What is Point: Definition and 1000 Discussions

The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at a standard pressure such as 1 atmosphere or 100 kPa.
When considered as the temperature of the reverse change from liquid to solid, it is referred to as the freezing point or crystallization point. Because of the ability of substances to supercool, the freezing point can easily appear to be below its actual value. When the "characteristic freezing point" of a substance is determined, in fact the actual methodology is almost always "the principle of observing the disappearance rather than the formation of ice, that is, the melting point."

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  1. R

    What's the point of having a dress code stricter than business casual?

    Nowadays a lot of people like to fashion themselves in a way that is less traditional. You might see men wear make up or men and women coloring their hair some color that isn't naturally possible. Since society is so free, even among serious scholars (as I see in my department), what is the...
  2. D

    How to calculate the electric field at a point on the axis of two rings

    Hi! I need help with this problem. I tried to solve it like this: First I calculated the electric field of each ring: Thus the electric field at a point that is at a distance z from the ring is ##E=\frac{Qz}{4\pi\epsilon_0(z^2+r^2)^{3/2}}##, Thuss for the upper ring, the electric field would be...
  3. F

    I The Equivalence Principle as a Starting point of GR

    Hello World, I have understood the following: in SR, time intervals and space intervals (distances, lengths) are relative and inertial reference frame dependent. Space and time is not absolute anymore. However, acceleration is still absolute: different inertial frames see the same acceleration...
  4. Z

    Conductor that has the highest melting point

    Hoping for feedback regarding engineered conductors that has high melting points (>4000C). Does anyone perhaps know of such metallic alloys or conductive material? (please, no 2D/1D materials -- exotic materials/alloys are OK, just has to be able to be made in bulk!) Thank you!
  5. D

    I Defining a Point on a Manifold: Intrinsic vs Embedded Space

    Say you have some n dimensional manifold embedded in a higher space. what is the best way to describe or define a point on a manifold with or without coordinates. How could I do this either intrinsically or using the embedded space. Would you use the tangent space somehow using basis vectors?
  6. Q

    Wicks Contraction without contractions at the same spacetime point

    If I'm computing $$\mathcal{T} \langle 0 | \prod_i^Ne^{\imath \beta_i \phi(x_i)} | 0\rangle $$ where the contractions at the same spacetime point are ignored, can I simply insert a complete set of states (product now outside of expression) between each exponential to give $$\mathcal{T}...
  7. Wrichik Basu

    MATLAB Forcing the best fit line to pass through a certain point (Octave)

    I have the following code in Octave: h = [29.3 25.3 19.7 16.0 10.9]; v = [0.53 0.47 0.37 0.29 0.21]; plot(h,v,'obk') hold on p = polyfit(h,v,1); y = polyval(p,h); plot(h,y,'-bk') And I get a good graph: I can extrapolate the best fit line using the following code: x = -1:0.01:11; >> y =...
  8. QuarkDecay

    A Equilibrium point of matter and radiation density

    We want to calculate the ao/a(teq) of the equilibrium point between ρm and ρr (ρm= ρr ) My book solves it this way; ρm(t) / ρr(t)= a(t) ⇒ ⇒ (ρm/ ρr)teq =1 = = (ρm/ ρr)o * a(teq)/ ao I don't understand the a(teq)/ ao part. If ρm(t)= ρο/αo3 and ρr(t)= ρο/αo4 then it should be ρm(t)/ ρr(t) =...
  9. Arman777

    I Fınding the position of a point on the line

    Let us suppose we have a line ##l_1 = ax + by + c = 0## and we have a point P, ##P(x_p, y_p)## that is outside of this line. If we draw a perpendicular line from point ##P## to a point on the ##l_1##. What would be the coordinates of this point ? I know there are many ways to do it. But I am...
  10. K

    Heating up plastic before its melting point -- could it be bad?

