What is Constants: Definition and 486 Discussions

A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that is generally believed to be both universal in nature and have constant value in time. It is contrasted with a mathematical constant, which has a fixed numerical value, but does not directly involve any physical measurement.
There are many physical constants in science, some of the most widely recognized being the speed of light in vacuum c, the gravitational constant G, the Planck constant h, the electric constant ε0, and the elementary charge e. Physical constants can take many dimensional forms: the speed of light signifies a maximum speed for any object and its dimension is length divided by time; while the fine-structure constant α, which characterizes the strength of the electromagnetic interaction, is dimensionless.
The term fundamental physical constant is sometimes used to refer to universal-but-dimensioned physical constants such as those mentioned above. Increasingly, however, physicists only use fundamental physical constant for dimensionless physical constants, such as the fine-structure constant α.
Physical constant, as discussed here, should not be confused with other quantities called "constants", which are assumed to be constant in a given context without being fundamental, such as the "time constant" characteristic of a given system, or material constants (e.g., Madelung constant, electrical resistivity, and heat capacity).
Since May 2019, all of the SI base units have been defined in terms of physical constants. As a result, five constants: the speed of light in vacuum, c; the Planck constant, h; the elementary charge, e; the Avogadro constant, NA; and the Boltzmann constant, kB, have known exact numerical values when expressed in SI units. The first three of these constants are fundamental constants, whereas NA and kB are of a technical nature only: they do not describe any property of the universe, but instead only give a proportionality factor for defining the units used with large numbers of atomic-scale entities.

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  1. B

    Dimensions of three constants

    Homework Statement Consider a Rocket in space, far removed from external gravitational influences, and suppose the engine starts up. As long as the engines are running, its instantaneous velocity v is a function of its mass. V is given by: V = A + B log(D/m) A, B, D are physical...
  2. B

    What is the role of the phase constant in simple harmonic motion?

    Homework Statement How can I determine the phase constant of the these graphs? I am kind of confused about phase constant and its physical meaning, so if someone could explain it to me, I would be very grateful. Homework Equations The Attempt at a Solution
  3. A

    Linear combinations of structure constants

    I have two Lie algebras with structure constants f^{a}_{bc} and g^{a}_{bc}, the number of generators being the same (as will become clear). Due to a particular symmetry/construct, I have that the system needs to be valid under g \to af + bg (and a similar transform for g), which leads...
  4. C

    Detemination of dissociation constants of weak acid

    Procedure: 1. Pipette 25 cm3 of ethanoic acid into a conical flask 2. Titrate against 0.1M sodium hydroxide solution in the burrette, using phenolphthalein as indicator. 3. Pipette further 25 cm3 of ethanoic acid into the solution after titration and mix throughly. Questions: 1. what is...
  5. H

    Matter with different constants

    If the physical constants vary from universe to universe in a multiverse, then if matter from this universe were to somehow go into another universe, say through a wormhole, what would happen to it? Would it disintegrate, or somehow behave strangely? What if the cosmological constant varied in...
  6. K

    Spring Constants for bimetallic bars

    Hi all, Im a third year mechanical engineering student, starting on the topics of vibration analysis. Question: A rectangular prism bar is made up of two parts. The top layer is Steel(E=207E9 Pa) and the bottom layer is Aluminum(E=83E9 Pa). The bar is in axial motion. The dimensions are...
  7. T

    Constants in Lenard Jones Potential

    Does anybody know where I can find the value for the Lenard Jones potential constants (sometimes denotes as A and B, sometimes as Sigma and Gamma) for specific molecules and/or solids?
  8. X

    Finding the value of constants in f(x) as x->0

    I'm not looking for the complete answer (from what I've read in the intro posts, you won't/shouldn't give it to me anyways)... I just need to figure out where to start. This is my first time taking calc, and I'm pretty lost. Thanks in advance. Homework Statement Find the values of the...
  9. P

    RC Circuits and time constants

    RC Circuits! A capacitor in a single-loop RC circuit is charged to 63 % of its final voltage in 1.5 s. Find (a) the time constant for the circuit and (b) the percentage of the circuit's final voltage after 3.5 s. Given that V/Vo = 63%, t = 1.5 sec , Time constant =τ Now...
  10. marcus

    Only two fundamental constants? (Matsas in Nature News)

    http://www.nature.com/news/2007/071220/full/news.2007.389.html this just came out in Nature News, comment? To be sure, they are talking about how many DIMENSIONAL fundamental constants you need. The main bunch of constants that people always want to measure and to explain are the...
  11. H

