the gravitational attraction of the sun?
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ebrown p

1
Wed 5 Apr, 2006 07:50 pm
spendius wrote:
I must say,at this point,that I wasn't trying to unleash all this comical banter.

What I was wondering,scientifically, was that if the earth was accelerating,as E said it was,how long will it take before centrifugal forces chuck us all off into orbit or even further.Will fatties be "selected in" by dint of them lasting longest and,logically,should I try getting fat by gorging on all my favourite gobdribblers.

Spendius,

I am not sure if I should be offended (I am actually quite difficult to offend), but everything I have said in this post is scientifically correct and backed up with a Physics degree if it matters.Truthfully I don't really care if you accept what I am saying or not, I am writing this for the intellectually curious, not the cynically dismissive.

The thought experiment I offer is an interesting one.

To answer your question, the earth is accelerating as I suggest. The acceleration is very slight, You don't need to worry about being thrown off for several reasons, one of which is that you are rotating around the Sun at the same rate as the sun, which means that you have practically the same acceleration as the earth.

Also, if it matters (meaning if you aren't too cynical for this to interest you) how fat you are doesn't matter. The equations for acceleration have nothing to do with mass and so a fly will have the same acceleration due to a circular motion as an elephant.

Why do I waste so much time answering cynicism?
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ebrown p

1
Wed 5 Apr, 2006 07:52 pm
hingehead, I am trying to simplify a thought experiment to provide an introduction to Galiean relativity without needing to address vector math.

I thought I handled that adequately by using speed, and talking about the value (by this I mean the absolute value) of acceleration).

I think my train thought experiement is a valuable one. How would you make it clearer?
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1
Wed 5 Apr, 2006 09:42 pm
E - I wasn't even considering your thought experiment, I was replying to Spendy's question.
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spendius

1
Thu 6 Apr, 2006 06:52 am
E wrote-

Quote:
Why do I waste so much time answering cynicism?

Perhaps you might like doing.

But there was a serious question in what I said. My flippant style shouldn't disguise that.

At what rate are we accelerating and what period of time is required for that particular factor to render life impossible?
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Steve 41oo

1
Thu 6 Apr, 2006 07:54 am
When a force acts on a body it produces an acceleration. In this case the force is the suns gravity acting on the earth. The earth accelerates towards the sun, but as its already moving, it "falls" in a circular path which is the earth's orbit. I just thought of something though. During the day at the equator when the sun is overhead the gravitational forces of the earth and the sun are in opposite directions. But at night they are in the same direction. Therefore (in equatorial regions at least) people weigh more at night. Is this correct?
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ebrown p

1
Thu 6 Apr, 2006 09:32 am
Spendius, and Steve.

What you are missing is that You are orbitting around the Sun. If the Earth magically disappeared and left you, with nothing but a space suit, you would orbit around the sun in almost exactly the same orbit the Earth takes.

Without the earth. You would go around once every 365.25 days.

Weight is the force of Earths gravity pulling you toward the center of the Earth. So by definition the speed of the Earth around the Sun will not effect your weight at all.

But furthermore we measure weight by standing on a scale. Since the earth and the scale and you are all orbitting the sun, the scale will read the same whether you are facing the sun, or away from the sun, or sideways. Here's another image, imagine what the scale would read if you taped in to your feet as you were orbitting the Sun (without any Earth to pull on you).

To answer spendius' question, the acceleration would have to be very high... as I said our acceleration due to the Gravity of the Sun is very slight.
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ebrown p

1
Thu 6 Apr, 2006 09:34 am
Here are two interesting questions to ponder. If you can answer these questions in a way that doesn't contradict, you probably understand what I am trying to explain.

1) What keeps the Moon Orbitting around the Earth (instead of drifting out into space)?

2) Why are the people in the Space Shuttle orbitting around the Earth (much closer than the Moon) weightless (i.e. they float around with no effect of gravity)?
Steve 41oo

1
Thu 6 Apr, 2006 10:14 am
ebrown_p wrote:
Spendius, and Steve. What you are missing is that You are orbitting around the Sun.
I've always thought Spendius was orbiting around the sun, but I'm not

Sorry ebrown but your answer does not satisfy my point about weighing more at night. Weight is a product of mass and acceleration. Acceleration being a vector quantity can be added or subracted according to its direction. And the direction of pull of the sun's gravity changes with respect to that of the earth for an earthbound observer because of the earth's rotation. It has nothing to do with the earth orbiting around the sun. Similar considerations with respect to the earth moon (and sun) gravitational forces account for the tides.

I accept btw that the effect is small and could not be detected by a scale balance, as both sides would be equally affected, but it could be detected by a sensitive enough spring balance.
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ebrown p

1
Thu 6 Apr, 2006 10:25 am
Steve (as 41oo) wrote:
I accept btw that the effect is small and could not be detected by a scale balance, as both sides would be equally affected, but it could be detected by a sensitive enough spring balance.

Steve, The effect is exactly zero.

Answer this question if you want to continue to argue this point.

