RE: For the physicists in the house.

RE: For the physicists in the house. (Full Version)

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Musicmystery -> RE: For the physicists in the house. (1/3/2013 9:53:48 AM)
quote: And, how many million megatons of heat are decending upon our earth from the sun at any given instant? How much does the light weigh that we see around us on our earth? The mass of the photons (light) from the sun striking the earth every second is 2.5 kg/s. quote: Since sunlight has energy, it also has a mass associated with it as indicated by Einstein's famous equation E = mc^2 or m = E/(c^2). An elementary textbook says the sun converts 4.2 x 10^9 kg of mass to energy every second. Using this number, we can estimate the amount of energy (mass) from the sun hitting the earth by calculating the fraction of the entire solid angle the earth intercepts as seen by the sun. Since the diameter of the earth is about 1.3 x 10^7 m and it is 1.5 x 10^11 m from the sun, it subtends an angle of about 8.7 x 10^-5 radians. If we square this angle and divide by 4 pi = 12.6, we get the solid angle fraction subtended by the earth, which I calculate to be about 6 x 10^-10 of the entire solid angle. Multiplying this by the 4.2 x 10^9 kg burned by the sun every second and we obtain 2.5 kg/s as the mass of the photons (light) from the sun striking the earth every second. There is another way to guesstimate this number using the rough estimate of 1 kW/m^2 as the energy of the sunlight striking the earth. Multiplying this by the area of a disk with the area of the cross section of the earth (pi x R^2 = 1.3 x 10^14 m^2) gives 1.3 x 10^17 J/s. Dividing this by the velocity of light squared (c^2 = 9 x 10^16) gives 1.4 kg/s. I consider this to be in excellent agreement with the figure of 2.5 kg/s obtained above. Please let me know if you find this less than clear or would like more information or explanation. Best, Dick Plano, Professor of Physics emeritus, Rutgers University http://www.newton.dep.anl.gov/askasci/phy00/phy00644.htm

Hillwilliam -> RE: For the physicists in the house. (1/3/2013 9:56:35 AM)
quote: ORIGINAL: Musicmystery quote: And, how many million megatons of heat are decending upon our earth from the sun at any given instant? How much does the light weigh that we see around us on our earth? The mass of the photons (light) from the sun striking the earth every second is 2.5 kg/s. quote: Since sunlight has energy, it also has a mass associated with it as indicated by Einstein's famous equation E = mc^2 or m = E/(c^2). An elementary textbook says the sun converts 4.2 x 10^9 kg of mass to energy every second. Using this number, we can estimate the amount of energy (mass) from the sun hitting the earth by calculating the fraction of the entire solid angle the earth intercepts as seen by the sun. Since the diameter of the earth is about 1.3 x 10^7 m and it is 1.5 x 10^11 m from the sun, it subtends an angle of about 8.7 x 10^-5 radians. If we square this angle and divide by 4 pi = 12.6, we get the solid angle fraction subtended by the earth, which I calculate to be about 6 x 10^-10 of the entire solid angle. Multiplying this by the 4.2 x 10^9 kg burned by the sun every second and we obtain 2.5 kg/s as the mass of the photons (light) from the sun striking the earth every second. There is another way to guesstimate this number using the rough estimate of 1 kW/m^2 as the energy of the sunlight striking the earth. Multiplying this by the area of a disk with the area of the cross section of the earth (pi x R^2 = 1.3 x 10^14 m^2) gives 1.3 x 10^17 J/s. Dividing this by the velocity of light squared (c^2 = 9 x 10^16) gives 1.4 kg/s. I consider this to be in excellent agreement with the figure of 2.5 kg/s obtained above. Please let me know if you find this less than clear or would like more information or explanation. Best, Dick Plano, Professor of Physics emeritus, Rutgers University http://www.newton.dep.anl.gov/askasci/phy00/phy00644.htm But don't forget that the earth is simultaneously reradiating almost exactly the same via reflectance and infra red.