    I am interested in a water heater found in consumer market, however, it's made of kind of plastic, I often "feel" that there must be some problem heating up something like plastic. I understand that it should be tested and safe before putting into the market, however, I still wish to know -...
  11. B

    Stationary Point - Possible Values

    Please refer to the image attached
  12. F

    Application point of the lift force and pitching moment

    Hello As the angle of attack of an airfoil changes, the lift force ##L## changes both in magnitude and position (not in direction, always upward). The force location is a point called the center of pressure ##x_{cp}##. It is possible to transfer the force to any another different point along...
  13. J

    I Trying to get the point of some Group Theory Lemmas

    There are two related Lemmas in Schaum's Outline of Group Theory, Chapter 4 that seem excessively convoluted. Either I am missing something or they can be made much simpler and clearer. Lemma 4.2: If H is a subgroup of G and {\rm{X}} \subseteq {\rm{H}} then {\rm{H}} \supseteq \left\{...
  14. P

    How to calculate the failure point of a pin

    Hi, I have a device I'm suspending from a chain and the chain attaches to the body with a pin. I'm curious how you would calculate how much weight a pin like that could take before failing. There is a block on the body and a bar on the end of the chain that slots into the block and the pin goes...
  15. L

    Absolute equation to find the max and min point

    X-1 > 0 x>1 $x^2$ - 2x >0 X>2 For 0<x<1 f(x) = -x +1 + -$x^2 $ +2x For 1<x<2 f(x) = x -1 - $x^2 $ + 2x Find each of the equation the critical point By using f'(x) = 0 And decide which is max and min I get x = 1/2 and x = 3/2 But it's wrong Why?
  16. bhanum

    B The Cat's Perspective: Can Macroscopic Bodies Be in Superposition?

    Hi, In the Schrodinger's Cat thought experiment, we say that the cat is in a superposition of states of being either dead or alive. But isn't that opinion biased from being outside of the system? From the cat's point of view, it is either dead or alive but never both. The same argument can be...
  17. RichardWattUK

    I "Map" point between coordinate systems

    I've taken on a new job recently where I'm having to maintain an existing application that generates a points profile to drive a CNC machine and part of it projects points from an axial plane (which represents the machine's working axis) onto another plane which (I think) acts as as a...
  18. J

    I How can an asteroid get caught at a Lagrange point without a "brake"?

    Talking about the Jupiter Lagrange points at 60 degrees only. Hard to imagine a scenario where an asteroid comes from outside or inside the orbit of Jupiter and stops at a Lagrange point. That's like tossing a cone on a table and trying to make it end up standing on its nose. Or make the nose...
  19. Arman777

    Python equation solver, I'm getting a floating point error

    I am trying to solve the equation like this, from sympy.solvers import solve from sympy import Symbol import math x = Symbol('x') A, B, C, D = 0.59912051, 0.64030348, 263.33721367, 387.92069617 print(solve((A * x) + (B * math.sqrt(x**3)) - (C * math.exp(-x / 50)) - D, x , numerical = True))...
  20. N

    How to transmit a signal (530 - 550 Khz) to a point

    Hi everyone, I'm pretty new to electromagnetism and have no experiences in this topic. I have a signal generator (Digital Dual Channel Funktion Signal Generator) and want to generate two signals (530 and 550 Khz signal) and want to transmit these generated signals to the points on a table...
  21. Rahulx084

    Questions about the Point Function (Thermodynamics)

    We know from first law of thermodynamics for a closed system that ##dE##=##\delta Q## -##\delta W## , my question is that for a closed adiabatic system net heat transfer =0 this mean net change in energy = work done , does that mean for an adiabatic system work done is a point function as...
  22. nomadreid

    I Kripke's fixed point for truth predicate: justification?

    If I understand correctly (dubious), given a consistent theory C (collection of sentences), Kripke proposes to add a predicate T so that, if K = the collection of all sentences T("S") for every sentence S in C, ("." being some appropriate coding) then the closure of K∪C forms a new theory C*...
  23. sergiokapone

    I Derivation of Geodesics Eq from EM Tensor of Point Particle

    The energy-momentum tensor of a free particle with mass ##m## moving along its worldline ##x^\mu (\tau )## is \begin{equation} T^{\mu\nu}(y^\sigma)=m\int d \tau \frac{\delta^{(4) }(y^\sigma-x^\sigma(\tau ))}{\sqrt{-g}}\frac{dx^\mu}{d\tau}\frac{dx^\nu}{d\tau}.\tag{2} \end{equation} The covariant...
  24. F

    A Why do we know that an elementary particle is a point particle?

