NASA has finally agreed to fly to the moon in metric - a move its scientists have wanted ever since they mixed up kilometres with miles and crashed an expensive spacecraft near Mars.
The actual mixup was pounds (of force) and Newtons, and the JPL trajectory analysts knew that the spacecraft was off course but their managers would not listen to them when they said that a course correction was needed. That was real cause of the accident. Moral of the story: when your highly educated expert employee tells you that he doesn't understand what is going on, you better drop everything and get to the bottom of the mystery before disaster happens.
On the other hand many caculations are simplified with metrics, wavelength for example. Amps, Volts, Farads, Henrys, Ohms, Frequency, and Watts are same in metric and need no conversion.
The electrical units are NOT "the same in metric", they ARE metric!!!
My pet metric peeves:
Newspaper and magazine editors (probably English majors) who quote excessive precision when converting from metric to US units, as in "the asteroid is estimated to have a diameter of 1000 kilometers (620 miles)". The scientist they interviewed does not know the diameter to more than one significant figure, so quoting 620 miles is absurd.
The same editors also convert rocket thrust from pounds (of force) into kilograms, because they don't know that pounds can measure mass or force and these ARE NOT THE SAME THING! In respected scientific publications I see statements such as "the 100 pound (45.3 kilogram) rocket thrusters..." when they SHOULD have written "the 100 pound (400 Newton) rocket thrusters....".
As a teaching assistant in the freshman "physics for pharmacists" class I was required to teach the international students about feet, inches, pounds and miles when I should have been teaching the US students how to do physics in metric units.
It is however a fact of life that both systems of units will be around for quite some time, and engineers in the United States need to be fully conversant in both systems of measurements. And if I find a nice South Bend lathe on E-bay I'm not going to pass it up just because it wasn't made for metric machining.
Dan Schultz N8FGV
Ah, the mass/weight confusion. Agree with you on that. And no, most such writers don't handle unit conversions in anything like an intelligent way (and I've seen far worse examples, some going to 2 or 3 decimal places ..)
Sometimes I wish more people understood the difference between mass and weight, and the difference between energy and power. It would cut down on some of the gibberish.
On Jan 21, 2007, at 4:58 PM, Daniel Schultz wrote:
The same editors also convert rocket thrust from pounds (of force) into kilograms, because they don't know that pounds can measure mass or force and these ARE NOT THE SAME THING! In respected scientific publications I see statements such as "the 100 pound (45.3 kilogram) rocket thrusters..." when they SHOULD have written "the 100 pound (400 Newton) rocket thrusters....".
--... ...-- -.. . -. ..... ...- -... Bruce Bostwick N5VB
At 12:51 PM 1/22/2007, Bruce Bostwick wrote:
Ah, the mass/weight confusion. Agree with you on that. And no, most such writers don't handle unit conversions in anything like an intelligent way (and I've seen far worse examples, some going to 2 or 3 decimal places ..)
True...
Sometimes I wish more people understood the difference between mass and weight, and the difference between energy and power. It would cut down on some of the gibberish.
That's for sure. It's amazing how many people don't know the difference. Not helped when the mainstream media talks about "body weight problems" when it's really a problem of excess mass. You can reduce your weight by 100% easily, if you have a spare $20 million. Book a vacation on the ISS! ;) But it's only temporary, it all comes back when you reach the ground! ;)
73 de VK3JED http://vkradio.com
Tony Langdon wrote: --- snip --
That's for sure. It's amazing how many people don't know the difference. Not helped when the mainstream media talks about "body weight problems" when it's really a problem of excess mass. You can reduce your weight by 100% easily, if you have a spare $20 million. Book a vacation on the ISS! ;) But it's only temporary, it all comes back when you reach the ground! ;)
Tony,
Are you really weightless in space? Surely you're just in free fall. When the term "weightless" is used to describe the condition astronauts experience, this is surely a literary term, rather than a scientific one.
Why spend the $20.000.000 (or 20,000,000 if that's your custom) you mention, when you could achieve that same "weightlessness" by jumping out of a building (if for a shorter time, of course, and with a riskier outcome).
Am I weightless when I jump off a chair?
Are orbiting satellites "weightless"?
Or are they just falling down all the time (in a very special way but because of their weight).
If a satellite falls down in the special way we call an orbit because the planet's gravity is acting on it's mass, isn't that weight?
So... wouldn't a "weightless" satellite barrel off on a straight line?
Sil
At 03:38 PM 1/22/2007, Sil - ZL2CIA wrote:
Are you really weightless in space? Surely you're just in free fall. When the term "weightless" is used to describe the condition astronauts experience, this is surely a literary term, rather than a scientific one.
As it turns out, the answer is "yes" or "no". It depends on your frame of reference and the definition you use. Using the definition that weight is the force exerted by gravity, then one would presume at a point near the Earth - Moon L1 point, you would be very nearly weightless (there would be some unbalanced gravitational influence of the Sun most of the time, but you could move around and null that out too...).
