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26
votes
4answers
10k views

Why can't energy be created or destroyed?

My physics instructor told the class, when lecturing about energy, that it can't be created or destroyed. Why is that? Is there a theory or scientific evidence that proves his statement true or ...
14
votes
3answers
687 views

Accidental, unplanned breakthroughs in physics [closed]

There is possibly some idioms or saying like this, ``If you try too hard for something, you will never get it. If you do not aim for something, it may fall on you accidentally, not as you originally ...
13
votes
11answers
24k views

How do you start self-learning physics [closed]

I think this question has its place here because I am sure some of you are "self-taught experts" and can guide me a little through this process. Considering that : I don't have any physics scholar ...
12
votes
5answers
873 views

units and nature

I am wondering whether the five$^1$ units of the natural unit system really is dictated by nature, or invented to satisfy the limited mind of man? Is the number of linearly independent units a ...
11
votes
7answers
1k views

Is physics rigorous in the mathematical sense?

I am a student studying Mathematics with no prior knowledge of Physics whatsoever except for very simple equations. I would like to ask, due to my experience with Mathematics: Is there a set of ...
8
votes
4answers
317 views

What fundamental principles or theories are required by modern physics?

We have been taught that speed of light is insurmountable but as we know an experiment recently tried to show otherwise. If the experiment did turn out to be correct and confirmed by others, would ...
7
votes
6answers
5k views

Can a scientific theory ever be absolutely proven?

I personally cringe when people talk about scientific theories in the same way we talk about everyday theories. I was under the impression a scientific theory is similar to a mathematical proof; ...
7
votes
2answers
12k views

Why do car keys have longer range when held next to your head?

I first saw this on Top Gear, and assumed it was a load of rubbish, but today I tried it out and it actually works, if you walk away from the car continuously unlocking/locking it until it stops, and ...
7
votes
3answers
2k views

Interesting topics to research in mathematical physics for undergraduates

I'm planning on getting into research in mathematical physics and was wondering about interesting topics I can get into and possibly make some progress on. I'm particularity fond of abstract algebra ...
7
votes
2answers
1k views

Hydrostatic friction: why do water droplets stay at rest on an inclined glass surface?

Tjis is a non-expert question on a (seemingly simple) text-book topic. The question is about "hydrostatic friction", defined as follows. Consider a drop of water resting on a flat surface. If the ...
6
votes
4answers
777 views

What is the physical definition of causality?

Maxwell's equations give a physical relationship between the electric and magnetic fields $\vec E$, $\vec B$ at the same time, which some interpret as changes in one causes changes in the other etc. I ...
4
votes
7answers
709 views

Most techologically applicable physics research area

Lets say you're an undergrad physics student with a lot of "sense" for technology and limited theoretical abilities. Now you need some kind of a career advice about the specific field of physics to ...
4
votes
7answers
800 views

What are the frameworks of physics?

Are there physical theories in use, which don't fit into the frameworks of either Thermodynamics, Classical Mechanics (including General Relativity and the notion of classical fields) or Quantum ...
4
votes
2answers
91 views

Does physics have some division schema which divide physical amounts into these two classes?

Does physics have some division schema which divide amounts into these two classes? : A) amounts which can be counted by natural numbers (for example many units can be counted by number of ...
4
votes
1answer
353 views

interpretation of Green function

Is there a physical interpretation of the existence of poles for a Green function? In particular how can we interpret the fact that a pole is purely real or purely imaginary? It's a general question ...
4
votes
3answers
2k views

Please recommend a good book about physics for young child (elementary school aged) [closed]

I'm looking for a book that would be appropriate for an advanced elementary school aged kids (say, 6-11 YO) describing the basics of physics (or sciences in general) in entertaining way. The ...
4
votes
1answer
1k views

Cooking pasta: why does adding a lid lead to overflow?