    Fecund universes and physical constants

    How much water does Lee Smolin's theory of fecund universes hold? Also, according to his theory, the basic parameters of nature vary between universes. My question is - how much? Is it a noticeable difference that would make life as WE know it impossible?
  12. Jim Kata

    The constants of physics not constant

    I'm in a hurry so I'm going to say this quick. For angular momentum you have [J_i ,J_j ] = i\hbar \varepsilon _{ijk} J_k and for isospin you have [t_i,t_j] = ig\varepsilon_{ijk}t_k now, \hbar is viewed as a constant, but g is allowed to change it's value due to renormalization...
  13. D

    Can a Non-Linear Spring Constant Affect Projectile Motion Results?

    Hi all, I'm a physics teacher at an australian high school, and some kids that I teach have give me some interesting data reguarding spring constants. They made a contraption to project marbles as part of an analysis of projectile motion, and part of the contraption was a spring, used to...
  14. S

    Where do these constants in equations come from?

    Something I've always wondered: how did Physicists and Mathematicians of years past discover equations with these integer (and even fraction) constants in them? Take for example the mean-square-speed equation: \mu \equiv \sqrt{\frac{3RT}{M_{m}}} or Kinetic Energy: \frac{1}{2}mv^{2} How...
  15. A

    Solving Constants of Motion for Particle in 3D - No Quotes

    [SOLVED] Constants Of Motion A Particle of mass m moves in three dimensions under the action of a conservative force with potential energy V(r).Using the sperical coordinates r, \theta,\phi, obtain the hamiltonian function for the system. Show that P_{\phi} , \frac{P^{2}_{r}}{2m} +...
  16. L

    Solving Spring Tasks: Plotting Graphs and Calculating Spring Constants

    Homework Statement Preliminary questions: 1. John's weight is 618 N. He is sitting on a bosun's chair which is suspended from a spring. John's feet are pressing vertically down on a bathroom scale which reads 45 kg. What force is John exerting on the bathroom scale? Correct, computer...
  17. B

    Determining Constants in Equataions

    Homework Statement In all the following problems state the variables or combination of variables which should be plotted to check the suggested variation and state how the unknown may be found ( through the slope and/or intercept of the best fitting straight line y = m x + b.). Because...
  18. K

    Exploring Magnetic Forces: Net Field Effects & "Spring" Constants

    I've been digging around on the internet for information about magnets. I've found some interesting thing like the inverse square law of intensity, but I've noticed the Lorentz equations tend to deal mostly with charged particles. I'm really looking for information about the net field's...
  19. B

    Linear algebra - solve linear system with complex constants

    Solve the following linear system: ix + (1+i)y = i (1-i)x + y - iz = 1 iy + z = 1 I am getting nowhere with this. is there a trick to do these? I keep getting more and more variations of i. like i^2-1, and (1-i^2)-1 ix + (1+i)y=i (1-i)x + y-iz=1 y + z = 1 ix + (1+i)y = i i(1-i)x - (i^2-1)z =...
  20. T

    Strange physics question involving no constants and all variables.

    Homework Statement "K" is the time derivative of acceleration. Assume initial conditions of Ao, Vo, and Do.("o"=initial). Find: a(t): v(t): d(t): Show that: af^2=ao^2+2J(Vf-Vo) Homework Equations I'm honestly lost on this one..I don't know where to start. I could probably...
  21. P

    Evaluating Limits Involving Constants: A Step-by-Step Guide

    Homework Statement Evaluate the limits in the terms of the constants involved: \lim_{x \rightarrow a} \frac{(x+a)^2-4x^2}{x-a} Homework Equations The Attempt at a Solution First I plugged in a to make sure it was indeterminate and it was it ends up being 0/0. So I...
  22. N

    1st O.D.E, homogenous but with constants

    Homework Statement solve: y'=(x+y-1)/(x-y-2) i.e Homework Equations The Attempt at a Solution let y=vx thus y'=v'x+v by substitution: v'x+v=(1+y/x-1/x)/(1-y/x-2/x)=(1+v-1/x)/(1-v-2/x) v'x=(1-1/x+v^2+2v/x)/(1-v-2/x) still can't separate the variables...any...
  23. Loren Booda

    Mathematica Occurence of fundamental mathematical constants

    0, 1, phi (the Golden ratio), e, pi, delta (Feigenbaum's constant) and comparatively many other fundamental, dimensionless mathematical constants occur on the interval 0 to 5. With a potential infinity of numbers to choose from, why does such a confluence exist?
  24. A

    Which variables are constant in different types of projectile motion?