Why spend the $20.000.000 (or 20,000,000 if that's your custom) you mention, when you could achieve that same "weightlessness" by jumping out of a building (if for a shorter time, of course, and with a riskier outcome).
A _much_ shorter time (remember air resistance quickly builds up so you soon have the same reaction force from air resistance as you do standing on the ground - i.e. you quickly reach terminal velocity).
Am I weightless when I jump off a chair?
Depends who you ask, but most physics sources do say "no" as they define weight purely in terms of gravitation.
Are orbiting satellites "weightless"?
See above, but after looking at a number of sources, I'll concede "no" (assuming the strict gravitational definition of weight).
73 de VK3JED http://vkradio.com
On 22 Jan 2007 at 17:43, Tony Langdon wrote:
At 03:38 PM 1/22/2007, Sil - ZL2CIA wrote:
There is a lot of folks who experience free falls in their dreams...it is probably not related to gravity but as much scary than a real one. Could be a dream interpreter can be usefull here.
As Einstein says all is relative to the context the astronauts are falling but they don't feel it as they remain at the same level.
Is the astronauts make also free falling dreams?
Back to normal programming...
Are you really weightless in space? Surely you're just in free fall. When the term "weightless" is used to describe the condition astronauts experience, this is surely a literary term, rather than a scientific one.
As it turns out, the answer is "yes" or "no". It depends on your frame of reference and the definition you use. Using the definition that weight is the force exerted by gravity, then one would presume at a point near the Earth - Moon L1 point, you would be very nearly weightless (there would be some unbalanced gravitational influence of the Sun most of the time, but you could move around and null that out too...).
Why spend the $20.000.000 (or 20,000,000 if that's your custom) you mention, when you could achieve that same "weightlessness" by jumping out of a building (if for a shorter time, of course, and with a riskier outcome).
A _much_ shorter time (remember air resistance quickly builds up so you soon have the same reaction force from air resistance as you do standing on the ground - i.e. you quickly reach terminal velocity).
Am I weightless when I jump off a chair?
Depends who you ask, but most physics sources do say "no" as they define weight purely in terms of gravitation.
Are orbiting satellites "weightless"?
See above, but after looking at a number of sources, I'll concede "no" (assuming the strict gravitational definition of weight).
73 de VK3JED http://vkradio.com
Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe WAC BASIC CW PHONE SATELLITE
OK, But what is a quick rule of thumb to determine the number if threads per cm from pitch? Threads per inch is a simple concept and easy to apply and measure. Metric bolts with pitch in degrees is something I can't easily relate to.
Art, KC6UQH ----- Original Message ----- From: "Luc Leblanc" lucleblanc6@videotron.ca To: amsat-bb@amsat.org Sent: Monday, January 22, 2007 2:33 AM Subject: [amsat-bb] Re: AMSAT-NA totally metric? and now almost totally off topic.
On 22 Jan 2007 at 17:43, Tony Langdon wrote:
At 03:38 PM 1/22/2007, Sil - ZL2CIA wrote:
There is a lot of folks who experience free falls in their dreams...it is probably not related to gravity but as much scary than a real one. Could be a dream interpreter can be usefull here.
As Einstein says all is relative to the context the astronauts are falling but they don't feel it as they remain at the same level.
Is the astronauts make also free falling dreams?
Back to normal programming...
Are you really weightless in space? Surely you're just in free fall. When the term "weightless" is used to describe the condition astronauts experience, this is surely a literary term, rather than a scientific one.
As it turns out, the answer is "yes" or "no". It depends on your frame of reference and the definition you use. Using the definition that weight is the force exerted by gravity, then one would presume at a point near the Earth - Moon L1 point, you would be very nearly weightless (there would be some unbalanced gravitational influence of the Sun most of the time, but you could move around and null that out too...).
Why spend the $20.000.000 (or 20,000,000 if that's your custom) you mention, when you could achieve that same "weightlessness" by jumping out of a building (if for a shorter time, of course, and with a riskier outcome).
A _much_ shorter time (remember air resistance quickly builds up so you soon have the same reaction force from air resistance as you do standing on the ground - i.e. you quickly reach terminal velocity).
Am I weightless when I jump off a chair?
Depends who you ask, but most physics sources do say "no" as they define weight purely in terms of gravitation.
Are orbiting satellites "weightless"?
See above, but after looking at a number of sources, I'll concede "no" (assuming the strict gravitational definition of weight).
73 de VK3JED http://vkradio.com
Luc Leblanc VE2DWE Skype VE2DWE www.qsl.net/ve2dwe WAC BASIC CW PHONE SATELLITE
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
participants (6)
-
Bruce Bostwick -
Daniel Schultz -
kc6uqh -
Luc Leblanc -
Sil - ZL2CIA -
Tony Langdon