quantities Definition and 191 Threads

Hi, I have a little doubt. I have, referred to the Sun, the cartesian positions and velocities of an asteroid (in x, y and z coordinates - 6 values). I can easely calculate the polar coordinates (longitude and latitude - along with distance). My doubt is: how do I calculate the longitude and...

my question is why physical quantities need a unit?

Homework Statement If 15 workers can pave 18 driveways in 24 days, how many days would it take 40 workers to pave 22 driveways Homework Equations Actually i don't know which equation should be used for 3 quantities. I know the eq for two quantities. Because we increasing labours so we would...

I've been asked by someone with minimal background in physics to explain what vector and scalar quantities are and give examples. Here are my thoughts: A scalar is a quantity that has a magnitude only, it is completely specified by a single number. Importantly, it has no directional dependence...

[Mentor's note: This question was split off from: https://www.physicsforums.com/threads/meaning-of-physical-quantities-and-division.880214/] What does this differential "d" mean? Why say dE instead of E? or

I read this interesting thread trying to find an answer to my questions (and I got even more confused). I study radiometry units in context of computer graphics. I have a few questions, starting from the basic ones: 1. Following AlexS's note, why is speed=distance/time and not distance*time? 2...

Homework Statement See attached photo Homework Equations Kirchhoff's current law[/B] The Attempt at a Solution So, I was solving for I3 and got the correct answer, but I want to be sure that I arrived at the right answer by using a reliable thought process. I don't want to get lucky! So...

I have done the example for momentum. And I gather that scalar*vector=vector. I know that mass and KE is scalar, velocity is vector. Can someone show me proofs like for what I have said above. Not just mass is scalar because it does not have direction etc. Thank you.

'Flux' is often used to describe quantities associated with a surface integral. I wonder if there are corresponding terms for the line and volume integrals. Linflux? Volux?

If a metric admits a Killing vector field ##V ## it is possible to define conserved quantities: ## V^{\mu} u_{\mu}=const## where ## u^{\mu}## is the 4 velocity of a particle. For example, Schwarzschild metric admits a timelike Killing vector field. This means that the quantity ##g_{\mu 0}...

Consider this self-evident proposition: "If object A has the same mass as object B and object C separately, then object B has the same mass as object C." Why isn't this stated as a law, but the zeroth law of thermodynamics is? Is there a physical quantity u such that the u of A is equal to the...

Hello! (Wave) I am looking at the general form of the Simplex algorithm with the use of tableaux. $\overline{x_0}$ is a basic non degenarate feasible solution and thus the columns $P_1, \dots, P_m$ are linearly independent. The first step is to create a $(m+1) \times (n+4)$ matrix as follows...

Hello Forum, I have a couple of kinematics questions. The position of a point object is given by the position vector x(t). Speed is v(t)=dx(t)/dt and the acceleration a(t)= dv(t)/dt. What if we wanted to know the velocity and/or the acceleration as a function of position, i.e v(x) or a(x)...

In quantum mechanics, a physical quantity is expressed as an operator G, then the unitary transformation coresponding to the physical quantity is expressed as exp(-iG/ħt), being also an operator, where t is the tranformation parameter. G is actually the conservative quantity corresponding to the...

Homework Statement A 2.5 MeV photon is moving in positive x-direction and an electron in the opposite direction at a velocity of 0.99c. Calculate their common total energy, momentum and total rest mass.Homework Equations Relativistic EquationsThe Attempt at a Solution I have some concerns...

Hello ppl ! If i find that a physical quantity (lets say angular momentum operator vector L) is conservative (this means [H,L]=0 - H=hamiltonian ) then its 3 components Lx , Ly and Lz are being conserved too ? That happens with every conservative vector operator ? Like spin vector S and his...

so for surface integral for scalar quantities. Why do we use cross product not dot product in the integral? but can we just add an unit normal vector n to make the direction the same? My question seems really stupid too a lot people, but this is really my confusion to surface integral. please...

I've been asked to find the conserved quantities of the following potentials: i) U(r) = U(x^2), ii) U(r) = U(x^2 + y^2) and iii) U(r) = U(x^2 + y^2 + z^2). For the first one, there is no time dependence or dependence on the y or z coordinate therefore energy is conserved and linear momentum in...

