Constant Definition and 1000 Threads

  1. Arman777

    I Why the speed of light is constant for every observer?

    Why the speed of light is constant for every observer ? Is it a special thing for photons cause I guess there's no other elementry particle that can move with c ? Also I want to investigate the constant of c for every observer, in the perspective of particle relationship. For example, can I...
  2. M

    Is there work for object moving at a constant speed?

    Homework Statement An object of mass 100kg is acted on by a constant force as it moves through a displacement at a constant speed of 7.2m/s. What is the net work done on the object? Homework Equations Wnet = ΔK Fnet = 0 The Attempt at a Solution I know that the answer is zero because the...
  3. L

    Constant acceleration except time?

    Homework Statement Homework Equations d = vit + 1/2at^2 The Attempt at a Solution Hey, so what i did was different from the answer key above. Instead of (4/5)^2 i did 1/ (4/5^2) so i got 25/16 as the answer. I'm not sure why tb/ta = 4/5 since 4/5 the time is referring to runner b's time...
  4. Edwin1974

    MHB Need help with reversal of a calculation involving gravitational constant.

    Hi. I would like to know if it is possible to "reverse engineer" the formula below to find (G) if Ve, M and r are all known values. Ve = sqrt{2GM/r} Ve would be escape velocity, G would be gravitational constant, M would be mass of planet and r would be radius of planet. I hope I am...
  5. R

    I Understanding the Constant of Integration in RL Circuit Equations

    I am having problem on understanding the below solution regarding constant of integration. On integrating an differential equation of RL circuit , for e.g $$10i + 3\frac{di}{dt} = 50 $$ $$i.e \frac{di}{50-10i} =\frac{dt}{3}$$ Integrate $$\frac{1}{10} \int\frac{1}{5-i} di = \frac{1}{3}∫dt...
  6. B

    Adding a constant to potential energy doesn't change action?

    Hello. I've been watching Susskind's online Stanford lectures on classical mechanics to review the subject, and I believe he said that adding a constant to the potential energy does not change the action of a system. I see how it doesn't change the Euler-Lagrange equations and therefore...
  7. karush

    MHB 243.13.01.19 For which path is the particle's speed constant

    $\tiny{243.13.01.19}$ $\textsf{The following equations each describe the motion of a particle.}$ $\textsf{ For which path is the particle's speed constant?}$ \begin{align*} \displaystyle R_1(t)&= t^7\textbf{i}+t^4\textbf{j}\\ R_2(t)&= \cos(3t)\textbf{i}+\sin(8t)\textbf{j}\\ R_3(t)&=...
  8. Ranku

    I Cosmological constant and rate of expansion of the universe

    Does the presence of the cosmological constant modify the rate of expansion of the universe even during the earlier deceleratingly expanding phase of the universe?
  9. binbagsss

    GR: find covariantly constant vector on a given curve

    Homework Statement I am stuck on finding ##W^u## Homework Equations [/B] I have computed the christoffel symbols via comparing the Euler-Lagrange equations to the form expected from geodesic equation. geodesic equation: ##\ddot{x^a}+\Gamma^a_{bc}\dot{x^b}\dot{x^c}=0## covariantly constant...
  10. M

    MHB What Determines the Time Dependent Value of A[t] in Quasi-Static Approximations?

    Hello, I'm working on my bachelor's thesis, and I ran into a problem. In the text they say: "For hot oil/watering jobs, U is typically large enough that f(t) is closer to a constant temperature than constant flux boundary condition. In the quasi-static approximation, these integrals are solved...
  11. ohwilleke

    I Is there a fine structure constant running anomaly?