    Homework Statement For type 1, 2, or 3 projectiles, which of the following are constant? Dx, Dy, Vx, Vy Homework Equations The Attempt at a Solution I figure that the only one that is constant in all situations would be Vx because there is no acceleration in the x...
  25. tandoorichicken

    Spring Constant: Compression vs Extension

    Basic engineering question. For any average spring (say, in an industrial setting), is the spring constant in compression about equivalent to the spring constant in extension?
  26. P

    Normalisation constants in physics?

    Are normalisation constants in physics always real valued? If yes, is that because the normalisation constanst only normalises measureable quantities which are always real so the constants are real also. Any exceptions?
  27. T

    Time constants, resistance and RC circuits

    I just need some help understanding some of the theory behind these.. Can anybody help explain the relevance of a time constant in an RC circuit and why the time constant increases as resistance increases? Thanks in advance:blushing:
  28. A

    Searching for Dielectric Constants

    hi everybody...:cool: I'm looking for materials with dielectric constant 10,94 and 32,8... Please help me.. if you want to respect me, please send email to: alexz_lib3rty@yahoo.com Thanx...Gbu all
  29. S

    Finding Spring Constants: An Experiment

    Sorry i ditched the template but as this is an experimental question i wasnt sure that it was needed. FOr Physics i am currently writing up an experiment which i had to do i class, the experiment was based upon finding te spring constants of springs by hanging masses on them and measuring the...
  30. E

    List of fundamental equations and constants of the standard model

    Hi Is there anywhere a list of all constants (with their values) and fundamental equations (which can not be constructed from any other equations) of the standard model? thx einKI
  31. E

    Finding a landing speed from spring constants

    Homework Statement Problem: http://img147.imageshack.us/img147/8509/physjc9.gif Additional info: mass of the lander 7750 kg, 1.790967742 is the mag of acceleration due to gravity, this info was found in earlier parts of the problem Homework Equations I used these 2 equations and...
  32. C

    Calculating constants to high precision

    I'm trying to calculate some simple constants to high precision -- a few tens of millions of decimal places, maybe even a few hundred million. Are there any good programs out there that are fast at doing this? I'm using PARI/GP right now, but it's taking quadratic time to calculate ln(2)...
  33. A

    Two different thermal conductivity constants

    Homework Statement Solid cylindrical copper rod 0.2m long has one end maintained at temperature 20K, other end blackened and exposed to thermal radiation from surrounding walls at 500K. As the rod is insulated, no energy is lost or gained except at the ends of the rod. When equilibrium is...
  34. B

    Bragg equation to determine the lattice constants

    Does anyone have a link or know a website where there is a table of values of lattice constants for NaCl, LiF etc? I'm asking because I was supposed to be provided with a table of values for writing my lab report, but unfortunately the lecturer seemed to have got 'array'. Any help and...
  35. G

    QM constants from avg energy

    Hey, I have a normalized wave function PSI = c_1 psi_1(x) + c_2 psi_1(x) where c_1 and c_2 are constants with the eigenfunctions equal to ground and first excited state. The average energy of the system is pi^2hbar^2/(ma^2) - what can one deduce about the constant and how? Thanks...
  36. T

    Pogo Stick and Spring Constants

    http://img178.imageshack.us/img178/75/43802nv4.jpg A child's pogo stick (see figure) stores energy in a spring of spring constant k = 40000 N/m. At position A, x1 = -0.150 m, the spring compression is a maximum and the child is momentarily at rest. At position B, the spring is relaxed and the...
  37. S

    Radioactive decay equilibrium when decay constants are equal

    I need a refresher on calculus need to derive this equation, the question is: A --> B --> C and where decay constants: http://img183.imageshack.us/img183/4403/aki2.jpg Derive an expression for the activity of B as a function of time. So what I'm having trouble with is changing the...
  38. X

    Problem involving gravitational constants

    Hi all, I was just working on a problem involving gravitational constants like \frac{\Delta(g)}{g}. Anyway, its been awhile since I have been in my intro physics classes and forgot how to make approximations that allow the adding of large numbers with small numbers (in my case 9.80665 +...
  39. M

