# Tag Info

55

There is a non-subjective and quite mathematical approach to this question. First, we have the simple linear proportionalities that aren't really physical laws but just definitions of physical quantities. Why are different sensible measurable quantities usually in linear or power-law proportions will be further clarified later. An example is $F=ma$ (just ...

45

At the physics 101 level, you pretty much just have to accept this as an experimental fact. At the upper division or early grad school level, you'll be introduced to Noether's Theorem, and we can talk about the invariance of physical law under displacements in time. Really this just replaces one experimental fact (energy is conserved) with another (the ...

35

I think a very easy-to-understand answer is that we humans rig the game to make things easier for us. For example, we choose to express the volume of a sphere as a function of its radius because a sphere's radius is EASY for us to measure. We are lazy creatures: $$V_{sphere}=\frac{4}{3}\pi{R^3}$$ Now suppose over the course of human history, we instead ...

19

I'll bring in a less technical answer. Actually, even more dominant than integer exponents, is exponent 1, i.e., linear dependence between causes and effects. And often, exponent 2 comes from integrating this effect (i.e. kinetic energy), or multiplying two linear effects in which the same cause appears. Why linearity? Well, this is as easy as 1 and 1 is 2, ...

19

No, physics is not rigorous in the sense of mathematics. There are standards of rigor for experiments, but that is a different kind of thing entirely. That is not to say that physicists just wave their hands in their arguments [only sometimes ;) ], but rather that it does not come even close to a formal axiomatized foundation like in mathematics. Here's an ...

17

1.) Find something that interests you. The secret to learning is to do something you can be passionate about. For one person it may be building metal detectors (cicuits etc.) and another may be more interested in string theory or crystal physics. Explore your local library's physics section. 2.) Become competent in the area that interests you. Thomas ...

16

A simpler answer would be: units. For example, in $F = ma$ the unit of measurement for force would match the units of measurement for mass and acceleration. By definition, a Newton of force is a Kilogram of mass accelerated by a Meter per Square Second. There is no need to clutter the equation by defining a different unit to measure force that requires a ...

14

It works with a lot of body parts. It will work with a piece of wire too. This keys work at about 433 Mhz, a resonant Lamda/4 antenna is about 18 cm. Obviously the whole key is shorter, the antanna is not tuned for maximum power transmission. By bringing the key close to some conductive material, the power transmitted increases. A very recondite answer ...

11

You ask a very interesting question. The other answers here point at some fine examples and reasonable explanations. However, I think they only touch on the largest cause for your observation: the human factor. Assumption Most formulas in physics have integer exponents. No other answer really challenges this hypothesis. To have an irrefutable proof of ...

10

In most cases, the answer is: Because the creator of the formula wanted to express it in a simple way. E.g. in $F = ma$ we are defining the mass ($F/a$), as the property that matter has to offer resistance to acceleration when applied a particular force. In short, Newton chose to represent this model as simple as possible. We could use a different value ...

10

Just a note in addition to the advice being given here is this: ACTUALLY DO THE PROBLEMS. Like on pen and paper. Do not under any circumstances look at a solution and go "Oh yeah, I get this. Next!" That is absolute bull and what many, many people who attempt to self-study physics end up trying and why a lot of them fail. It is very easy to skip on the ...

10

Vectors are probably the most important tool to learn in all of physics and engineering. Some random examples: Classical Mechanics: Block sliding down a ramp: You need to calculate the force of gravity (a vector down), the normal force (a vector perpendicular to the ramp), and a friction force (a vector opposite the direction of motion). E&M: Electric ...

9

The learning time problem affects everybody, physics is intimidating because to learn it, you have to recapitulate the history, there's no underlying axiomatic system to deduce from. On 't Hooft's website, you will find a self-study guide put together for this purpose. It should get you started, and I don't think I can improve on 't Hooft. But if you know ...

9

You start by starting the process. It really doesn't matter all that much how you start, only that you start. Go to the library, look through some books, etc. At first, you'll find much of what you read opaque. But, in a short time, you'll start connecting some dots and then more and then more still. You'll revisit material that was initially ...

8

A friend sent this as his explanation and it seems quite satisfactory to me: For a balloon to fly in a straight line, the direction of the jet of expelled air would have to be in line with the balloon’s centre of mass and its centre of drag – the point where the forces resisting the balloon’s forward motion are symmetrical If these two centres don’t ...

