quantities Definition and 191 Threads

Because of ##\sqrt{2}## be a irational numbers I think it is impossible and there is no scales that can measure irational quantity. May be approximately. But 2 kg can be measurable. İt is my efforts and thougts.

Is there a neat way to "not" run the internal Boltzmann solver (for perturbations) in CLASS code and rather just solve for the background quantities? This way I can save the time otherwise spent in evaluating the perturbations and transfer functions. I am only interested in the time evolution of...

Hi everyone! It's about the following task. Partial molar quantities a) How are partial molar quantities defined in general? b) If X is an extensive state variable and X̅ is the associated partial variable, what types of variables must X̅ have? c) Is the chemical potential of component i in a...

I'm confused with the term "rated". I checked this webpage though I am not confident about it's reliability. Context: Motor ratings etc. Does it mean maximum? Maximum in what regard? Heat produced/temperature? Is there a more reliable source on how manufacturers determine the 'rated'...

Hi, Results from the previous task, which we may use I am unfortunately stuck with the following task Hi, I have first started to rewrite the Hamiltonian and the angular momentum from vector notation to scalar notation: $$H=\frac{1}{2m}\vec{p_1}^2+\frac{1}{2m}\vec{p_2}^2-\alpha|\vec{q_1}-...

Hi every one.How can i prove the below equation? And then that it's Lorentz invariant quantitude ? Thanks for your help

Let's say I have ##F=mg \tan \alpha## and want to calculate ##F##. I know ##m=(1.0 \pm 0.5)\,\mathrm{kg}## and ##\alpha=(20.5 \pm 0.5)° ##. How to calculate ##F=( 3.7 \pm ?)\,\mathrm N##? What is the general method of determining a measurement error in these cases?

I am on a journey to not just understand how to manipulate physics equations but to understand why they work , and how they describe physical phenomena. I understand how division combines physical quantities. I have this much physical quantity 'per' this much physical quantity. It puts 2...

Answer: Did I draw them right?

I'm looking for a reference text for astronomy and astrophysics that provides astrophysical and cosmological data since Cox's 1999 update to CW Allen's Astrophysical Quantities. Among other reasons, I'm hoping for statistical data on confirmed exoplanets, which did not exist in 1999.

We think of length and time as the first fundamental quantities and velocity as the first derived quantity but any two determine the third so we would be completely justified in defining velocity as a fundamental quantity and one of length or time as the other, with the remaining being the first...

a) I managed to obtain some results that are roughly around what is given in the answers. Because \varepsilon_{st} and \varepsilon_{\infty} are values of \varepsilon_{1}, I used this approximation: n\approx \frac{1}{\sqrt{2}} (\varepsilon_{1}+\sqrt{\varepsilon_{1}^2})^{1/2} -> \varepsilon_{1} =...

Hi If x(t) is considered to be small so that higher powers ( greater than 2 ) can be neglected in a calculation does that also imply that the time derivative of x(t) can be considered small and powers greater than 2 be neglected ? Thanks

For example, can you predict the permittivity and permeability of a substance if you know what the atomic composition is? Is it a stat mech problem?

Hi, please correct me if I use a wrong jargon. If I have discrete symmetries (like for example in a crystal lattice) can I find some conserved quantity ? For example crystal momentum is conserved up to a multiple of the reciprocal lattice constant and it is linked (I think) to the periodicity...

Hello, I am a Brazilian Physics student and would like to ask a question. Why are not all physical quantities related to each other by the degree of precision in the Heisenberg Uncertainty Principle? For example, why is it possible to determine the energy and position of a particle without its...

Hello, In non-relativistic physics (where things move slower than the speed of light), the following physical quantities are invariant and variant (or relative) i.e. vary in value depending on the chosen frame of reference: Variant quantities: time ##t##, velocity ##v##, momentum ##p##...

