JohnMitchell 14
You're mixing your apples and oranges scientifically. Weight is measure of mass in a gravitational field. Vacuum is the absence of atmosphere. People often confuse those points because they equate weightlessness with being in orbit around the Earth. According to your logic, the astronauts would have been weightless on the moon, not just much lighter. An object in an evacuated bell jar on Earth would drift around weightlessly, mindless of the gravity affecting every other object on the planet.QuoteIn vacuum, weight is irrelevant, only mass is relevant. Weight is the function of gravitational acceleration between two objects.
As usual, Happythoughts logic was impeccable.
JohnMitchell 14
I believe that if you started 100,000 miles out or so you'd be close to escape velocity http://en.wikipedia.org/wiki/Escape_velocity when you hit. For Earth, that's about 25,000 mph. Some of the really smart math pros here could figure it out exactly.QuoteYes, in a vacuum, you'd continue to accelerate with no drag. You'd be going like 1,000 mph (a guess) when you hit the ground.
QuoteI believe that if you started 100,000 miles out or so you'd be close to escape velocity http://en.wikipedia.org/wiki/Escape_velocity when you hit. For Earth, that's about 25,000 mph. Some of the really smart math pros here could figure it out exactly.QuoteYes, in a vacuum, you'd continue to accelerate with no drag. You'd be going like 1,000 mph (a guess) when you hit the ground.
There is the conflict of other gravitational attractions.
There is a spot between the Earth and the moon that
provides an equal attraction. There used to be a
group called the "L5 Society". It wanted a stable
space colony by 1995.
L5—a stable point in empty space where the gravities of Earth and Moon are balanced, so objects, including space colonies, will stay put forever. That was where they wanted to put it,
as a step-off point for space travel.
Hence their slogan, "L5 in '95!"
Go out far enough, and you might be headed for
another planet.
Its kind of fun to play around with the numbers. Here is calculator for those that are curious.
Use 98 meters per second squared (the acceleration due to gravity on Earth), and an initial velocity of zero. Even after 10 seconds you'd be going over 2,000 miles per hour.
http://www.ajdesigner.com/constantacceleration/cavelocity.php
Use 98 meters per second squared (the acceleration due to gravity on Earth), and an initial velocity of zero. Even after 10 seconds you'd be going over 2,000 miles per hour.
http://www.ajdesigner.com/constantacceleration/cavelocity.php
QuoteIts kind of fun to play around with the numbers. Here is calculator for those that are curious.
Use 98 meters per second squared (the acceleration due to gravity on Earth), and an initial velocity of zero. Even after 10 seconds you'd be going over 2,000 miles per hour.
http://www.ajdesigner.com/constantacceleration/cavelocity.php
Attraction varies with the distance from the Earth, so
that is not a constant.
Obviously, you can get far enough away that you
are not even attracted by gravity.
QuoteQuoteIts kind of fun to play around with the numbers. Here is calculator for those that are curious.
Use 98 meters per second squared (the acceleration due to gravity on Earth), and an initial velocity of zero. Even after 10 seconds you'd be going over 2,000 miles per hour.
http://www.ajdesigner.com/constantacceleration/cavelocity.php
Attraction varies with the distance from the Earth, so
that is not a constant.
Obviously, you can get far enough away that you
are not even attracted by gravity.
Yeah, but at 14,000 feet, the number is so close to 9.8 meters per second squared, that you can use that in simulations with relative accuracy.
I was off by a decimal place too. I previously wrote 98 instead of 9.8! Makes a big difference!
I believe that if you started 100,000 miles out or so you'd be close to escape velocity http://en.wikipedia.org/wiki/Escape_velocity when you hit.Quote
Seems to me that if you have reached escape velocity you would not hit, that's the point. If you were going the same speed on a different vector you may achieve escape velocity, but since velocity contains vector, I don't believe it is achievable in the direction of the planet.
The other problem with your idea is that the only force involved to accelerate your smaller mass is gravity. That is precisely the force you are trying to overcome with escape velocity. Using force F1 to overcome force F1 would violate the second law of thermodynamics
muff528 3
QuoteYou're mixing your apples and oranges scientifically. Weight is measure of mass in a gravitational field. Vacuum is the absence of atmosphere. People often confuse those points because they equate weightlessness with being in orbit around the Earth. According to your logic, the astronauts would have been weightless on the moon, not just much lighter. An object in an evacuated bell jar on Earth would drift around weightlessly, mindless of the gravity affecting every other object on the planet.QuoteIn vacuum, weight is irrelevant, only mass is relevant. Weight is the function of gravitational acceleration between two objects.
