dawson Posted April 7, 2013 Share Posted April 7, 2013 If you've got nothing to do, come and mow my lawn Link to comment Share on other sites More sharing options...
Tibbz2 Posted April 7, 2013 Share Posted April 7, 2013 Haha, I feel Nottingham may be a bit of a trek for that! Link to comment Share on other sites More sharing options...
dawson Posted April 7, 2013 Share Posted April 7, 2013 Link to comment Share on other sites More sharing options...
dawson Posted April 7, 2013 Share Posted April 7, 2013 Right, well that was fascinating, but largely over my head. At least I understand now why a black hole with infinite gravity isn't pulling me in; I'm just too far away. Thanks for the link Mike. James Link to comment Share on other sites More sharing options...
Tibbz2 Posted April 7, 2013 Share Posted April 7, 2013 Very good lecture indeed, helped refresh my memory on the basics which I will probably need soon, thanks! Link to comment Share on other sites More sharing options...
dawson Posted April 7, 2013 Share Posted April 7, 2013 Why will you need it soon? Link to comment Share on other sites More sharing options...
Tibbz2 Posted April 7, 2013 Share Posted April 7, 2013 Why will you need it soon? Back to school, plenty of physics talk! Also I think we have a section on astronomy in our Physics A Level course starting September Link to comment Share on other sites More sharing options...
dawson Posted April 7, 2013 Share Posted April 7, 2013 At. I see. I hadn't realised you were so young. Make the most of it while you can. It's all down hill from about 25 James Link to comment Share on other sites More sharing options...
Tibbz2 Posted April 7, 2013 Share Posted April 7, 2013 I will try to! Link to comment Share on other sites More sharing options...
T A WOW Posted April 7, 2013 Share Posted April 7, 2013 Whoop. (off topic) you're called tobias too. First other tobias I've ever met (sort of) Link to comment Share on other sites More sharing options...
dawson Posted April 7, 2013 Share Posted April 7, 2013 Whats the collective noun for two or more tobias's? Link to comment Share on other sites More sharing options...
Tibbz2 Posted April 7, 2013 Share Posted April 7, 2013 Whoop. (off topic) you're called tobias too. First other tobias I've ever met (sort of) Haha yes! *high five* There's someone I know who's name is Tobias but he is always called Toby (which I would hate), so technically so are you! Good point James... No idea! Link to comment Share on other sites More sharing options...
dawson Posted April 8, 2013 Share Posted April 8, 2013 In that lecture, the guy says something like "if I shone a light into a black hole, I'd be throwing photos into it, and they would add their mass energy to the mass of the black hole, and the black hole would get larger".... but then it's got zero mass, so that just doesn't make sense to me. James Link to comment Share on other sites More sharing options...
Perkil8r Posted April 8, 2013 Share Posted April 8, 2013 (edited) Aha.... Mass is the same as weight (in effect) which mustn't be confused with size. Well that isn't true as the following link explains, however in layman's terms they are similar, certainly for the purposes of this explanation. http://hyperphysics.phy-astr.gsu.edu/hbase/mass.html Edited April 8, 2013 by Perkil8r Link to comment Share on other sites More sharing options...
Guest Kheldar Posted April 8, 2013 Share Posted April 8, 2013 Aha.... Mass is the same as weight (in effect) which mustn't be confused with size. Take that back Mr Mike - mass and weight are not the same thing Link to comment Share on other sites More sharing options...
Perkil8r Posted April 8, 2013 Share Posted April 8, 2013 Take that back Mr Mike - mass and weight are not the same thing Already edited to clarify, however yes you are correct. Mass is constant, weight changes with gravity. Mass is not related to volume (or size) but mass over volume gives us density which relates to gravity. Link to comment Share on other sites More sharing options...
Tibbz2 Posted April 8, 2013 Share Posted April 8, 2013 In that lecture, the guy says something like "if I shone a light into a black hole, I'd be throwing photos into it, and they would add their mass energy to the mass of the black hole, and the black hole would get larger".... but then it's got zero mass, so that just doesn't make sense to me. James If i'm reading this right then you're wondering why massless particles add mass to the BH? In basic terms I think that photons, although they have no mass, still have energy which is added to the BH, which increases the energy/mass of the BH (as long as the photons have more energy than the BH in the first place, which they should seeing as BH are so 'cold'!) Link to comment Share on other sites More sharing options...
Perkil8r Posted April 8, 2013 Share Posted April 8, 2013 In that lecture, the guy says something like "if I shone a light into a black hole, I'd be throwing photos into it, and they would add their mass energy to the mass of the black hole, and the black hole would get larger".... but then it's got zero mass, so that just doesn't make sense to me. James A black hole has mass, and lots of it! What it does not have is much physical size, hence the enormous density and therefore gravity. Link to comment Share on other sites More sharing options...
Tibbz2 Posted April 8, 2013 Share Posted April 8, 2013 I'm confused at whether I have completely mis-interpreted the question now Link to comment Share on other sites More sharing options...
Perkil8r Posted April 8, 2013 Share Posted April 8, 2013 (edited) I'm confused at whether I have completely mis-interpreted the question now Possibly, although whilst we're talking about photons, they do have mass they behave like particles and therefore have mass, it's just rediculously small. Actually, scratch that, Photons are said to have zero mass, but the do have momentum. However for something to have momentum it must have mass. This is an area of research that is quite a hot topic for some people. I prefer the theory that they have got some mass. Edited April 8, 2013 by Perkil8r Link to comment Share on other sites More sharing options...
Tibbz2 Posted April 8, 2013 Share Posted April 8, 2013 (edited) Everything I've ever been taught is wrong! I thought they were massless, however had a relativistic mass? Edit: Ah I see. Well i'm sticking with massless until they can prove otherwise Edited April 8, 2013 by Tibbz2 Link to comment Share on other sites More sharing options...
dawson Posted April 8, 2013 Share Posted April 8, 2013 I'm not sure of the question myself either. So black holes have enormous mass, but no volume, and infinite gravity? James Link to comment Share on other sites More sharing options...
Tibbz2 Posted April 8, 2013 Share Posted April 8, 2013 Yup, a large mass packed into 'no' volume, so they're infinitely dense etc. Link to comment Share on other sites More sharing options...
Doc Posted April 8, 2013 Share Posted April 8, 2013 If I remember correctly according to Einstein black holes are simply made up of gravitational energy. Anything that is sucked into a black hole is converted to energy. Black holes have mass but do not contain matter and apparently are not black. Link to comment Share on other sites More sharing options...
dawson Posted April 8, 2013 Share Posted April 8, 2013 OK. I can comprehend that. And if I threw my old car battery in, it's mass would increase by the mass of a car battery, but it's volume would remain zero as the battery would be squished down to zero volume too....? James Link to comment Share on other sites More sharing options...
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