Law Definition and 999 Threads

Law is a system of rules created and enforced through social or governmental institutions to regulate behavior, with its precise definition a matter of longstanding debate. It has been variously described as a science and the art of justice. State-enforced laws can be made by a group legislature or by a single legislator, resulting in statutes; by the executive through decrees and regulations; or established by judges through precedent, usually in common law jurisdictions. Private individuals may create legally binding contracts, including arbitration agreements that adopt alternative ways of resolving disputes to standard court litigation. The creation of laws themselves may be influenced by a constitution, written or tacit, and the rights encoded therein. The law shapes politics, economics, history and society in various ways and serves as a mediator of relations between people.
Legal systems vary between countries, with their differences analysed in comparative law. In civil law jurisdictions, a legislature or other central body codifies and consolidates the law. In common law systems, judges make binding case law through precedent, although on occasion this may be overturned by a higher court or the legislature. Historically, religious law influenced secular matters, and is still used in some religious communities. Sharia law based on Islamic principles is used as the primary legal system in several countries, including Iran and Saudi Arabia.Law's scope can be divided into two domains. Public law concerns government and society, including constitutional law, administrative law, and criminal law. Private law deals with legal disputes between individuals and/or organisations in areas such as contracts, property, torts/delicts and commercial law. This distinction is stronger in civil law countries, particularly those with a separate system of administrative courts; by contrast, the public-private law divide is less pronounced in common law jurisdictions.Law provides a source of scholarly inquiry into legal history, philosophy, economic analysis and sociology. Law also raises important and complex issues concerning equality, fairness, and justice.

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  1. J

    Is there a conflict between CPT symmetry and the 2nd law of thermodynamics?

    Naively there is a conflict between CPT symmetry being at heart of fundamental physics models like QFT, and 2nd law of thermodynamics: saying that entropy grows toward future. Is there really a conflict here - so is physics symmetric or not? How to understand it? Personally I disagree with that...
  2. J

    How Long to Achieve Uniform Mixture in Helium Gas Experiment?

    This is an experiment on a dilute isotopic mixture of helium gas. A spherical vessel of diameter 1 m is first filled with 4He gas to one atmosphere pressure. Then a small amount of 3He gas is introduced through a valve on one side of the vessel. Make a rough estimate of how long one must wait...
  3. AHSAN MUJTABA

    Cosmology: Hubble's law and Redshift

    I tried to attempt this by taking z=dv/c but I saw that relation Liddle's book on Cosmology and I really don't know where this came from. Secondly, I will need some series ( maybe Bionomial) in terms of z from which I can show small z. I think it's simple but here it's not clicking to me.
  4. G

    I Problem about the usage of Gauss' law involving the curl of a B field

    I am trying to derive that $$\nabla \times B=\mu_0 J$$ First the derivation starts with the electric field $$dS=rsin\varphi d\theta r d\varphi $$ $$ \iint\limits_S E \cdot dS = \frac{q}{4 \pi \varepsilon_0} \iint\limits_S \frac{r}{|r|^3} \cdot dS $$...
  5. jaumzaum

    Is Newton's third law valid for rotation / Torque?

    Is third Newton law valid for rotation / Torque? I mean, can we say that for every torque there must be another torque with equal magnitude and opposite direction? This can only be true for contact forces or radial forces, as these forces will create a reaction that will cancel the torque...
  6. Y

    I How Gauss’ Law is applied to cylinders

    If I understand correctly, Gauss’ Law is (roughly) derived as follows: Part A Electric Flux = EA E = q / (∈4πr^2) A of the surface of a sphere is 4πr^2 They cancel out and therefore EA =q/∈ Line 4 seems to only apply to a sphere, as it is based on line 3. Now, Gauss’ Law is applied to...
  7. L

    Engineering Why is the first law of thermodynamics useful in developing these equations?

    why it is first law of thermodynamics useful in developing the non-flow energy equation and steady-flow energy equation. First Law Equation (FLE) = 1 1.1 Non-Flow Equation = 2 Steady-Flow Equation = 3 Specific Entrapy of Steady-Flow 4 Mass Flow 5 I understand (i think) but can't explain...
  8. S

    Checking Kirchhoff's current law

    Im trying to apply KCL to the serial c and parallel rl circuit. IZ = = = 330.562 mA but this means incorrect proof. Anyone can help please?
  9. patric44

    Derivation of the Child-Langmuir law?

    hi guys i was trying to understand the derivation of the child Langmuir law that govern the current flow between the two plates of vacuum tubes and saw this derivation online : and i am stuck at couple of points : when i saw the derivation it seem like a direct application of the Poisson's...
  10. D