Why are the astronauts orbitting the Earth in the Space Shuttle weightless?
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Steve 41oo

1
Thu 6 Apr, 2006 10:30 am
They are not weightless. Why do you think its termed micro-gravity?
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ebrown p

1
Thu 6 Apr, 2006 10:42 am
You are splitting hairs. Answer this question then:

Why do they float around in "micro-gravity" (i.e. insignificant amounts of acceleration).

(Incidently the reason there is "micro-gravity" instead of zero gravity is that there are other slight forces on the shuttle such as residual friction and perhaps rotation of the ship itself. This is irrelevent to our current discussion).
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Steve 41oo

1
Thu 6 Apr, 2006 11:06 am
I know exactly why they appear to be weightless. But if it takes an answer to get an answer...the shuttle and all on board are following parallel trajectories as they fall through the vacuum of space. My question had nothing to do with orbiting masses but with spinning or rotating masses, specifically the rotation of the earth with respect to the sun. How else do you account for tidal forces?
ebrown p

1
Thu 6 Apr, 2006 11:15 am
The Physics of the Earth orbiting the Sun (with you on it) are the same as that of the Space Shuttle orbitting the Earth.

The gravity of the Earth has no effect on the astronauts because they are orbitting, inside the Space Shuttle, around the earth in the same orbit as the shuttle around them. Their position relative to the Earth doesn't affect the forces on them.

Likewise the gravity of the Sun has no effect on us because we are orbitting, on the Earth, around the Sun in the same orbit as the Earth we are upon. Our position relative to the Sun doesn't affect the forces on us.

BTW. This is classical physics (i.e. that of Newton and Galileo before Einstein). General Relativity has a much more abstract and complex analysis. However it gives the exact same answer. Whether you are pointing toward, or away from the sun has no effect.
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spendius

1
Thu 6 Apr, 2006 12:06 pm
E wrote-

Quote:
1) What keeps the Moon Orbitting around the Earth (instead of drifting out into space)?

2) Why are the people in the Space Shuttle orbitting around the Earth (much closer than the Moon) weightless (i.e. they float around with no effect of gravity)?

Isn't the answer to both a balance of gravitational force or centrifugal and centripetal forces.

If,as you posit,everything disappeared except me,perish the thought,would I move to a position where the centre of the earth is or would my journey around the sun continue to be in loops of radii 8,000 miles.

Do gravitational forces within and without our galaxy affect these things measurably.

Are we in the realms of what Intelligent Design calls "irreducible complexity" and thus invents God to prevent us going off our heads or,to put it another way,prevent us spending too much on scientific research?
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Steve 41oo

1
Thu 6 Apr, 2006 12:18 pm
ebrown_p wrote:
Our position relative to the Sun doesn't affect the forces on us.
Well that cant be true as we all know the gravitational attraction is proportional to the product of the masses and the inverse square of the distance.

Quote:
BTW. This is classical physics (i.e. that of Newton and Galileo before Einstein). General Relativity has a much more abstract and complex analysis. However it gives the exact same answer. Whether you are pointing toward, or away from the sun has no effect.
I thought Einstein was able to refine classical Newtonian physics by accounting for small but observable differences. Therefore the answer would not be exactly the same given a Einstinian as opposed to Newtonian analysis.Supposing you take three masses and line them up A B C. Suppose A is by far the most massive, C next with B of relatively insignificant mass. There will be a force pulling B to A and a lesser force pulling B to C. The net force is deduced by subtraction. Now arrange them A C B. The net force on B is the addition of the AB and CB forces. Agree?
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ebrown p

1
Thu 6 Apr, 2006 12:25 pm
Quote:

Isn't the answer to both a balance of gravitational force or centrifugal and centripetal forces.

No. Gravity is the centripetal force. Centrifugal "force" isn't a real force at all, it is really just momentum. It ceratinly doesn't counter gravity.

Gravity is the sole unbalanced force which is why an object in orbit is accelerating.

Quote:

Are we in the realms of what Intelligent Design calls "irreducible complexity" and thus invents God to prevent us going off our heads or,to put it another way,prevent us spending too much on scientific research?

<<SIGH>> This has absolutely nothing to do with Intelligent Design, which is a religious objection to evolution.

The fact is that science, Physics to be exact, can exactly, precisely and mathematically predict and explain the behavior of objects in orbit. All of the Physics I have given you can easily be confirmed with experiments and these experiments have been done.

The victory of Physics was when Newton's laws (which is what we are discussing now) were found to explain both the behavior of objects on earth and the orbits observed in the solar system.

The science is sound and backed with observation.

If this is a blind religious attack on science, I am leaving.

Is there anyone here who is interested in the Physics. If not, then I quit.
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spendius

1
Thu 6 Apr, 2006 12:27 pm
E-

What about that weightless effect in high flying aircraft in certain trajectories where astronauts practice?
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spendius

1
Thu 6 Apr, 2006 12:36 pm
E wrote-

Quote:
If this is a blind religious attack on science, I am leaving.

Not at all.I was only being curious.I'm not religious.
I was asking about gravity in and beyond the galaxy.Is any of that measureable.I was only wondering about irreducible complexity.
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