When cooking pasta, some organic foam usually forms on the surface of the boiling water and the situation can be kept under control by adjusting the heat (and/or adding some oil). Covering the pot ...
4
votes
4answers
2k views

Why the breath sometimes warm and sometimes cold? (2 different explanations!)

If you blow air against your hand with your mouth open, you feel warm breath. If you do with with your lips closed except for a small opening, you feel cold breath. One explanation from here says ...
4
votes
0answers
80 views

Can a discoverer give the name he wants to his finding? [migrated]

Let's assume that some scientist discovers a phenomenon that has never been noticed before. He wants to write a paper about it but he doesn't want to constantly write "effect of change of some ...
3
votes
3answers
373 views

Is there any physics behind flocking?

There are many articles published in physics journals about flocking. Is there a physical reason for these phenomena or is it just because physics methods are being used to study collective motion? ...
3
votes
1answer
402 views

Body's Electrical Resistance

I am not someone specialized on physics, I am just curious on why our Body Electrical Resistance measure as shown by a multimeter varies so much. When allocating the 2 probes each on one hand, the ...
3
votes
1answer
1k views

Why does the monitor make a cracking noise?

After switching off the monitor, there's a single crack after a while. I wonder where exactly it comes from. I know that this is normal and not an indicator of being defect. This sound is also not ...
3
votes
1answer
9k views

Is there any significance to 1.21 GW?

In connection with a related question on Science Fiction & Fantasy Stack Exchange page: does this number 1.21 GW make any sense? What is 1.21 GWatts? With what can you compare it? Can the ...
3
votes
1answer
686 views

Do quantum computers manufactured by D-Wave Systems, Inc. work? [duplicate]

D-wave claims to have built 128 qbit quantum computers which are commercially available? What I don't understand is that have they really been able to do this given that the scientific community is ...
2
votes
5answers
510 views

Why mathematical equations can describe this world? [closed]

Since I want to understand the world, I learn physics from textbooks. But I feel there is a gap between the textbook and the world. I do not know why the equations in the textbook can control the ...
2
votes
3answers
17k views

Uses of Vectors In Real Life

I always wonder how vectors are used in real life.Vectors and decomposition of vectors,dot and cross products are taught in the early stage in every undergraduate physics course and in every ...
2
votes
2answers
970 views

Why does a balloon spiral in air instead of moving in a straight line?

When an air-filled balloon is released without its opening tied up, it moves in a circular path rather than a straight line. Why is that? PS: I don't know what to tag this question as.
2
votes
1answer
137 views

Does physics address the topic of consciousness?

Does physics address the topic of consciousness? For instance, does physics say anything about how it might arise or what might be its qualitative properties? I'm wondering because it's interesting ...
2
votes
3answers
133 views

Can a theory be proven by an experiment (or series of) that sustains it?

This is a question that I've always had but it wasn't until the recent news regarding the BICEP2 experiment that I really gave thought about it (please note that the question is general and not ...
2
votes
2answers
141 views

What's the meaning of dimensionality?

I got amazed with this answer and as you can see, I had a little talk with joriki. He suggested me some examples such as the 2DEG. I'm stuck with some aspects on dimensionality, see this line: A ...
2
votes
3answers
467 views

What does physics study? [closed]

Wikipedia definition: Physics (from Ancient Greek: φύσις physis "nature") is a natural science that involves the study of matter[1] and its motion through spacetime, along with related concepts such ...
2
votes
1answer
666 views

How does a V formation save fuel for the lead plane?

