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Oct
31
asked Why does gravity conserve linear momentum but not forces at a pivot point?
Aug
15
comment When a star becomes a black hole, does its gravitational field strength become stronger?
@JohannesD Ah, I think I understand it now. Counter-intuitive, but cool! Think I need to play KSP sometime...
Aug
14
comment When a star becomes a black hole, does its gravitational field strength become stronger?
@JohannesD (LOL, my comment's upvotes.) I see, but the question still remains: once you get out of Earth's orbit (which you have to do in any of these situations), what orbit is there to get out of? (Unrelated, but wouldn't air resistance — which would be too weak to fit in reasonable timescales, but still would exist — eventually slow it down and bring the orbiter down crashine?)
Aug
14
comment When a star becomes a black hole, does its gravitational field strength become stronger?
"The reason is that takes a lot of energy (a whole lot of energy!) to get to Mercury. Escaping the solar system is a piece of cake compared to getting to Mercury. It would take even more energy to get very close to the surface of the Sun." I can understand that escaping from orbit around Mercury or the Sun, or indeed not crashing into them at all would be very difficult; but talking about just getting till there, wouldn't going towards a massive object be easier than going away from it due to gravity?
Jul
5
comment Why is filling a balloon from your mouth much harder initially?
@BrockAdams mentions a secondary, but still very important (at least, in the case of old balloons stored in a closet for a long time) point: Stretch a balloon before inflating it. It returns to almost it's exact starting shape if you don't overdo it. Yet it is now much easier to blow up. The stickiness of rubber does affect the difficulty a lot.
Jun
29
comment What really allows airplanes to fly?
A block-quote or more extensive description would be more helpful than just the link.
Jun
24
awarded  Scholar
Jun
24
accepted Velocity of 2 balls with different masses on a moving train after the train brakes
Jan
12
awarded  Popular Question
Nov
17
revised How was Avogadro's number first determined?
Fixed grammar and sentence structure; Changed the question in the brackets to a doubt that would actually make sense (see <http://physics.stackexchange.com/questions/13757/how-was-avogadros-number-first-determined#comment71207_13757>);
Nov
17
comment How was Avogadro's number first determined?
@SteveB Exactly! I think what the OP meant was "How could we know the charge of a single electron just by knowing the charge of a mole of electrons without knowing the ratio of the number of particles in both?". Presumably, he didn't know that that was exactly how Avogadro's number was first discovered.
Nov
17
suggested approved edit on How was Avogadro's number first determined?
Jul
24
comment Is there a proof of existence of time?
@babou The thermodynamic, physcological and cosmological arrows of time seem to flow in tha same direction, but then in another model there's this concept of 'imaginary' time in which time and the 3 space dimensions exist in Euclidean space-time (i.e., there's nothing fundamentally different between all the 4 dimensions). In that model, there is no preferred direction of low. In the common model, there is.
Jul
24
revised Which parameter determines how much the 'recoil' or force applied by an object hurts?
Retagged;
Jul
24
comment Which parameter determines how much the 'recoil' or force applied by an object hurts?
Hmmm... the shoulder ability would surely be of no consequence at such high speeds. It's definitely the lighter rifle then...
Jul
24
comment Which parameter determines how much the 'recoil' or force applied by an object hurts?
10x for the analogy!
Jul
24
comment Velocity of 2 balls with different masses on a moving train after the train brakes
No, that was not the source of my confusion. I'd mistakenly read the statement as "I disagree with the fact that the statement was being attributed to your teacher" and not as " I disagree with the statement that you had attributed to your teacher". Sorry...
Jul
23
asked Which parameter determines how much the 'recoil' or force applied by an object hurts?
Jul
23
comment Velocity of 2 balls with different masses on a moving train after the train brakes
+1'd, 10x for the answer. I understood the answer and it was quite detailed :) But I didn't quite get your second statement: "I disagree with the statement attributed to your teacher".
Jul
23
revised Velocity of 2 balls with different masses on a moving train after the train brakes
Replaced 'roll of' with 'slide off';