A quantity ##p## can be expressed as the product of a dimensionless number, ##\lambda_p##, and a unit, ##u_X##:$$p = \lambda_p u_X$$When we write the equation of a physical law, do the symbols represent the physical quantities ##p## or their dimensionless coefficients ##\lambda_p##? That is to...

Let me define the letters before because they will be confusing: ##x##: 3-vector ##v##: 3-velocity ##a##: 3-acceleration ##X##: 4-vector ##U##: 4-velocity ##A##: 4-acceleration ##\alpha##: proper acceleration ##u##: proper velocity One can define the proper time as, $$d\tau = \sqrt{1 -...

I assume this is true because using a passive coordinate transformation of the coordinate system should not effect how we measure something. I don't know if this is enough, hence if my original statement is just trivial, or if there is some deeper underlying thing lurking. Is the statement true...

Summary:: Hi, I am trying to solve the following: A person shovels driveways to earn money. She can shovel 12 driveways in 6 hours. She earns 18$ for each driveway.The person needs 360$ to buy a computer. How may hours does the person need to work? I am using unity method : 18$----6 hour 1...

Hi, I have a question and I was hoping for some help. The reasoning goes something like this: There appears to be two fundamental types of coordinates x - space t - time and there appears to be three types of fundamental transformations - translations - rotations -...

I'm only really just learning how natural units work so forgive me if this seems like a silly question. I was just wondering if someone could verify whether the following line of reasoning is valid (I will use joules instead of electron volts just so we can ignore the e conversion factor for...

In physics, a symmetry of the physical system is always associated with some conserved quantity. That physical laws are invariant under the observer’s displacement in position leads to conservation of momentum. Invariance under rotation leads to conservation of angular momentum, and under...

Please take a look at my first thought experiment: You have 2 coins to place on the table. The distance between them may be between 0 (inclusive) and 1 meter (exclusive). So if you want to store the number 15 you simply set the distance to 0,15m. You can later read the information by measuring...

Wald and Zoupas discussed the general definition of ``conserved quantities" in a diffeomorphism invariant theory in this work. In Section IV, they gave one expression (33) in the linked article. I cannot really understand the logic of this expression. Would you please help me with this?

I already know the fact that angles are physical quantities, but sin, cos of some angles are quantities? Quantities are those things, which can be quantified, are sin, cos, tan be quantified through measurement, if yes then other mathematical functions should also be categorised as physical...

here's the question: a = b/e b = 1 kg m-1 e = 1 kg m-2 what is a? including units I assume it's to do with cancelling out the units when you divide but I really don't know what the answer is

My question is about some physical quantities which two observers in two respective inertial frames will find the same. I wonder are there any such quantities? Some books say force, speed of light etc are constants for both the observers. Please guide me on this. Regards.

In SR, we know that ##\vec E \cdot \vec B## and ##E^{2}-B^{2}## are invariant. Although I can prove those two invariant physical quantities mathematically, I do not know how to find at least one example to demonstrate that ##\vec E \cdot \vec B## and ##E^{2}-B^{2}## are invariant. Many thanks!

Homework Statement Two parallel-plate capacitors with the same plate separation but different capacitance are connected in parallel to a battery. Both capacitors are filled with air. The quantity that is NOT the same for both capacitors when they are fully charged is: A. potential difference...

Homework Statement Homework EquationsThe Attempt at a Solution I don't know how to do the last part. What are the additional conservation laws? I don't think momentum is conserved because there is force acting on the particle. I don't think angular momentum is conserved too because there is a...

Homework Statement Homework EquationsThe Attempt at a Solution How do I calculate part d? I know that (m2-m1)v0 = m2v2+m1v1 where v0 = root (2gh), v1 and v2 are the new velocity of the masses (m2+m1)v02 = m2v22 + m1v12 I also know that v2-v1=2v0 but how do I separate the KE of mass 2?

Homework Statement N point particles of mass mα, α = 1,...,N move in their mutual gravitational field. Write down the Lagrangian for this system. Use Noether’s theorem to derive six constants of motion for the system, none of which is the energy Homework Equations Noethers Theorem: If a...