Musicmystery -> RE: For the physicists in the house. (1/3/2013 3:05:48 PM)
Ah . . . no.

mnottertail -> RE: For the physicists in the house. (1/3/2013 3:08:40 PM)
If we gave off like we got our average temperature would be -18C year round. http://oceanworld.tamu.edu/resources/oceanography-book/radiationbalance.htm There's more but pictures are easy. Be sure to watch the animation.

epiphiny43 -> RE: For the physicists in the house. (1/3/2013 3:24:10 PM)
The problem is that temperature is a metric of energy, and energy has mass, but the temps we experience mean kinetic motions that are only relativistically Very small. Increase in kinetic energy (vibration of molecules) increases mass but only in relation to that Delta (change of) speed divided by C, the speed of light. This is hard to measure with common household objects?

LookieNoNookie -> RE: For the physicists in the house. (1/3/2013 6:24:36 PM)
quote: ORIGINAL: Aswad Is, by mass-energy equivalence, the thermal energy of an object part of its effective gravitational mass? Or, phrased differently, does the gravitation of an object depend in part on its heat? The intuitive answer seems to be yes, but IANAP. IWYW, — Aswad. Interesting that you pose that.... First, mass energy equivalence is only transposed by virtue of the heat deflection that is dispersed by its own tangent (which can, as most might know, be expressed by no less than X= 7/23 plus the obvious [23/11th at gravity (assuming gravity at 1.71375) less the assumptions of least path, over dynamic reference] belying of course all the obvious assumptions as to gain on the 4th pull...plus the second dynamic. Which is of course to say....you can't get there without doing the gravitational expressions which are by default, only in their (obvious) stack. I think that's fairly clear (to most). So, that being said, it's then more than prescient....you can't have one without the other. I believe I've expressed the obvious here. To try and differentiate between the two (clear) poles is really a waste of time and frankly....a portent to what finally results.

Hillwilliam -> RE: For the physicists in the house. (1/3/2013 6:28:37 PM)
quote: ORIGINAL: Musicmystery Ah . . . no. Are you saying the earth doesn't radiate Ir and reflect light? I beg to differ. that would make our planet a theoretical "black body" (don't get exceited ladies, Im not talking about..yaknow [8D] ) A black body absorbs all photonic energy and reradiates none. Such an entity will soon vaporize due to absorbed heat.

Musicmystery -> RE: For the physicists in the house. (1/3/2013 7:36:23 PM)
No. Now I remember why I stopped wasting time here. quote: the earth is simultaneously reradiating almost exactly the same via reflectance and infra red. That's the issue you raised. Not whether reflection and radiation happens. And neither has any relevance for the point raised in my post. I'll leave y'all to the madhouse. Knock each other out.

Aswad -> RE: For the physicists in the house. (1/4/2013 4:40:15 AM)
The actual question was one about whether an object's kinetic energy influences its gravitational mass. That said, as regards thermal radiation, a blackbody radiates based on its temperature, and absorbs as effectively as it radiates. Reflectors of thermal infrared do not radiate well. Water is a very close approximation of a blackbody. The Earth does radiate close to what it absorbs. Not sure how you arrived at the conclusion that blackbodies don't radiate, Hillwilliam. IWYW, — Aswad.

mnottertail -> RE: For the physicists in the house. (1/4/2013 5:50:42 AM)
quote: ORIGINAL: epiphiny43 The problem is that temperature is a metric of energy, and energy has mass, but the temps we experience mean kinetic motions that are only relativistically Very small. Increase in kinetic energy (vibration of molecules) increases mass but only in relation to that Delta (change of) speed divided by C, the speed of light. This is hard to measure with common household objects? Precisely, and that is why you can use newton for most gravity and inertia and mass calculations (only when very big or very very small or very fast do we have to go out with a better class of girl and get the better answer). The earth is not round, but for most discussions, it will work.