    Engineering Kirchoff's voltage law applied to this circuit with three loops

    I'm stuck straight out of the gate any help is really appreciated
  11. Andrei0408

    Understanding Exercise 3 and 8 in Freefall and Motion Law

    I need help with the exercises attached in the pictures. Basically, exercise 3 is already solved but I need some help understanding every subpoint (for example, at a) how did we get to 0=H -g* tAO/2 , I know it's from the motion law and vA=0, but why is y(t)=0?). And I tried solving ex 8, but I...
  12. Gaby

    The first law of thermodynamics for open systems

    Please see enclosed my calculations for parts 1-3. I am stuck on the final part of of a 4 part question, any help or guidance would be very much appreciated, thanks.
  13. P

    Coulomb's Law and Conditional Convergent Alternating Harmonic Series

    Mary Boas attempts to explain this by pointing out that the situation cannot arise because charges will have to be placed individually, and in an order, and that order would represent the order we sum in. That at any point the unplaced infinite charges would form an infinite divergent series...
  14. mcastillo356

    First law of Thermodynamics and energy conservation

    Hi PF! I don't understand the sentence: on one side says the energy is preserved, and, at the end, the total energy of the system will change if ##W## or ##Q## is added: ##\Delta{U}=Q+W##. Greetings!
  15. mingyz0403

    Engineering Newton’s Second Law of Motion — Collar sliding on a rotating rod

    The soultion used polar corrdinates. Acceleration in polar corrdinates have radial and transeverse components.When calculating the acceleration of collar respect to the rod, the solution only calculates the radial component of acceleration. Is it because the collar is on the rod, so the...
  16. E

    "Where’s your second law of thermodynamics now?"

    Prof. Tong used the Liouville theorem to prove the Poincaré recurrence theorem in his notes, that given an initial point ##P## in phase space, for any neighbourhood ##D_0## of ##P## there exists a point ##P' \in D_0## that will return to ##D_0## in a finite time. To illustrate the theorem, he...
  17. Twigg

    Kelvin-Planck 2nd Law of Thermo & a Syringe Steam Engine

    So I found this steam engine on the youtubes: Consider the system not including the candles, only including the can that makes up the boiler shell and the piston, flywheel, etc. The boiler can acts as a hot reservoir; however, the Kelvin-Planck statement of the 2nd law says you can't have an...
  18. K

    Proof question related to the Ideal Gas Law

    A cylinder contains an initial volume V1 = 1m^^3 of a perfect gas at initial pressure p1 = 1 bar, confined by a piston that is held in place by a spring. The gas is heated until its volume is doubled and the final pressure is 5 bar. Assuming that the mass of the piston is negligible and that the...
  19. R

    The violation of Newton's third Law

    Let us consider two point charges: one of which moves (in the simplest case) rectilinearly with a constant speed and the other is at rest. The electric field of the first charge is renormalized due to the effects of retardation and generation of a solenoidal electric field (see Am. J. Phys...
  20. K

    Comp Sci Need help finding the resistor size for a circuit (Ohm's law)

    I know there is a serial and parallel circuit I know R1 = 2k, R3 = 1k and i know Vout which is 1V. And i know 5V is coming from supply. I need to calculate the size of resistor R2. I can calculate : 1) IR1 = 5-1V/2000ohms = 2mA 2) UR1 = 0,002A*2000ohms=4V voltage drop on R1 How do i go on...
  21. M

    First Law for a Eulerian non-inertial system

    Hello to everyone, I'm trying to demonstrate (a) starting from a Lagrangian system. However I have found some difficoulties so I hope you can help me. First of all, I'm going to illustrate a demonstration I found of the First Law, for a Eulerian -inertial system...
  22. Tony Hau

    Problems understanding the 2nd law of thermodynamics

    So my professor says that the implication of 2nd law of thermodynamics is that high quality energy will be degraded into low quality energy. By high quality energy he means something like coal or fuel. By low quality energy he means something like heat entering the cold resevoir in a heat...
  23. M

    Three positive point charges are located on a line (Coulomb's Law)

    I need some help resolving the follow problem. I really don't know where to put the "twice as large as the resultant force on Q3" in order to build an equation. Thank you !
  24. cwill53

    Using the solid angle to simplify an integral when deriving Gauss' Law

    I'm a bit confused on the derivation above. I understand what the goal of the derivation is, as it derives Gauss's Law using the solid angle, but i was wondering if someone could kind of fill in the steps the author skipped and explain the use of the solid angle.
  25. E

    A better way of proving the Weiss Zone Law?