    Background The chart above, via Lubos Motl's blog which is standard in any textbook talking about supersymmetry, illustrates the running of the the inverse of the Standard Model (SM) and Minimal Supersymmetric Model (MSSM) coupling constants with energy scale for the electromagnetic force...
  12. F

    Constant rotational kinetic energy

    A mass m is attached at the end of the string. The mass moves on a frictionless table, and the string passes through a hole in the table, under which someone is pulling on the string to make it taut at all times. Initially , the mass moves in a circle, with kinetic energy [E][/0] . The string is...
  13. J

    Constant acceleration and radius of curvature

    Homework Statement Homework Equations The Attempt at a Solution The normal acceleration of the particle at any instant is given by an = v2/r . v is the speed at any time and r is the radius of curvature . Minimum radius will occur when ratio v2/an is minimum . I think this will occur when...
  14. P

    Pushing spring from both sides - Find the spring constant

    Homework Statement A spring relaxed length is 0.5[m]. It is being pushed from both sides, and contracted to 0.4[m]. The force the spring is applying outwards is 3[N] on each side. What is the spring constant k? Homework EquationsThe Attempt at a Solution I attempted drawing a force diagram...
  15. D

    I Multiplying a wavefunction by a constant number

    Hi. Is the wavefunction for x≤0 , ψ(x) = sinkx - acoskx equivalent to ψ(x) = -sinkx - acoskx where a is a constant ? Thanks
  16. cnh1995

    Is synchronous reactance constant?

    In electrical machinery and power systems, the synchronous reactance is treated as a constant reactance in series with the generated emf and is independent of load condition. These threads were very helpful for me in understanding this concept (thanks to @jim hardy!)...
  17. C

    Equilibrium constant expression; why exponents?

    Hello all. I am wondering why we raise the concentration to the exponent of the stochiometric coefficient. I understand why we take the products of reactants or products. For instance, let me give an example to show where I am getting mixed up. Let's say 2A +3B = 8C as a reversible...
  18. D

    Quantum constant of motion in a magnetic field

    Hello, I have a doubt about the Complete Set of commuting observables (CSCO) in the cases when there are a magnetic field ##B## in z. The statement is find the constant of motion and CSCO for a particle of mass m and spin 1/2, not necessary a electron or any atomic particle. I know that the...
  19. EastWindBreaks

    Which side should I put constant C on?

    Homework Statement the second solution is the correct, I know you can put C on both sides and it simplifed to C2 on one side, but why can't you put C2 on the right side? Homework EquationsThe Attempt at a Solution
  20. T

    I Is the fine structure constant the biggest myth ever?

    The fine structure constant ##\alpha## is commonly cited as a very important quantity, because it gives the strengh coupling of the electromagnetic force. But it seems that the fine structure constant is not actually constant. It rather changes with the momentum of the (mediating?) particle and...
  21. EastWindBreaks

    How to find internal energy with constant temperature?

    Homework Statement since specific heat c changes with temperature, but its treated as a constant in the heat formula, so that means that heat formula Q=mc(T2-T1) is just an approximation? correct? I see some texts define heat as Heat, q, is thermal energy transferred from a hotter system to a...
  22. EastWindBreaks

    How to find internal energy with constant temperature?

    since specific heat c changes with temperature, but its treated as a constant in the heat formula, so that means that heat formula Q=mc(T2-T1) is just an approximation? correct? I see some texts define heat as Heat, q, is thermal energy transferred from a hotter system to a cooler system that...
  23. G

    Is gravitational constant unchanging over age of universe?

    do we know for a fact that the gravitational constant has always been the same since the dawn of the universe? I feel like gravitational forces should slowly be decreasing as the universe ages (meaning that assuming mass of Earth doesn't change, we should weigh a bit less in a billion years)...
  24. D

    Courses Is Constant Leap-Frogging Through a Text Normal?