Hillwilliam -> RE: For the physicists in the house. (1/4/2013 5:54:34 AM)
quote: ORIGINAL: Aswad The actual question was one about whether an object's kinetic energy influences its gravitational mass. That said, as regards thermal radiation, a blackbody radiates based on its temperature, and absorbs as effectively as it radiates. Reflectors of thermal infrared do not radiate well. Water is a very close approximation of a blackbody. The Earth does radiate close to what it absorbs. Not sure how you arrived at the conclusion that blackbodies don't radiate, Hillwilliam. IWYW, — Aswad. I was using an example of a theoretical body that only absorbs energy and never reradiates. By definition, such a body wouldn't last long unless it had several stellar masses and therefore would be able to collapse into a singuarity. Otherwise, the temperature would get so high, it would vaporize. I said theoretical because I know of no body above absolute zero that isn't a singularity that doesn't radiate.

mnottertail -> RE: For the physicists in the house. (1/4/2013 5:57:57 AM)
collapsed stars are hot, because they are collapsed.

Hillwilliam -> RE: For the physicists in the house. (1/4/2013 5:59:54 AM)
quote: ORIGINAL: mnottertail collapsed stars are hot, because they are collapsed. Black holes don't radiate photonic energy though. The accretion disk does but the singularity itself doesnt.

mnottertail -> RE: For the physicists in the house. (1/4/2013 6:02:47 AM)
Agreed but that is because the radiation cannot escape the gravity of the mass, but it is one nasty motherfucker inside that horizon. and you can quote me.

mnottertail -> RE: For the physicists in the house. (1/4/2013 6:08:48 AM)
Basics again. E = M( c*c) it is squared to get the units right. but looking at the thing, we realize that c is a constant........ unchangeable. How do we get more E? increase M. How do we get more M? increade E. end of joke. (M of course since it is a multiplied dealio is making the greater stride.

jlf1961 -> RE: For the physicists in the house. (1/4/2013 6:44:07 AM)
Only physics I know is what the army taught me. 10lbs of C4+blasting medium= one nice big boom.

kdsub -> RE: For the physicists in the house. (1/4/2013 11:48:42 AM)
quote: The actual question was one about whether an object's kinetic energy influences its gravitational mass I always think in basic terms...simple where possible. The above statement has been in my thoughts for sometime and I have gotten conflicting, at least with me and seeming common sense, answers to this question from a civil engineer and a science teacher at our high school. Granted neither would be considered experts…but neither are we. The question I asked them which is essentially the same statement above is. If I placed my foot in a pothole, exactly fitting side to side and exactly matching the top of the hole, in the highway on top of a precise scale and drove a vehicle over my foot at 10 miles per hour and at 100 miles per hour would the reading on the scale, when the vehicle passed over my foot, be to same. Otherwise would the forward speed of the vehicle reduce its weight on the road. The same example could be uses with shooting a bullet. Both say no.. the reading on the scale would be exactly the same. The only difference would be the duration of weight. So the answer to the question Aswad would be no… straight line kinetic energy has no effect on gravitational mass. At least according to them…I’m not so sure. Butch

mnottertail -> RE: For the physicists in the house. (1/4/2013 11:52:23 AM)
Ek = ½mv^2 Ep=mgh Ek= Ep Ek = Kinetic Energy Ep = Potential Energy m = mass v = velocity g = acceleration due to gravity h = height so, yeah.........sorry Butch.

kdsub -> RE: For the physicists in the house. (1/4/2013 11:56:01 AM)
Ron...what the hell did you say..lol.. would the weight be the same or different. Butch

mnottertail -> RE: For the physicists in the house. (1/4/2013 1:03:19 PM)
simple math. But screw that, lets do the logic. the mass would have to increase, kinetic energy is the energy of its motion. An increase in velocity increases the mass. there isn't anything else we got to choose from in those formulas. note that the acceleration here is due to gravity, not to light speed, it is small..........very small.

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