A problem on an assignment I'm doing deals with a cart of mass m1 which can slide frictionlessly along the x-axis. Suspended from the cart by a string of length l is a mass m2, which is constrained to move in the x-y plane. The angle between the pendulum and vertical is notated as phi. The...

Homework Statement A wheel of radius R starts from rest and accelerates with a constant angular acceleration α about a fixed axis. At what time t will the centripetal and tangential acceleration of a point on the rim have the same magnitude? Homework Equations acp=r x ω2 at= r x α ω= 2π / T...

I want to ask the graph of gravitational force against r and gravitational potential energy against r. First, about gravitational force against r The shape of the graph is straight line from origin until the surface of the sphere and then curve (decreasing). I understand about the decreasing...

Hello everyone, I'd like to know if my understanding of local and integral quantities is clear. An integral quantity refers to the entire physical system, it is not defined point by point. A local one is defined point by point, for example ρ(x,y,z). Can I consider the charge dq as a local...

Hello there, I have a confusion between dimensions and units! All of others tell me its not unit but some use units! Please verify the following Quantity Dimension Length L Mass M Time T Temperature Θ Amount of...

If I have an arbitrary quantum many-body model, what is the method to calculate the the conserved quantities if the model is integrable. If it is hard to explain, can you recommend some relevant books for me? Thanks a lot!

Given a basic Lagrangian, how would I determine invariant quantities? My hunch says it would be quantities that do not depend on position or time? Saying that, perhaps using the Lagrange equation to solve for equations of motion and along the way whatever terms disappear would be my invariant...

Hi all, I am preparing for my "second chance exam" in analytical mechanics. It is a graduate course i.e. based on geometry. (Our course notes are roughly based on Arnold's book). I was able to find some old exam questions and one of those has me stumped, completely. The question gives 3...

I am trying to understand why I can specify the specific volume v of a fluid element as a function of the equilibrium pressure, p, and the equilibrium entropy, s. This is for example done in this article http://www.sno.phy.queensu.ca/sno/str/SNO-STR-95-051.pdf , on this website...

This bothers me, and the question is simple: If am working with a non-minkowski metric g, when raising or lowering indexes of electromagnetism quantities, for example the electromagnetic tensor F, or the vector potential A, should I use my curved spacetime metric g or the minkowski metric n?

We know that for constant pressure thermodynamic processes, dH=dqp. My question is, does it implies that only reversible work is possible in this processes so that dw=0 because dv is zero? In addition, does qv necessarily be reversible heat transfer in this case? What if the heat transfer is...

Why are some quantities vectors while others aren't? For example, we can calculate both current and current density, but why do we only consider current density to be a vector and current a scalar quantity? Is it a purely arbitrary convention or is it something more mathematically fundamental? I...

Homework Statement A particle moves along a trajectory with constant magnitude of the velocity |\stackrel{→}{v}|=\stackrel{→}{v0} and constant angular momentum L⃗ = L⃗0. Determine the possible trajectories. Homework Equations d(L⃗)/(dt)=\stackrel{→}{N} where \stackrel{→}{N}=torque...

You probably know that for two commutative quantities x and y,we have: (x+y)^n=\sum_{r=0}^n \left( \begin{array}{c} n \\ r \end{array} \right) x^{n-r} y^r Now I want to know is there a similar formula for the case when x and y don't commute and we have [x,y]=c and [x,c]=[y,c]=0 ? Thanks

Homework Statement All the following are units of basic quantities except ______. Select one: a. second b. slug c. kilogram d. meter e. pound Homework Equations The Attempt at a Solution i have eliminated the answers a, c,d i now the answer is between pound and a slug on...

1. a.if john finished the job in 8 days, what was the part he finished in n days? b. by how much 4k greater than 4h? c. represent the amount of salt in x gallons of a 25% by volume of salt in solution water. d. represent 3 consecutive integers if the smallest is n. answers a. n/8 b. 4h+4k c. i...