    For some context, a Bravais lattice in 3D is described by 3 basis vectors ##\vec{a}_1##, ##\vec{a}_2##, ##\vec{a}_3## s.t. a discrete point in the lattice can be generated with ##\vec{R} = \sum R_i \vec{a}_i##, with ##R_1##, ##R_2##, ##R_3## being integers. A direction is specified by a triplet...
  26. J

    Chemistry Ideal Gas Law and Partial Pressures

    I had already found the Mass of the product (C3H3N) produced by this reaction (theoretical mass at 100% yield) in a previous problem. I did this by finding the Limiting Reagent (C3H6) in the reaction , calculating the number of moles of C3H6 and using the Molar Ratios in the balanced reaction...
  27. wcjy

    Electric field problem using Gauss' law: Point charge moving near a line charge

    F = qE ma = (2*10^-6) * (λ / (2pi*r*ε0) ) ma = (2*10^-6) * (4*10^-6 / (2pi*4*ε0) ) => I am not certain what to put for r ( But I sub in 4 because dist is 4) a = ( (2*10^-6) * (4*10^-6 / (2pi*4*ε0) ) )/ 0.1 a = 0.35950 v^2 = U^2 + 2 a s v = 0 u^2 = -2 a s => Can't sqrt negative so...
  28. E

    Pulley and Two Masses -- Newton's Law of Motion

    From this question, I do not understand why there are three forces exerted at Point C (2 of it being the tension by weight A and the other is the tension by weight B) I understand that there is tension by the two weights but why is there 2 forces exerted by weight A at point C? From the...
  29. M

    Engineering First law of a thermodynamic system

    After crossing out all the variables which I think equals 0 in the equation, I was left with: ∆PE + ∆U = Qin mg (0.2) + ∆U = 300 10*9.81*0.2 - 300 = - ∆U = -280J This was the answer I derived. However, the correct answer was supposed to be 123.3J. Please can someone explain to me how to get...
  30. WMDhamnekar

    MHB Exploring Robert Boyle's Law: Pressure and Volume of CO2

    Robert Boyle's law states that at constant temperature, the pressure of fixed amount ( i-e number of moles n) of gas varies inversely with its volume. Mathematically, it can be written as $p ∝ \frac1V $(at constant T and n) $\Rightarrow p = k_1 \times \frac1V $ where $k_1$is a proportionality...
  31. D

    Solving Transcendental in Wien's Displacement law

    Hello, I have attached my attempt at a solution. All is okay until i reach x=5-5e^-x. My assignment suggests that i solve it by substituting x=5-ε into the equation where ε is assumed to be small. Solve for ε and then solved for x (Approximate). Thank you for your help
  32. Frigus

    B How to apply Lenz' law if we don't know what to oppose?

    In this question I can't understand how the loop is opposing the change in flux, I can solve it by simply imagining a bar magnetic with south pole pointing outwards placed inside the plane of image but how do I know that it is the same case as that of bar magnet? What if their is a case in...
  33. zb23

    Ampere's Law & Biot-Savart: Dealing with Infinity

    How to lose surface integral in derivation of ampere law from biot-savart law if current goes to infinity? How does current that goes to infinity obey Helmholtz theorem for vector fields?
  34. A

    B How does the weight on a scale change when an object is submerged in water?

    Dear, I am a medical doctor and my physics background is limited to that of secondary school many years ago, but should want to ask for your help. In attachment, you can find a picture of my question. On a scale, we place a jar filled with water. We place in the water a platform which is...
  35. R

    Using Gauss' Law to find the field at a point

    Attached is problem 23.03 from Halliday and Resnick. We have a sphere of uniform negative charge Q = -16e and radius R = 10cm. at the center of the sphere is a positively charged particle with charge q = +5e. We are supposed to use Gauss' law to find the magnitude of the electric field at...
  36. U

    Chemistry Calculating Mass Percentage of N2H4 in Hydrogen/Nitrogen Mixtures

    So essentially you are supposed to find the mass percentage of N2H4 in the Hydrogen/Nitrogen mixtures. The way I understood it, the only way to find the mass percentage of the gasses is to find the mole percentage. Which I got as 25%, based on the fact that the ratio of product gasses to...
  37. patric44

    Question about the nonlinear Hooke's law

    hi guys i saw this problem online about using the MATLAB ode45 to solve the nonlinear Hoock's law and its specifically stated that the nonlinear hoock's law is given by $$F = k\;u + \epsilon\;u^{3}$$ , but when expanding the potential function in a Taylor series where you obtain the force...
  38. M

    How to Derive the Conservation Law for the FRW Metric?

