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. K

    Rotating rod of negligible mass attached to two point masses

    Homework Statement A uniform rod (length = 2.4 m) of negligible mass has a 1.0-kg point mass attached to one end and a 2.0-kg point mass attached to the other end. The rod is mounted to rotate freely about a horizontal axis that is perpendicular to the rod and that passes through a point 1.0...
  2. M

    A Lorentz-Einstein law of motion for a point particle

    I shall try to expose my question as briefly and clearly as possible. Within a very old and classical approach (Newton), discussions take place in a three-dimensional Euclidean space and the concept of force is represented by a vector which is proportional to the mass of the object at hand (m...
  3. G

    Difficulty with a Point Charge Particle in Electrodynamics

    Point Particle in Relativity and Electrodynamics: “The Classical Theory of Fields” – by Landau and Lifshitz, in its discussion about classical size of a particle, concludes that:- Thus we come to the conclusion that in classical (non-quantum) ‘relativistic mechanics’, we cannot ascribe finite...
  4. J

    I Ordered lattice of topologies on the 3 point set

    So I made this diagram of the order imposed on the set of topologies on a 3 point set. Each small circle is a topology with the circle elements being the open sets. The larger circles join isomorphic topologies together. The ordering was messy when I tried to draw inclusion from each topology to...
  5. Pushoam

    Time for going from one point of earth surface to another

    Homework Statement Homework EquationsThe Attempt at a Solution [/B] The thing to remember is that inside the Earth surface, the gravitational field does not remain inversely proportional to ##r^2##. The equation of motion is ## \ddot r = \frac { -gr} R## ....(1) This means that the...
  6. F

    Schools What's the point of applying to selective grad schools?

    Something's been bothering me about the PhD application process. I know that your future advisor is the most important aspect in choosing a graduate school, and that future success with obtaining postdocs, etc. will depend primarily on your research prowess (which is heavily dependent on if you...
  7. Pushoam

    Flux through an infinite plane due to a point charge

    Homework Statement A point charge q is located a distance d meters from an infinite plane. Determine the electric flux through the plane due to the point charge. [/B] Homework EquationsThe Attempt at a Solution I consider another infinite plane at a distance d in the opposite direction. Now I...
  8. Pushoam

    Flux of a point charge through a circle

    Homework Statement Homework EquationsThe Attempt at a Solution I will try to choose the correct option using the common sense instead of solving it. As d decreases, the flux should increase. For R>>d, only option (a) and (d) satisfy this condition. Now, for choosing between (a) and (d)...
  9. S

    A Is there an alternative form of the zero point energy?

    Hi, is there an alternative form of the zero point energy for free electrons, where there is no space interval L to be quantized in? The zero point energy for electrons in an atom can be simplified to a variant where Z^2 is present in the nominator, however, these are not free electrons. Can a...
  10. wukunlin

    I Putting a point inside a triangle in 3D space

    This may belong to the computing subforum, let me know if this is more true than having it here in the math forum :) My questions are 1) Suppose there is a plane in 3D space and I have 3 points to define it: p1 = {x1, y1, z1} p2 = {x2, y2, z2} p3 = {x3, y3, z3} and I want to put a particular...
  11. nomadreid

    I CMB and the reference point for vacuum energy

    From the basic definition of vacuum energy as being tied in with the Uncertainty principle, I would expect this not to include the Cosmic Background Radiation. Right? On the other hand, in figuring out (a) the Casimir effect, one attributes the force to the field between the plates carrying...
  12. A

    Geometric optics (near point problem)

    Homework Statement A person with a near point of 100 cm , but excellent distant vision, normally wears corrective glasses. But he loses them while traveling. Fortunately, he has his old pair as a spare. If the lenses of the old pair have a power of +2.55 diopters , what is his near point...
  13. A

    I End Point Energy and Q value in beta decay

    I know that Q value of a reaction is the difference between total initial mass-energy and total final mass-energy of all the products. Then shouldn't be this also the maximum kinetic energy and hence endpoint energy of an electron in beta decay. But what I have read endpoint energy ##E_0 = Q +...
  14. Physiker98