Homework Statement d1 = 2.53 cm +/- .05 cm d2 = 1.753 m +/- .001 m 0 = 23.5 degrees +/- .5 degrees v1 = 1.55 m/s +/- .15 m/s Using the measured quantities above, calculate the following. Express the uncertainty calculated value. Homework Equations d3 = 4 ( d1 + d2) The...

d1 = 2.53 cm +/- .05 cm d2 = 1.753 m +/- .001 m 0 = 23.5 degrees +/- .5 degrees v1 = 1.55 m/s +/- .15 m/s Using the measured quantities above, calculate the following. Express the uncertainty calculated value. a = 4 v1^2 / d2 a = 4 (1.55 m/s +/-.15 m/s)^2 / 1.753 m +/- .001 m a = 6.8 m/s...

Homework Statement A two-level system is spanned by the orthonormal basis states |a_{1}> and |a_{2}> . The operators representing two particular observable quantities A and B are: \hat{A} = α(|a_{1}> <a_{1}| - |a_{2}> <a_{2}|) and \hat{B} = β(|a_{1}> <a_{2}| + |a_{2}> <a_{1}|) a) The state...

When tiny droplets of hot water touch your hand you don't feel much pain but when large amount of hot water spills on your hand it will cause serious injuries. Why? - is this due to the heat energy in the tiny droplets of water is lesser so the energy transferred to the hand is lesser...

Homework Statement Calculate the number of moles and mass of BaCl2 and NaCl in the original mixture. Homework Equations We prepared a solution of 0.35M Na2SO4. We then obtained an unknown mixture of BaCl2•2H2O and NaCl, weighed 1 g and added it to 200 mL of water and 10 mL HCl. Finally we...

Suppose we have a Lagrangian \mathcal{L(\phi, \partial_\mu \phi)} over a field \phi, and some variation on the field \delta \phi. If this variation induces a variation \delta \mathcal{L} = \partial_\mu F^\mu for some function F^\mu, then Noether's Theorem tells us that if we construct the...

Alan Turing made the following claim: "It is easy to show using standard theory that if a system starts in an eigenstate of some observable, and measurements are made of that observable N times a second, then, even if the state is not a stationary one, the probability that the system will be...

Homework Statement A one-dimension system is in a state described by the normalisable wave function Ψ(x,t) i.e. Ψ → 0 for x → ±∞. (a) Show that the expectation value of the position ⟨x⟩ is a real quantity. [1] (b) Show that the expectation value of the momentum in the x-direction ⟨p⟩...

hi, please explain can by using suitable operator we can find any physical quantity- as by using hamiltonian on wave function we can find energies by the eigenvalues? thanks wasi-uz-zaman

Hi guys, The title pretty much says it. Say you have a very simple 3D Lagrangian: L = \frac{1}{2}m(\dot{x}^2 + \dot{y}^2 + \dot{z}^2) - V So How do you tell what is conserved from a generic potential? I know for example that if V = V(x,y,z) then the total linear momentum is not...

The title pretty much says it all, but let me elaborate on the source of confusion. VIM defines quantity as: Other definitions I found are extremely circular. They typically go like this, "a physical quantity is a property that can be quantified". In other words, they explain quantity with...

http://img842.imageshack.us/img842/7200/img0103iu.jpg Mainly concerned with the first half of the page. You'll see that it derives for a system in contact with a constant-temperature, constant-pressure heat bath that the change in Gibbs entropy is always less than or equal to zero. Equality...

What are the difference between extensive and intensive quantities?

Hi, I am not a chemist but maybe there is somebody who can help me. I need a put together an emergency plan as part of a college law assignment on European Seveso directives. My case study has 17t of Hydrogen and 8t of Fluorine. Both of which combine satisfy the requirement for a lower...

Hello, Of the different rotational quantities of motion--angular velocity, angular acceleration, torque, angular momentum, etc.--, which of them has their direction perpendicular to the plane of rotation (not sure if I worded that correctly)? I am pretty certain that torque has its...

Need help differentiating multiple quantities Homework Statement f′(x) = (x − 1)(x − 2)^2(x − 3)^3(x − 4)^4(x − 5)^5 I need help in trying to differentiate this equation. I know could use a combination of the chain and product rule to figure it out, but my teacher said that doing so would...