    My attempt: Realize we can work in whatever coordinate system we want, therefore we might as well work in the rest frame of the fluid. In this case ##u^a=(c,\vec{0})##. The conservation law reads ##\nabla^a T_{ab}=0##. Let us pick the Levi-Civita connection so that we don't have to worry about...
  39. Hamiltonian

    First law of thermodynamics and the work done on a system

    The first law of thermodynamics states that the change in the internal energy of a system equals the net heat transfer into the system minus the net work done by the system. In equation form, the first law of thermodynamics is ΔU = Q − W. in the mathematical expression of the first law of...
  40. AN630078

    Intensity of Stars and the Inverse Square Law Problem

    1. speed of light = 3*10^8 ms^-1 length of an Earth year=365 days*24 hours*60minutes*60seconds=3.15*1 0^7 seconds distance=speed*time 1 light year= 3*10^8 *3.15*10^7=9.46*10^15m 4.2 light years = 4.2*9.46*10^15m=3.9732*10^16m ~ 3.97*10^16m (to 3sf) 2. Intensity=power/area Power=1.4MW=1,400,000...
  41. T

    Can the charge conservation law be derived from Maxwell equations?

    From Maxwell's equations \partial_\nu F^{\mu\nu}=J^{\mu}, one can derive charge conservation. The derivation is 0\equiv \partial_\mu \partial_\nu F^{\mu\nu}= \partial_\mu J^{\mu} { \Rightarrow}\partial_\mu J^{\mu}=0. However, a circular reasoning exists in it. For the sake of better...
  42. brotherbobby

    Understanding Pascal's Law: Why is Force Greater in One Cylinder Than the Other?

    Answer : Using Pascal's law, this is my answer : ##\color{blue}{\boxed{\vec F_a = \vec F_c < \vec F_b}}##. Reasoning : Forces ##F_a## and ##F_c## are equal because the pressures required at the two cylinders for case (c) is the same as that required in (a). It doesn't matter how many of those...
  43. Nicolas01

    Lenz law how to find dA/dT and O?

    Hello, I am new and I have a question about the lenz law. How I am suppose to find DA/dt and o in this problem? A= 9 but D(9)/dt is equal to 0 ? And I don't really know what is the angle o means in this formula. If I found the voltage i can find the current with I= eps/Req .
  44. T

    Solving Newton's 2nd Law for Particle Falling in Medium

    Good afternoon, I have a question regarding this derivation that I'm covering in Thornton & Marion's "Classical Dynamics of Particles and Systems". In it, we're covering the most basic equation of motion for a particle falling in a medium. I understand the process of starting with Newton's 2nd...
  45. H

    B Newton's experimental law -- Questions about the collision of two spheres

    The following is from the 2018 AQA AS Further Maths/Mechanics Paper 2 exam: 'Two smooth spheres A and B of equal radius are free to move on a smooth horizontal surface. The masses of A and B are m and 4m respectively. The coefficient of restitution between the spheres is e. The spheres are...
  46. xyz_1965

    MHB Why is the Law of Tangent rarely used or taught in typical trigonometry courses?

    The next chapter in my personal studies is Law of Sines and Law of Cosines. I am not there yet. I know there is a Law of Tangent but it is rarely used and never taught in a typical trig course anywhere. Why is the Law of Tangent ignored?
  47. M

    Is the Second Law of Thermodynamics Falsifiable?

    My question relates to whether the 2nd law of thermodynamics is a an empirical or mathematical law. If we can reason purely from the laws of statistics that entropy can only increase, then the 2nd law of thermodynamics cannot be falsifiable and therefore shouldn't be considered a scientific...
  48. Jiman

    Is the principal of superposition of forces a part of the second law?

    The three laws are basic principles in Newtonian Mechanics. The principle of superposition of forces is part of the second law.But before we make the assumption of superposition of forces,we have to make another assumption which is the principal of superposition of motion.why are...
  49. A

    What is the -1st law of thermodynamics?

    The so called -1st (Minus First) law of thermodynamics, I believe states that information cannot be destroyed, or something along those lines. Does anyone know where I can read more about it? I think I've heard Dr. Leonard Susskind talk about it but it's been hard to find the video or any other...
  50. gumthakka

    Cases when Ampere's circuital law fails to hold

    Well, I guess that is pretty much my question.
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