    In my current math class, we are constantly leap frogging throughout the text. In week 1, we did a couple things from chapter 6, not going through it fully- just a few sections here and there. In week 2, we went to chapter 3, again only doing a couple sections somewhere in the middle of the...
  25. H

    Capacitor circuit time constant problem

    Homework Statement How long does it take in time constants ( = RC) for the charge on the capacitor in the circuit shown below to reach one quarter its initial value? Homework Equations C=Q/V time constant=RC Vc = Vo * (e)^(-t/RC) The Attempt at a Solution From C=Q/V I get Q=VC so for the...
  26. J

    Applied force compared friction force at constant velocity

    Homework Statement How does an applied force and a frictional force compare when moving at constant velocity? Homework EquationsThe Attempt at a Solution
  27. S

    100% energy efficient, constant power rocket

    I gather rocket energy efficiency is maximal when exhaust speed closely matches the rocket speed (but oppositely directed), so to an outside observer such a rocket would leave a stationary propellant trail. I’ve found little on this model and am trying to learn more. Say we have a rocket of...
  28. T

    Constant thickness lens varying refractive index

    Homework Statement Homework EquationsThe Attempt at a Solution my initial approach was to just imagine the light rays leaving the focal point and emerging parrallel but then the result had no dependence on thickness how to tackle this problem how does the thickness even factor in
  29. N

    Using Ideal and Constant Voltage Drop Models

    Homework Statement I am practicing diode circuit analysis for an ideal diode model and constant voltage drop model.I have an initial circuit shown here: Which I then redraw to look like this: I want to make sure my process in redrawing this was correct. When I attempt to get current through...
  30. W

    (Spring constant) I can't figure out what I did wrong.

    Homework Statement Two springs which have spring constant of k1 and k2 respectively are vertically hung in a series. Then, a mass m is attached to the end. Find the displacement and the spring constant of this series. Homework EquationsThe Attempt at a Solution I got the displacement x1+x2...
  31. Eclair_de_XII

    I got bored and did something with the dielectric constant

    Homework Statement I want to prove or disprove that the dielectric constant ##K## is the projection of ##\vec E_0## onto ##\vec E## using linear algebra. Homework Equations ##\vec E = \frac{\vec E_0}{K}## The Attempt at a Solution ##(\vec E)⋅\vec E = (\vec E)⋅\frac{\vec E_0}{K}## ##K(\vec...
  32. Y

    MHB Differentiating wrt constant to evaluate integral

    What is the justification for differentiating some integrals with respect to constants in order to obtain result, i.e. ∂/∂a[∫e^(− ax^2).dx] =∫-x^2.e^(-ax^2) dx?I mean what if we say "a" was 3 then differentiating wrt 3 would have no significance?How can we treat it like a multivariable function :/
  33. yecko

    Specific heat at constant pressure formula help

    Homework Statement https://i.imgur.com/f2vSXtq.png Homework Equations https://i.imgur.com/Kjy1Tzh.png The Attempt at a Solution In this question, the pressure is different at different point, in other words it is not constant throughout the system. Why the solution use c(p) (or "enthalpy" h...
  34. A

    Positive or negative final velocity? Constant acceleration

    Homework Statement A car is moving with a constant velocity of 18 m/s for 5 seconds, if in the next 5 seconds it travels a distance of 40 m, what is its final velocity? Homework Equations Δx= vit+ 1/2 at^2 vf= vi+at vf^2 = vi^2 + 2a (Δx) The Attempt at a Solution So I tried doing it different...
  35. L

    If a constant number h of fish are harvested from a fishery

    Hi! Can anyone help me? If a constant number h of fish are harvested from a fishery per unit time, then a model for the population P(t) of the fishery at time t is given by: dP/dt = P(5-P) - h, P(0) = P0. a. Solve for the IVP if h = 4. b. Determine the value of P0 such that the fish...
  36. HRubss

    How Long Does It Take a Car to Overtake a Truck?

    Homework Statement A car, length 2.4m, traveling at 26m/s wants to pass a large truck, length 12m, also traveling at 26m/s. If the car can accelerate at 4.4m/s2, how much time will it take the car to pass the truck (note the back of the car has to be in front of the truck)? How far will the car...
  37. S

    Constant acceleration changes direction twice

    Hello, I just did a practice physics problem that asked if an object with constant acceleration can change direction twice. The answer was no. What if you had an object attached to a string spinning at constant velocity. Is the tangential acceleration constant?
  38. ESMAT 1995

    Constant current source Inverter

    i was reading about CSI and the first paragaph said "A constant current source is assumed here, which may be realized by using an inductance of suitable value, which must be high, in series with the current limited dc voltage source. " and it says nothing else about it , so clearly it's a basic...
  39. A

    I Constant particle motion due to zero-point energy....