    Understanding the Importance of Constants in Proportional Formulas

    why should there is a 'constant' in a formula in which charactors on both sides are propotional to each other? and what should be the importance of it?:confused:
  40. A

    Line integral w/ constants only only in integrand

    Hello, I want help in the line integration of: Integral( 1 dy + 3 dx ), over the curve C. Where C is the union of two line segments: Line 1 from point (0,0) to (1, -3) Line 2 from point (1, -3) to (2,0) The thing is I do not know what to do with the integrand being composed of...
  41. M

    Structure constants of Lie algebra

    The following matrices are written in Matlab codes form. The standard basis for so(3) is: L1 = [0 0 0; 0 0 -1; 0 1 0], L2 = [0 0 1; 0 0 0; -1 0 0], L3 = [0 -1 0; 1 0 0; 0 0 0]. Since [L1, L2] = L3, the structure constants of this Lie algebra are C(12, 1) = C(12, 2) = 0, C(12, 3) = 1...
  42. M

    Structure constants of Lie algebra

    The following matrices are written in Matlab codes form. The standard basis for so(3) is: L1 = [0 0 0; 0 0 -1; 0 1 0], L2 = [0 0 1; 0 0 0; -1 0 0], L3 = [0 -1 0; 1 0 0; 0 0 0]. Since [L1, L2] = L3, the structure constants of this Lie algebra are C(12, 1) = C(12, 2) = 0, C(12, 3) = 1...
  43. S

    Variying constants and LQG

    Today someone has asked me about the evidences about the variations of fundamental constants (mainly alpha) As it is known that variation attemps versus the equivalence principle. So i wonder, if that variation would be irrefutably confirmed how would it affect LQG? I mean, LQG...
  44. T

    Dielectric Constants from solids to pellets

    Hi, Could someone explain why when comparing a materials dielectric constant in solid form it is sometimes higher in pellet form and sometimes lower for other materials. For example, Polypropylene has a dk = 1.5 when in a solid (lump) block. This then becomes dk ~ 1.5 - 1.8 when in pellet...
  45. A

    Dielectric Constants & Breakdown of Various Materials

    I need a huge table of the dielectric consant and breakdown of various materials... I have looked all over the net but can only find small tables with 5-10 materials...
  46. V

    Kinematics with an elevator that has 2 acceleration constants

    The Problem: A car is to be hoisted by elevator to the fourth floor of a parking garage, which is 48ft. above the ground. If the elevator can accelerate at 0.6 \frac{ft.}{s^2}, decelerate at 0.3 \frac{ft.}{s^2}, and reach a maximum speed of 8 \frac{ft.}{s}, determine the shortest time to make...
  47. C

    Ionisation Constants of HF & Its CB: Why 10-14?

    If 6.8 * 10-4 is ionisation constant(IC) of HF, what is the IC of its conjugate base. HF +H2O -----> H3O+ +F- So F- is the conjugate base(CB) I figured the IC of CB would be the reciprocal of IC of HF. But the answer given is the same but multiplied by Ionic product of water i.e. 10-14 Please...
  48. S

    Calculating Equilibrium Constants for Gas-Phase Reactions

    a. If the equilibrium concentration of AB3 is 1.5600 mol/L, and the equilibrium concentration of B2 is 0.3300 mol/L, determine the equilibrium constant for this reaction. 2AB3 (g) <-> A2 (g) + 3B2 (g) Well, K_c = [B2]^3[A2]/[AB3]^2 [B2] = 0.3300 M [AB3] = 1.5600 M [A2] = ? [A2]...
  49. G

    Solving a Math Problem with Constants and Limits: Find a and b

    Given a, b are constants and lim x approch 1, a root x+3 - b all over x-1 equals 1. Find a and b No clue how to answer this, but this is what I think i can do a) get rid of the sqrt b) apply limit See, the problem is I have to unknows so i don't know what to do
  50. G

    Calculus 1 (limits, VA and constants)

    Im in calculus 1 and need some help Question: Find the vertical asymptotes for… F(x) = x^3 + 8 / x^2 –4 I got a va of –2 F(x) = 2x/ sin2x I got a va of 1 Find the limit Lim tan^2 2x/ x^2 x-0 I got 4 as my answer Lim x^2 –4 / (x + 2 )^2 x- (-2) I got –4/0 = no limit...
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