    Voltage of thundercloud as point charge

    Hey, Theory: The voltage of a thundercloud is too low to ionize air particles and to produce a thunder. Particles of cosmic radiation are the trigger. I calculated whether the voltage of a thundercloud is enough to ionize air particles but the voltage was always to low. So I wanted to know...
  15. karush

    MHB 12.3.63 Determine the smallest distance between point and a line

    $\text{Determine the smallest distance between point}$ $$P(1,1,1)$$ $\textsf{ and the line $L$ through the origin $L$ has the direction}$ $$\langle -4,-5,8 \rangle$$ ok just barely had time to post this but was ?? about direction presume going off of this $\textit{Distance between point...
  16. B

    Finding regular singular point

    Homework Statement Show that ##x^2y''+sin(x)y'-y = 0## has a regular singular point at ##x=0##, determine the indicial equation and it's roots. Homework Equations For a DE in the form of ##y''+p(x)y'+q(x)y=0##, if both ##p(x)## and ##q(x)## are not analytic at ##x=x_0##, and both...
  17. A

    What is the difference between the yield point and the elastic limit?

    I don't understand the difference between the elastic limit and the yield point. I understand that if you stretch a material within the elastic limit, then the material should return to its normal shape. However, the yield point is described as the point at which a permanent increase in length...
  18. peadar2211

    Determine the stability of a fixed point of oscillations

    Homework Statement I have a system of coupled differential equations representing chemical reactions and given certain initial conditions for the equations I can observe oscillation behaviour when I solved the equations numerically using Euler's Method. However, then it asks to investigate the...
  19. M

    Calculus 3 help -- The equation of a plane and finding a point on that plane

    Homework Statement Why is that we can set two variables zero in an equation of a plane to find a point on that plane? What is the proof for this? Homework EquationsThe Attempt at a Solution
  20. K

    Maths required for rotation point

    Hi The first thing to say about this is that I don’t have a clue where to start. What I’m looking for is somewhere (maybe a website or just a brief introduction) I can study – and learn – about the forces involved and the maths required. _______ Say I have an item/length/beam/weight/etc (C...
  21. Likith D

    Regarding the pressure at a point in a "rested" fluid

    Hey! I just came across this text ; from http://www.feynmanlectures.caltech.edu/II_40.html I tried to find "the law of hydrostatics" on the internet, to find no other mention of it. (would appreciate links to more details on it or any ideas regarding the topic) What is really puzzling is how...
  22. R

    Magnetic field produced at point P

    Homework Statement https://imgur.com/gallery/vCOZq Its question 26, and the figure can be seen at figure 30.26 Derive and expression for the magnetic field produced at point P due to the current carrying wire shown in figure 30.26. The curved parts of the wire are pieces of concentric...
  23. EastWindBreaks

    Why is the height of point 2 same as point 3?

    Homework Statement Homework Equations The Attempt at a Solution Is it an assumption because the difference in height is small?
  24. A

    Effect of a soluble volatile impurity on the boiling point?

    Hi everyone, just wanted to know how does a soluble, volatile impurity affect the boiling point of a liquid? I know it depends on the difference between the boiling points of the liquid and the impurity, but I'm afraid i still didn't get the point. Thanks
  25. J

    Pressure, Volume, and Temperature at a Point in a Thermodynamic Cycle

    Homework Statement Question: https://imgur.com/a/8rUw1 Graph: https://imgur.com/a/Z1oBO Homework Equations Answer for Q1 (Just the formula) : https://imgur.com/a/uesqN The Attempt at a Solution I have realized that from 1-2, there is an increase in pressure, decrease in volume and increase...
  26. I

    Dew Point -- will we be able to see our breath?