    Elementary particle can be consider as a "wave packet" of the field,but a "packet" of field must have a size.Why do we know elementary particle is point particle?
  25. migueldbg

    Potential from point charge at distance ##l## from conducting sphere

    After looking around a bit, I found that, considering the polar axis to be along the direction of the point charge as suggested by the exercise, the following Legendre polynomial expansion is true: $$\begin{equation}\frac{1}{|\mathbf{r} - \mathbf{r'}|} = \sum_{n=0}^\infty...
  26. J

    Adding xylitol to hot water lowers the boiling point and makes it boil

    This probably occurs with salt too but let's concentrate on xylitol: you heat water till it boils, put the hot water in a cup and add a tsp of xylitol. It boils again violently for a couple of seconds. The high school explanation is that the boiling point of the water is lowered. I'd like to...
  27. A

    An electron is placed at Point P, Calculate the Potential Energy

    Not quite sure how to approach this question - do I need to calculate -qEd for all three charges and then the electron and add them together? Thanks
  28. T

    Why is the torque about R used in this problem?

    So I let x be the distance from P. I then considered moments about R and got this: 1) (40g)(x-3) = 40gx - 120g and this is anticlockwise 2) (30g)(0.5) = 15g and this is anticlockwise 3) (2.5g)(2) = 5g and this is clockwise And then by equating clockwise and anticlockwise I get this: 40gx -...
  29. R

    Calculating the half maximum point of a function

    This is the form of the function above: I started by equating (1) to 1/2: $$T(\varphi)=\frac{r^{2}+\tau^{2}-2\tau\cos\varphi}{1+\tau^{2}r^{2}-2\tau r\cos\varphi} = \frac{1}{2},$$ which can be rearranged to: $$2r^{2}+2\tau^{2}-1-\tau^{2}r^{2}=2\tau\left[2-r\right]\cos\varphi$$ using...
  30. B

    Potential at a point multiple choice question ( aqa)

    I understand how they arrived at the answer of 2Q , but i have a couple of questions on this. If one of the charges were negative for example how would the resultant potential be found then? at the middle point would i add the positive charges and subtracted the negative ? Also what would the...
  31. R

    A dielectric plate and a point charge: the problem with series

    The problem of the interaction of a point charge with a dielectric plate of finite thickness implies the existence of an infinite series of image charges (see http://www.lorentzcenter.nl/lc/web/2011/466/problems/2/Sometani00.pdf). I introduce notations identical to those used in this work. The...
  32. W

    I Why is F=dU/dx=0 either side of inflexion point?

    In Tipler & Mosca 5th edition p173 it defines neutral equilibrium as a point in a U-x curve where ##\frac{dU}{dx}=0## and also ##\frac{dU}{dx}=0## for a small displacement either side of the point. However I do not understand why ##\frac{dU}{dx}## remains ##0## either side of the inflexion...
  33. Kasiopea

    Why is the x-component of the electric field at point P positive?

    I got the answer: E(P)=(k*Q)/(3î )−(k*Q*ĵ) /2 Can someone confirm if this is the right answer?
  34. B

    A Point source with Dirichlet Boundary

    hi, all great brains, I have a question about BVP, which confused me a while, maybe someone can help to clarify it. For a point source with Dirichlet boundary in a 2D domain, the response at any coordinate except the source point is dependent on the surface of the source, for example, heat...
  35. S

    Potential at the origin due to an infinite set of point charges

    Summary: Potential at origin of an infinite set of point charges with charge (4^n)q and distance (3^n)a along x-axis where n starts at 1. From V=q/r, we find Vtotal=sum from 1 to infinity of (4/3)^n(q/a), which diverges. There cannot be infinite potential because there is a finite electric...
  36. J

    Shortest path to a point that doesn't pass through the given circle

    This is my attempt at a solution. Point A is the center of the circle (6,8) and Point B is the given point (12,16). I believe that the shortest path would be the one that is equal to the sum of CE and EB or its symmetrical complement. (I forgot to put a point where the top line intersects the...
  37. emarie

    Calculate the magnitude of the velocity at point from a given equation, a(t)

    These questions keep appearing in my past-papers and yet at no point in the course notes can I find a worked solution. Unfortunately I'm not sure where to start. My initial thoughts were regarding getting an equation using known values but w.r.t. to t and integrating for v, but like I said I...
  38. H

    How far will the middle point of the beam sag under load?

