why a candle's flame direction is always upward? What is the coposition of fire? Don't say it's energy. There is something else.
2757
I was watching  today, and noticed this: in some moment the space station changed orbit and the people inside experienced zero-gravity. At that moment, a candlestick passed floating in the air, with the candles burning ().   But in our environment the flames go upward because the hot air is less dense, and that effect should disappear when no gravity is present, am I right? How would a candle flame look then?
77048
Is  a ?  If not, what is it then?  If yes why, don't we teach kids this basic example?    UPDATE: I probably meant a regular commonplace fire of the usual temperature. That should simplify the answer.
31900
Alternatively, why does the force created by blowing out air feel so much stronger than the force created by sucking in air?  Ok, so forget the human factor involved in blowing out candles. Consider a vacuum cleaner with a suction end and a blower end. Anyone who has tried it out notices the blower end creates a much stronger force than the suction end, despite the discharge being (more or less) equal at both ends.  Why does this happen?
78728
Recently I read an interesting article about . I was puzzled because I thought before that  has definite meaning in thermodynamics: it tells about how fast atoms jiggle. Now if temperature can be negative, this means temperature has wider meaning...  I wonder if there is any deep physical meaning of temperature, not mathematical one.
9398
I've been looking for questions about dark matter, and I've read some very interesting answers. However, I desire too look into it deeply.   This is not actually a question. I'm asking the community to recommend interesting references to understanding dark matter and dark energy.   I accept all sort of references: notes, books, scientific papers etc.  Let us assume some background on classical physics, thermodynamics and basics about quantum theory.
32101
Why does hot air rise?  I did an experiment:  I made a model of hot air and cool air with marshmallows and toothpicks. The hot air had more volume than the cold air. Then, I weighed it. They both weighed the same, even though they had a different volume.  So I don't understand why does hot air rise?
24097
With the wording of , it seems like you take the cast the spell action to make the flame appear.  You can then attack with it later - it does use the wording "ranged spell attack."  It never addresses what you can do with it otherwise, even though you are still holding a handful of flame.     What if a tavern brawler or a Monk punches with the hand holding the flame, or uses that hand to make a special melee attack (grapple or push?)      Would that be considered a spell attack, or an unarmed strike because the hand is passively holding the flame?  Could you use the flame as an improvised weapon?    Or would it be something else?  Note: I am making a character for a silly one shot. I am not planning on trying to pull this off for a serious campaign, but it is worth trying as a goofy concept. This side note probably won't affect any answers but I wanted to include it anyway.
43459
I am starting to see a lot of people claiming that convential current is 'wrong' because Franklin made an error when he first started investigating electrostatics, and that later scientists didn't bother correcting the mistake, but preferred to keep the 'convention' (here is a classic example: )  I always thought he didn't get it wrong. He said that current is positive in the direction that positive charge flows, and vice-versa. He of course had no way to know which side of two sticks behind rubbed actually gained or lost mass. So he wasn't wrong. What were you taught?  P.S. I can't help but feel we are lucky that he got it 'backwards', because clearly many people are confused about electrostastics (including the author of that text book!) and believe electricity has to involve electrons (an unfortunate name... why couldn't they have been named negatrons...)
89979
The chimney in the picture above is more than 20m high. The chimney in the picture above is more than 20m tall.   Are both high and tall proper in these sentences?   If not, why not? And when should one prefer high over tall, and vice versa?
51053
Why does light have the speed it does? why is it not considerably faster or slower than it is?  I can't imagine science, being what it is, not pursuing a rational scientific explanation for the speed of light.  Just saying "it is what it is" or being satisfied saying it is 1 ($c=1$), does not sound like science.
49652
Eragon and Arya asked Angela how she killed twenty men at once she said  What is time but motion? What is motion but heat? And are not heat and energy but different names for the same thing? When you understand the implications of that, you'll understand how and what I did.  What does she mean and how does this explain what she did?
68714
The text of the  spell reads:      A flickering flame appears in your hand. The flame remains there for the duration and harms neither you nor your equipment. The flame sheds bright light in a 10-foot radius and dim light for an additional 10 feet. The spell ends if you dismiss it as an action or if you cast it again.   Emphasis mine. The druid in our party asked our DM if he is able to cast produce flame in a dark cave, then opt not to attack with it, and wield a shield and sword. The goal is to continue emitting light, since he doesn't have the light spell. He claims that since the flame does not harm his equipment, he is able to hold a shield or sword with the fiery hand with no problem.  Is this okay to do RAW, or are we missing something?  This is specifically not asking about casting spells with a sword in hand. He wants to draw his weapon after casting and holding the flames.  Related, but not the same question: , , .
106650
I have found that light always produces heat. The only cases I think heat is absent with light is  and  (maybe because they emit low energy but maybe the heat is still present?). So my question is: Is heat energy always present when light is emitted, specially for bright light(more energy)?    If some example or any links can be provided, then it will be very helpful.
108587
Why does the nature always prefer low energy and maximum entropy?  I've just learned electrostatics and I still have no idea why like charges repel each other.  I don't quite understand why U has to be minimum. Can someone explain?
101128
Why is the shape of the  (or an electric spark) always of a zig-zag nature? Why is it never just a straight line?     .
85305
In many pieces of literature, light is said to travel like a "wave". Does this mean the light literally propagates through space like a wave as in up and down and so on or does light move linearly through space? Also, if it move linearly, why do we say photons are a wave then?
33949
Suppose we are given a stick and a stone tied to the stick by a string. Now if we rotate the stone around the stick the stone rises in height (see picture below). My question is which force accounts for this rise in height?     According to me (please correct me if I am wrong) this happens due to centrifugal force. The centrifugal force is directed along the string outwards, so we can resolve it into two components, one is the horizontal component and the other is the vertical component. If the mass of the stone is m, its velocity is v, the length of the string is r, and the angle the string makes with the horizontal is θ, then the total centrifugal force is mv^2/r, the horizontal component of the centrifugal force is mv^2/r * cos(θ), and its vertical component is mv^2/r * sin(θ) (see picture below). Can anyone tell me if I am correct? The directions of the forces are given in the picture, but I am not sure whether the directions are right or not. Also note that in the second picture for sake of clarity I have not drawn the direction of rotation of the stone.