I would like to know where one may operate with tensor quantities in quantum field theory: Minkowski tensors, spinors, effective lagrangians (for example sigma models or models with four quark interaction), gamma matrices, Grassmann algebra, Lie algebra, fermion determinants and et cetera. I...

Homework Statement Hi Given the linear velocity formula: v* v^ = r*ω(-sinθi^ + cosθj^) i^, j^, v^ - unit vectors I'm to prove that v^ has direction, turn and magnitude Magnitude: |v^| = sqrt((-sinθ)^2 + (cosθ)^2) = 1 (as is also stated in unit vector's definition) Direction and turn...

Hello! I am reading about spherical geometry and for a static system and based on the metric, ##p_0## and ##p_\phi## are constant of motion. I am not sure I understand in which sense are they constant? The energy of a particle measured by an observer depends on the metric (so on its position) in...

Homework Statement Hi, I'm doing the double pendulum problem in free space and I've noticed that I get two different conserved values depending on how I define my angles. Obviously, this should not be the case, so I'm wondering where I've gone wrong. Homework EquationsThe Attempt at a Solution...

Must two quantities have the same dimensions if you are using one quantity as an exponent in raising other to a power? What is the dimension ( or dimensionless) of '2' in mv2/r ?( v is raised to the second power)

Hi Everyone! I have done three years in my undergrad in physics/math and this summer I'm doing a research project in general relativity. I generally use a computer to do my GR computations, but there is a proof that I want to do by hand and I've been having some trouble. I want to show that...

"Ghosts of Departed Quantities" And a host of ones own deity?

Homework Statement Verify that the sum of three quantities x, y, z, whose product is a constant k, is maximum when these three quantities are equal. Homework Equations w = x + y + z k = x * y * z The Attempt at a Solution Assuming that my understanding of the question is correct i.e. that we...

Homework Statement Question attached Homework Equations The Attempt at a Solution part a) ##ds^2=\frac{R^2}{z^2}(-dt^2+dy^2+dx^2+dz^2)## part b) it is clear there is a conserved quantity associated with ##t,y,x## From Euler-Lagrange equations ## \dot{t}=k ## , k a constant ; similar for...

In a lecture on introductory quantum mechanics the teacher said that Heisenberg uncertainty principle is applicable only to canonically conjugate physical quantities. What are these quantities?

I'm stuck on this idea. How are initial radioactive isotope quantities assumed in radiometric dating? There are current abundances for all isotopes, but wouldn't these abundances have been different in the past (much higher)? I honestly can't grasp how radioactive isotopes with short half lives...

Homework Statement Quantities without unit of measure are: A) Necessarily scalar B) Necessarily vector C) Can be scalar or vector D) They are neither scalar nor vector Justify your answer!Homework Equations No equations The Attempt at a Solution For example, the refractive index of a medium...

Homework Statement Consider the Kortweg-de Vires Equation in the form $$\frac{\partial \psi}{\partial t}+\frac{\partial^3 \psi}{\partial x^3}+6\psi\frac{\partial \psi}{\partial x}=0$$ Find the relation between the coefficients ##c## and ##d## , such that the following quantity is conserved...

Several undergraduate and graduate students and I are building a small engine powered by Compressed Natural Gas (CNG). It is a small and straightforward affair, similar to what is found in small equipment such as chainsaws and lawn mowers. I wanted to experiment with Liquefied Natural Gas (LNG)...

I was taught a scalar is a quantity that consists of a number (positive or negative) and it might include a measuring unit, e.g. 6, 5 kg, -900 J, etc. I was wondering if complex numbers like 3 + 7j (where j is the square root of minus 1) can be considered scalar quantities too, or is it that...

In the image above, a centroid with radius 1 is depicted. F1 is pointing directly at point A (which is the center of the circle), and F2 is pointing directly at point B. The radius for finding the torque would be the perpendicular between the center of the object and the force vector, so r1...