    Hi all, Just a clarification to ask about: if a have an electron (all by its lonesome) in its ground state, it will have non-zero kinetic energy (zero-point energy), even at absolute zero. This should mean the particle (oscillating field excitation in QFT) is always moving. Now, to be clear...
  40. RJLiberator

    Thermodynamics of a Constant Volume Gas Thermometer

    Homework Statement A constant volume gas thermometer contains a gas whose equation of state is (p+\frac{a}{V^2_m})(V_m-b)=RT and another, of identical construction, contains a different gas which obeys the ideal gas law, pV_m = RT. The thermometers are calibrated at the ice and steam points...
  41. J

    Why does my experimental value of g differ greatly?

    Homework Statement Hi, I did an experiment where I launched a soccer ball into projectile motion with my hand and took a video the situation. I uploaded it into the Tracker software to analyze it. The tracker software gave me a x-t graph, a y-t graph, and a y-x graph. From the y-t graph...
  42. romsofia

    I Why Is the Derivative of the Function Set as a Constant in Classical Dynamics?

    Hey, I am going to be a TA for an upper division classical mechanics class, and I'm going through the book, and making sure I can derive, or be able to justify equations used in the book. So far it has been okay, but one equation I can't justify. I will post the derivation here (or for those who...
  43. J

    Constant velocity, constant acceleration?

    Homework Statement Hi, I have a quick question about an experiment I am doing. I did an experiment where I rolled a ball over a flat surface and dropped a ball from a height, and I was asked if the ball rolling over the flat surface (1-d) motion is subject to constant velocity? I was also...
  44. M

    MHB Calculate Equilibrium Constant of 2BrCl <=> Br2 + Cl2

    bromine monochloride dissociated on heating the following equation 2BrCl <=> Br2 + Cl2 .9 moles of BrCl were heated in a 5 liter vessel until equilibrium was established . the amount of free chlorine in the mixture was found to be .4 moles calculate the equilibrium constant for the reaction...
  45. mertcan

    Maxwell’s equations with varying charge but constant current

    Hi, initially I would like to share this link related to derivation of maxwell equation : http://www.physicspages.com/tag/amperes-law/ My question is : in this link, it states interesting situation in electrodynamics is one where the current density is constant in time, but the charge density...
  46. G

    A hot air balloon rises at a constant acceleration

    Homework Statement A hot air balloon is released from the ground & rises up with a constant acceleration of 4 m/s^2. When it is 16 meters above a sandbag is dropped. What is the time taken for the sandbag to hit the ground? Homework Equations v^2=u^2+2as v=u+atThe Attempt at a Solution...
  47. H

    Integral constant for internal energy of an ionic liquid

    Integral constant for internal energy of ionic liquid I have a question, and I will be really grateful if someone helps me. I have a polynomial equation for internal energy which I calculated by integration an equation of state formula, which is based on density. But, because I calculated this...
  48. H

    Integral constant for internal energy of ionic liquid

    Integral constant for internal energy of ionic liquid I have a question, and I will be really grateful if someone helps me. I have a polynomial equation for internal energy which I calculated by integration an equation of state formula, which is based on density. But, because I calculated this...
  49. M

    Charge moving with a constant linear velocity....

    Charge moving in constant linear velocity does not produce magnetic field... If not, please provide an explanation...
  50. M

    Whether constant acceleration and zero acceleration are the same

    In the equation v=u+at, u=5 m/sec and a=0, then v=5 m/sec. That means the body is moving with a constant velocity of 5 m/sec. In a velocity-time graph, the equation produces a straight horizontal line. Some texts say the body is moving with zero acceleration and others say it is moving with...
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