    Homework Statement The dew point is the temperature at which moist air becomes saturated with water vapor. We can therefore represent how moist a particular parcel of air is by comparing its actual temperature with its dew point temperature. We see the practical effect of reaching the dew...
  27. C

    Oscillation of a point charge perpendicular to field lines

    Homework Statement Two particles A and B each carry a charge Q and are separated by a fixed distance D. A particle c with charge q and mass m is kept at the midpoint of A and B. If C is displaced perpendicular to AB by a distance x where x<<<D, find the time period of the oscillation of the...
  28. A

    B A programmer's point of view of 2 quantum physics principles

    First, I must say I'm in no way a physicist, I barely understand the basics of quantum physics. And what I will talk about is mostly philosophical anyway. I don't believe myself that "we are in a simulation", it's just food for thoughts. As the title says, it's about 2 quantum things that struck...
  29. PsychonautQQ

    A Fundamental group of n connect tori with one point removed

    Well, for starters, ##\pi(T)##, the fundamental group of the torus, is ##\pi(S^1)x\pi(S^1)=## which is in turn isomorphic to the direct product of two infinite cyclic groups. Before I tackle the case of n connect tori with one point removed, I'm trying to just understand a torus with a point...
  30. L

    Poisson's equation in 1D with point source

    Homework Statement Solve ##\Delta\phi = -q\delta(x)## on ##\mathbb{R}##. Correct answer: ##\phi = -\frac{q}{2}|x| + Ax + B## Homework EquationsThe Attempt at a Solution In one dimension the equation becomes ##\frac{d^2 \phi}{d x^2} = -q\delta(x)##. We integrate from ##-\infty## to ##x## to...
  31. M

    A weightless ladder....but why move the pivot point?

    A weightless ladder 7.0 m long rests against a frictionless wall at an angle of 65° ablove the horizontal. A 72 kg person is 1.2m from the top of the lass. What horizontal force at the bottom of the ladder is required to keep it from slipping? Στ=0 τ=FsinθdSolutions for this question always...
  32. B

    Unique Fixed Point: Prove Contraction Map in Compact Space Has Unique Solution

    Homework Statement Let ##(X,d)## be some metric space, and let ##f : X \to X## be such that ##d(f(x),f(y)) \le a d(x,y)## for every ##x,y \in X## for some ##a \in (0,1)## (such a map is a called a contraction map) If ##f## is a contraction and ##X## is compact, show that ##f## has a unique...
  33. U

    Fluid mechanics - Finding force point of application

    I get how to find vertical and horizontal forces on a submerged surface (vertical = weight of fluid and horizontal = force on vertical projection). I also get how to find the point of application for the horizontal force using a moment balance. But how do you determine the point of application...
  34. karush

    MHB E.12.4 - Find plane through given point and normal to given vector

    $\textsf{write an equation for}$ $\textsf{ The plane through the point (3, 2, -5) and perpendicular to the x-axis}$ 4ok I know this goes thru $3$ on the axis and it is \parallel to the $yz$ plane so is it just $x=3$.
  35. N

    Point me in the right direction -- Quantum Physics learning resources

    I am trying to learn all about Quantum Physics on my own but I am struggling to find credible sources of information. As you are probably aware the internet is filled with misconceptions, crackpot science and weird stuff about spirituality (at least that's what I find when I try and research...
  36. M

    Understanding Point B: Solving for Normal Force at Point B

    I need help understanding point B Point A i get. Normal force at B = m x v2/r - m x g = 1.68 x 12 x 12 /5 - 1.68 x 9.8 = 31.92 N I can't make sense of why the forces are subtracting if A radial and MG are both positive
  37. M

    How to calculate the total energy in the point given.

    Homework Statement The question wants the total energy of point A. Point A is 35 m above the ground and the mass of the objecy is 150 kg. The velocity is 10m/s. (And point B is 20 m above the ground and point c is 26.) Homework Equations Ek= 1/2*mv^(2) Ep=mgh Total= Ek+Ep But for some reasons...
  38. G

    Force exerted on a pivot point of a rigid bar

    Homework Statement A uniform rigid bar of weight W is supported in a horizontal orientation as shown by a rope that makes a 30° angle with the horizontal. The force exerted on the bar at point O, where it is pivoted, is best represented by a vector whose direction is which of the following...
  39. W