8

The proposed partition of physics into Thermodynamics, Classical Mechanics, and Quantum Mechanics is quite arbitrary. To take just one conspicuous example, statistical mechanics does not fit, as it is the discipline that mediates between these three areas of physics. The Physics and Astronomy Classification Scheme (PACS) ...

8

I basically agree with Argus, though I take a slightly different perspective. Physicists try to explain the world by constructing mathematical models to approximate it. The phrase mathematical model can sound mysterious, but it just means an equation or equations that predict what's going to happen given some initial conditions. For example Newton's laws of ...

8

The math we use to describe the behavior of the world around us has two types of quantities: values and units. "3.4" is a value. "Meter" is a unit. There are extra rules that value-unit pairs have to follow in order for the results to have any physical meaning: Two value-unit pairs must have the same type of unit if they are added or subtracted, i.e., ...

7

A few more here: Fractional quantum hall effects: had heard that the large magnetic field is originally aimed to see the Wigner crystal effect, instead of testing quantum hall physics. Asymptotic freedom (QCD running couplings to small at high energy): from Wilczek's book Longing for the Harmonies,'' at that time David Gross originally aimed to prove ...

7

The bodies internal electrical resistance is quite low. Bodily fluids have enough ions (dissolved salts mainly) for the conductance to be high. The thin layer of skin provides almost all of the resistance. Once the skin resistance is overcome (by wetting, or for higher voltages arcing), the low internal resistance dominates. So for instance, how good a ...

7

This is obviously a very broad question, but here are a few thoughts that may be helpful. As dmckee points out in a comment, it's difficult to define consciousness. However, consciousness clearly requires computation, and computation is something that physics can address. There is a psychological arrow of time: we can remember the past but not the future. ...

6

The Stern-Gerlach Experiment: originally setting out to corroborate the Bohr-Sommerfield hypothesis that the direction of the angular momentum of an atom is quantized, it was eventually realized that the proper interpretation of the observations was as the first evidence of particle spin and that the electron is a spin-1/2 particle. The Spin-Statistics ...

6

Physics is usually not rigorous. But there is a branch of physics, called mathematical physics, in which physics is treated with full mathematical rigor. There everything begins with formally stated assumptions (axioms) from which everything else is rigorously deduced. In particular, there are fully rigorous treatments of phenomenological thermodynamics ...

6

The world is a very complicated place, so to understand it physicists use two strategies: use an approximation that simplifies the world study only a limited part of the world For example, to understand the motion of the solar system to pretty good accuracy you just need Newton's laws of motion and gravity, as learned by generations of schoolchildren. ...

6

If you make a cardboard tube, put this into the ballons nozzle and then let go you'll find the balloon goes in a mostly straight line. It probably won't go exactly straight because the balloon probably isn't exactly cylindrically symmetrical, but it will go a lot straighter than without the cardboard tube. I recall doing this in primary school long before ...

6

Depends on what you mean by "sense" for technology. Condensed matter physics is the obvious answer, but that's partly because there are more condensed matter physicists than any other sort (particle physics gets all the press, but the condensed matter division of the APS is the largest). A great many of those people are employed in industry, so it's an area ...

6

Like you, I want to self-teach myself physics, yet here I am still at around the same stage I was a few years back. Why? Because to learn physics effectively, I need to be immersed in it for days, weeks, months even years at a time. I also need to be coached by good teachers and peers that can steer me in the right direction, and prevent me from being lead ...

5

OK, this is for experimental high energy physics as I worked in the field for over 40 years. There are groups in institutions, universities and research ones. There are many such in each country, and there are many countries. The group leaders in the group decide who signs a paper, mainly by the man hours put in the construction and running of the ...

5

This doesn't match your stated interests, but the things you talk about are generally well established fields with an enormous history, and it generally takes longer to get to the forefront of research in such areas. If you can code, there is the interesting problem of classical turbulence. It is wide open as mathematics and as physics, and there is a ...

5

The pole of Green's function is related to the spectrum of the particle which is propagating. One dimension for example $$\tilde{G}(\omega)= \frac{i}{\omega-(\epsilon+i\Gamma)}$$ If pure real, G(t) is some oscillation function which shows that the particle is stable. If pure imaginary, G(t) has some exponential decay behavior which shows that the particle is ...

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