I'm watching an episode of Mythbusters where they show aircraft saving 3-5% fuel when flying in a tight V formation. Interestingly, this also applies for the lead airplane. How is that possible for ...
2
votes
1answer
72 views

Question about two vehicles moving toward each other, but the answer doesn't seem correct, am I missing a key concept? [closed]

The problem statement Vehicle A and Vehicle B are moving in opposite directions on the NJTP. Vehicle A is heading south toward atlantic city while vehicle B is heading north towards Hoboken. In ...
2
votes
2answers
521 views

The meaning of 'postulate' in physics? [duplicate]

What does postulate mean in physics? What is its role in physical theories? Is it possible to break physical postulates?
1
vote
5answers
305 views

Age of universe estimates

I was recently involved in a discussion on a sister site regarding how tightly coupled Physics is with the age of the Universe (and Earth). I believe that the Earth and the Universe are both billions ...
1
vote
2answers
189 views

Publication Authorship Credits

Many physics papers now have dozens of authors per paper. Experimental physics may have multi-organizational and multi-country contributing staffs, but I'd guess that most of the names don't ...
1
vote
1answer
154 views

recommendation for a physics history/non-fiction book [closed]

I know that there are a lot theses being published on lives of physicists. Is there a history/non-fiction book that tracks the development of a problem chronologically? Like pieces of a puzzle. I ...
1
vote
2answers
214 views

Dragon Ball Z: Hyperbolic Time Chamber *(also increased gravity training) [closed]

Firstly, I am sorry if this seems like a joke. It is not. I have always loved the Dragon Ball series, so this question has been on my mind for a while. Can ...
1
vote
1answer
595 views

Power radiated by the sun at different locations

I am wondering can someone help to solve second part which extends first part; The power radiated by the sun is ${3.9*10^{26}}_{watt}$. The earth orbits the sun in a nearly circular orbit of radius ...
1
vote
1answer
100 views

Retarded field interaction

I was doing the following thought experiment: imagine a particle that moves at a certain velocity. Imagine also that the particle generates a field that propagates at velocity $v_f$. Well, if the ...
1
vote
1answer
102 views

Why is it that when you pick up a cup from a stack of solo cups too quickly, they stick together?

Intuitively I think it makes sense but can somebody explain very clearly to a non-physics person why it is that when you pick up a cup from a stack of solo cups very quickly, the cup below it seems to ...
1
vote
0answers
53 views

Is entropy a dynamical quantity [closed]

I am confused whether Entropy is a dynamical quantity or not. Gibbs entropy, and quantum mechanical Von Neumann entropy.
1
vote
0answers
245 views

Physics for Civil Engineering (Earthquakes, Materials Science for structures) or Fluid Mechanics? [closed]

I am currently a first year Ph.D. student in Applied Math. As an undergrad, I did not have the opportunity to take a calculus based physics course and the one I took was a general physics course where ...
1
vote
0answers
335 views

What are the biggest unanswered questions in physics today? [closed]

Are there fundamental big questions in physics that most scientists encounter no matter what they're working on, or are most questions details of smaller subtopics? What are the great unknowns of our ...
1
vote
0answers
123 views

Scales and Hooke's Law

Bob weighs $B$ kg and when he steps on a scale, the spring inside gets compressed by $c$ meters. Assuming the scale obeys Hooke's Law, if Alice weights $A$ kg, how much work is done compressing the ...
1
vote
0answers
98 views

Practical personal aircraft today? [closed]

Is it possible to build, today, a personal aircraft that not use an impracticable amount of fuel for everyday use? What are the physical concepts that could be used to build it?
0
votes
3answers
183 views

Do negative numbers have any physical meaning?

So, mindlessly wandering off into space, thinking about quantum and how cool physics is, I came to a realization that... well.. negative numbers to me make 0 sense. You have either something, or not ...
0
votes
2answers
338 views

General physics landau [duplicate]

I've found Landau 's book for a first course in physics (not theoretical physics, its title is general physics),the book is freely and legally avaible on archive.org ,but it's from 1967,is that ...
0
votes
2answers
132 views

Weight on planet earth?

I was wondering : does the weight on the planet earth is equal over the years ? meaning : all the people , ground , water ,gas. does the weight stays the same over the years ?
0
votes
2answers
559 views

Difference between pressure and stress tensor

What is the difference between hydrostatic pressure and stress tensor?