    Show that a point lies on the line of striction

    Homework Statement Given M: x(u,v)=β(u)+vδ(u) is a ruled surface with length(β')=1 and length(δ)=1, also supposing δ'≠0. M may be parametrized by y(u,w)=ϒ(u)+wδ(u), where ϒ'⋅δ'=0 (this reparametrization is called the line of striction). Show that any point on M that satisfies xu×xv=0 must lie...
  40. R

    I Two square scale meeting point, when one is moved odd

    There are two square scale. That is, it has marking where there are square i.e marking at 0,1,4,9,16,25 and so on. When one scale is moved, it slide over the other. Now if one scale is moved odd number i.e say 123 , that is, it's zero is placed at 123 over the other scale, now. Now, can one...
  41. J

    Beam Bending of a Linearly Varying Beam with 2 point loads

    I'm trying to design something and rather than solve it using FEA guess and check, I'm trying to mathematically solve it. The part I'm getting stuck at is having 2 point loads on a linearly varying cantilever beam. https://imgur.com/LtHCvCB The closest example I could find to this that was...
  42. X

    How convert a point on an X and Y grid to a angle degree?

    <Moderator's note: Moved from a technical forum and thus no template.> Hello Forum, This post is a spin-off from this post: https://www.physicsforums.com/threads/how-much-would-time-pass-between-watching-the-sun-set.925257/#post-5840279 If I have an X and Y point on a grid that represents...
  43. P

    Calculate strength of the electric field at indicated point

    Homework Statement https://imgur.com/a/wpir4 [/B] a. What is the strength of the electric field at the position indicated by the dot in the figure? Use the following values: q1 = 1.09 nC, q2=0.93 nC, d1=2.49 cm, d2=6.9 cm, d3 = 4.27 cm. b. What is the direction of the electric field at the...
  44. C

    Mass point sliding down a sphere

    Homework Statement A mass point is sliding down from the top of a hemisphere, with an initial speed of zero. I want to determine the angle ##\theta## at which the mass point will lift off the surface of the hemisphere. Homework EquationsThe Attempt at a Solution We can determine the speed...
  45. Marrrrrrr

    A Virtual Fermions and Pauli Principle

    Hi guys, Do virtual particles, when they are fermions, obey Pauli exclusion principle as real fermions do? More specifically, what I am wondering is the following: Fermion fields would have some energy at every point in spacetime due to the uncertainty principle. Now, is it possible for the...
  46. T

    Is this point of contact an inertial frame?

    Consider a disc being pulled by a constant force F and it is performing pure rolling. Now, the disc has a certain acceleration, point A has a acceleration in right direction and another centripetal acceleration in vertically upward direction but it has zero instantaneous velocity because of pure...
  47. Conductivity

    Understanding Torque: Choosing the Point of Rotation for Rotational Motion

    I have a little bit of confusion here :c I don't understand something about torque. I can prove every definition about rotational motion if I assume that a point mass is moving in a circular motion. and if I also define a point of rotation I don't need an object to rotate in order to have...
  48. D

    Components of the equivalent moment at a point

    1. The problems: The questions are to find the x, y and z components of the equivalent MOMENT at point A in both diagrams. For the green block, I found the y and z components of the equivalent force at point A are -39.04kN and 15.48kN respectively. The Attempt at a Solution For the first...
  49. Epoch

    Electricity: electric field in a point Between Two Charges

    Homework Statement I've seen many books writing the cosine rule like this: a^2 = b^2 + c^2 - 2bc cos A My electricity textbook for an electric field in a point between two charges says this: E resultant = root[E1^2 + E2^2 + 2*E1*E2*cos(angle between E1 and E2)] In the first equation it is -2...
  50. M

    Finding electric potential given two point charges

    Homework Statement Find the potential at points P1, P2, P3, and P4 in the diagram due to the two given charges. Homework Equations VP =k∑qi/ri p = q ⋅ d The Attempt at a Solution I'm not sure how to approach the problem. I thought about using that given equation four times and adding it all...
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