As usual, Happythoughts logic was impeccable.
A mass accelerated by a gravitational field (unimpeded by externally applied forces like air or a scale or thrusters, etc.) has no weight at all, hence the term "weightlessness". Weight appears only when the mass is not allowed to accelerate naturally in the field. Weight = mass of the object X acceleration of gravity and is related to F=ma. Weight is really a measure of the force applied by a massive object accelerating in one reference frame to another massive object accelerating in another frame. A ball can weigh 3 pounds when weighed on a scale resting on the surface of the earth.......or the earth can weigh 3 pounds on a scale resting on the surface of the ball. No difference.
JohnMitchell 14
QuoteI believe that if you started 100,000 miles out or so you'd be close to escape velocity http://en.wikipedia.org/wiki/Escape_velocity when you hit.Quote
Seems to me that if you have reached escape velocity you would not hit, that's the point. If you were going the same speed on a different vector you may achieve escape velocity, but since velocity contains vector, I don't believe it is achievable in the direction of the planet.
The other problem with your idea is that the only force involved to accelerate your smaller mass is gravity. That is precisely the force you are trying to overcome with escape velocity. Using force F1 to overcome force F1 would violate the second law of thermodynamics
Reread the article. It states that escape velocity works regardless of vector, except for "downward". If you are accelerating directly at the planet, you will hit it.
Kinetic energy away from a gravitational field coverts, through slowing and height, to potential energy. Once you begin to fall back, potential energy converts back to the original kinetic energy, with losses for friction, yes. Since we're talking about "in a vacuum", friction losses should be a minor factor.
QuoteQuoteYou're mixing your apples and oranges scientifically. Weight is measure of mass in a gravitational field. Vacuum is the absence of atmosphere. People often confuse those points because they equate weightlessness with being in orbit around the Earth. According to your logic, the astronauts would have been weightless on the moon, not just much lighter. An object in an evacuated bell jar on Earth would drift around weightlessly, mindless of the gravity affecting every other object on the planet.QuoteIn vacuum, weight is irrelevant, only mass is relevant. Weight is the function of gravitational acceleration between two objects.
As usual, Happythoughts logic was impeccable.
A mass accelerated by a gravitational field (unimpeded by externally applied forces like air or a scale or thrusters, etc.) has no weight at all, hence the term "weightlessness". Weight appears only when the mass is not allowed to accelerate naturally in the field. Weight = mass of the object X acceleration of gravity and is related to F=ma. Weight is really a measure of the force applied by a massive object accelerating in one reference frame to another massive object accelerating in another frame. A ball can weigh 3 pounds when weighed on a scale resting on the surface of the earth.......or the earth can weigh 3 pounds on a scale resting on the surface of the ball. No difference.
The same ball weighs approximately 1/2lb on the moon, in a vacuum.
muff528 3
QuoteQuoteQuoteYou're mixing your apples and oranges scientifically. Weight is measure of mass in a gravitational field. Vacuum is the absence of atmosphere. People often confuse those points because they equate weightlessness with being in orbit around the Earth. According to your logic, the astronauts would have been weightless on the moon, not just much lighter. An object in an evacuated bell jar on Earth would drift around weightlessly, mindless of the gravity affecting every other object on the planet.QuoteIn vacuum, weight is irrelevant, only mass is relevant. Weight is the function of gravitational acceleration between two objects.
As usual, Happythoughts logic was impeccable.
A mass accelerated by a gravitational field (unimpeded by externally applied forces like air or a scale or thrusters, etc.) has no weight at all, hence the term "weightlessness". Weight appears only when the mass is not allowed to accelerate naturally in the field. Weight = mass of the object X acceleration of gravity and is related to F=ma. Weight is really a measure of the force applied by a massive object accelerating in one reference frame to another massive object accelerating in another frame. A ball can weigh 3 pounds when weighed on a scale resting on the surface of the earth.......or the earth can weigh 3 pounds on a scale resting on the surface of the ball. No difference.
The same ball weighs approximately 1/2lb on the moon, in a vacuum.
Yeah, and the moon only weighs ~1/2 pound from the ball's point of view. Vacuum is mostly irrelevant.
To the original poster - it sounds like your friends are as dense as mine!
Edit to add:
I forgot to add that the mass of an object in a vacuum has no effect on fall rate. All objects (regardless of mass) fall at the same rate of acceleration.
Here's the math, I won't bother to write it all out here.
http://www.grc.nasa.gov/WWW/K-12/airplane/ffall.html
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