    I tried to use F/S = E.ε to find the new length after deformation and than use pytagoras theorem in right angled triangle to find how much did the middle point lower. But it was said to me that my method is wrong and that there exists some formula to solve it. Can you please tell me where could...
  39. A131313

    Why is the Kinetic Energy 0 at an infinite distance away from a point?

    Hello! I'm trying to understand the concept of escape velocity, and I know you equate the initial mechanical energy to the final mechanical energy, where the final mechanical energy is at a distance of infinity. I know that the gravitational potential energy approaches 0 as the distance r gets...
  40. lekh2003

    Why does salt reduce the freezing point of water?

    I've been looking into how adding sodium chloride or calcium chloride to snow reduces the freezing point, and why this occurs. The really simple reason I found on this website: https://www.thoughtco.com/how-salt-melts-ice-3976057 , which simply stated that the salt ions get in the way of the...
  41. Alif Yasa

    Finding the speed of the cylinder's point of mass

    I already got the answer for the case a but at the case b, i don't know how to sum all of the torques. I'm thinking of using integral, but i don't know where to put the pivot point for the torque. I don't know how to search for the pivot point. Can anybody give me hints so i could find the pivot...
  42. M

    I Why do we ignore the contribution to a surface integral from the point r=0?

    Let ##V'## be the volume of dipole distribution and ##S'## be the boundary. The potential of a dipole distribution at a point ##P## is: ##\displaystyle\psi=-k \int_{V'} \dfrac{\vec{\nabla'}.\vec{M'}}{r}dV' +k \oint_{S'}\dfrac{\vec{M'}.\hat{n}}{r}dS'## If ##P\in V'## and ##P\in S'##, the...
  43. P

    MHB Time for truck to go down ramp and reach point B

    A 2000 kg truck is resting at the top of a parking lot ramp which is at a 15 degree slope. It is then shifted into Neutral and starts moving. How long does it take the truck to get from A to B in seconds? There is a 15 degree slope on the ramp. uk is 0.08 Assume there is no air resistance.
  44. M

    I Why ignoring the contribution from point r=0 in eq (1) and (2)?

    The potential of a dipole distribution at a point ##P## is: ##\psi=-k \int_{V'} \dfrac{\vec{\nabla'}.\vec{M'}}{r}dV' +k \oint_{S'}\dfrac{\vec{M'}.\hat{n}}{r}dS'## If ##P\in V'##, the integrand is discontinuous (infinite) at the point ##r=0##. So we need to use improper integrals by removing...
  45. S

    A What is the relationship between focal length and focus point in convex lenses?

    First of all, Let me present some of the things I found from research. (considering convex lens) Interpretation 1 => Focal length is the distance from the center of the lens to the point where all rays converge. Interpretation2 => Focal length is the distance from the point of convergence to...
  46. A

    Moment of a Force About a Point

    Homework Statement I'm a bit confused on when a force creates a moment about a point, and when it does not. In particular, in the attached diagram, would F be able to produce a moment about point A? I initially thought that wouldn't be possible as A lies on the same line as F, but since F does...
  47. P

    Voltage measurement of a point charge

    If we have a point charge of significant value, would osciloscope measure voltage if we just point the electrodes in two diffrent point in space?
  48. N

    Finding the Parameters for the Curve y=asin(x-b)+c

    <Moderator's note: Member has been informed to separate different question into different threads in the future.> 1. Homework Statement Please see picture attached... The diagram shows the curve with equation y = f (x) The coordinates of the minimum point of the curve are (–2, –1) (a) Write...
  49. L

    I Finding the coordinates of a point on a sphere

    I have three points: A, B and C, which are all on the surface of the same sphere. I need to find the xyz coordinates of C. What I know: - the radius of the sphere - the origin of the sphere - the xyz coordinates of A and B - the arc distance from A to C and from B to C - the angle between AB and...
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