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. chwala

    Find the car's speed at point when deceleration is increased - Mechanics

    Wawawawawawa! This was a tough one...:biggrin: Find the question below; Find my approach below: We have the following equations; 1. ##v=30-0.5t## 2. ##v=30-1.5t## Now the car changes its acceleration at some point i.e from ##-\frac{1}{2}## ##m/s^2## to ##-\frac{3}{2}## ##m/s^2## ... I...
  2. U

    COMSOL: Why does the prescribed displacement stop at a certain point?

    I have been experimenting in producing some strain to this object. However, after applying a prescribed displacement and setting it to a certain value, it does not exceed 2.18[um] no matter any extreme value for the prescribed displacement. I have also experimented with an applied force as well...
  3. T

    A Stationary Point of Variation of Action

    The action is the time integral of the Lagrangian - check. We take the variation of it, and set it to zero - check But how do we know it is a minimum and not a maximum? (Don't we formally have to deal with the second variation to be positive?) Or am I confused? Is it really just important to...
  4. F

    Engineering Find the electric field intensity due to a point, line, and plane

    Question: My attempt: Could someone please confirm my answer?
  5. F

    Engineering Finding the force acting on a point charge with a disk around it

    Question: Here's my attempt with the relevant equations: The correct answer is F = -99.4 az μN. Could someone please figure out my mistake?
  6. ZFurdzik

    Labelling a point on the x-axis with PGF-TikZ

    I'm confused about wrote a root of function when plotting here graph with pgf-tikz. Any help is welcome.
  7. D

    Linear speed of sphere as it passes through lowest point

    Let ##m_s = 0.05, m_{s_1} = 0.02, m_r = 0.12, L = 0.8.## be the masses of the two spheres, mass of the rod, and length of the rod. Then the work done by gravity when the rod reaches the vertical position is ##(m_s(L/2) - m_{s_2}(L/2))g## and the kinetic energy equals ##\frac{1}2 (\frac{1}{12}...
  8. S

    Tipping of a cabinet and determining velocity at a given point?

    I am trying to determine if there is a set of formula to calculate if a cabinet will when subjected to a force on it's upper edge for an angular distance (not a duration) will gain enough momentum to continue over the balance point and fall over or whether the opposing moment due to mass and...
  9. mcastillo356

    Calculus Where did my textbook say clearly what it states at this point?

    Hi, PF I left reading for a while, and now I must revisit a quote from Spanish 6th edition of "Calculus", by Robert A. Adams. The quote is " 4.2 Extreme values problems (...) As we've seen, the sign of ##f'## shows if ##f## is increasing or decreasing". Obvious, I shouldn't care and...
  10. P

    Equilibrium circular ring of uniform charge with point charge

    This is an offshoot of @Angela G 's thread. I don't want to hijack her thread so I decided to create a new one. Original thread https://www.physicsforums.com/threads/unstable-or-stable-electrostatic-equilibrium.1007881/ @kuruman @PeroK @bob012345 If you have the time I'd appreciate your input...
  11. B

    I Equation to graph a sine wave that acts like a point on a unit circle

    I need an equation to graph a sine wave that act like a unit circle but only positive numbers. so I need it to be 0 at 0, A at 90 , 0 at 180, A at 270, 0 at 360, and A at 450 and so on and so on... Now I know sin(0) is 0 in degrees and sin(90) 1 and I know if you Square a number is...
  12. N

    Engineering Find the velocity and angular velocity of the rod and point

    Hi everyone :)! I resolve this problem with components method and trigonometry method. My results with components method its okay, but i can´t obtain the correct VE velocity. Im sure that the problem its in the angles, but i don't know how to fix it. The correct answers: -Angular velocity...
  13. Mathman2013

    Find the coordinates of a point C from the given line, point and circle

    Let the point P(2,8) be a point in xy-plane and line m: y = -0.75*x+3.25 be a line in the xy-plan. The distance from a point P to a point B is 7 unites. Where the x coordinate of B is negative. Find the acute angle between PB and m. To find B I then construct a circle of radius 7 with center...
  14. Ugnius

    Thin Charged Isolated Rod -- Find the electric field at this point

    Hi , I've been trying to manage a solution in my head and i think I'm on the right path , i just need some approval and maybe some tips. So it's obvious I can't solve this without integration because law's only apply to point charges , and i can't shrink this object to a point as i could do with...
  15. A

    A What is the point of geometric quantization?

    I studied the basics of geometric quantization for a recent work in quantum-classical hybrid systems1. It was an easy application of the method of gometric quantization (prequantization + polarization in ##\mathbb{R}^{3}##). The whole topic seems interesting since I want to learn more of...
  16. Slipjoints

    Distance from a point on a circle to an arbitrary axis

    Hi all! In this assignment I have to formulate an equation for the shortest distance from a point on a circle perimeter to an arbitrary axis in a circle with angle theta. I included an image with the sketch. Anyone that can help?
  17. Rikudo

    Confusion in choosing an origin point for angular momentum

    I am currently reading David Morin book and found this statement : ##\,\,\,\,\,\,\,\,## "It is important to remember that you are free to choose your origin from the legal possibilities of fixed points or the CM" Is it really alright to choose the center of a...
  18. Mikasun1108

    What is the net force's direction of an object at its highest point?

    I'm not sure of my answer but it is e(downwards). I arrive at this answer since gravity always exists so no matter what happens it always pulls an object downwards. But I am not sure. Thank you -sun1108
  19. B

    Name or Label for the outer most point of a rotating object

    Hey all, I can't seem to find the answer anywhere, I'm not sure if I'm asking the right question though, if the name or label "Pivot" describes the rotational axis of an object is there a term or label used to describe the outer most point of the rotation?
  20. M

    Variance of a point chosen at random on the circumference of a circle

    Hi, I was looking at this problem and just having a go at it. Question: Let us randomly generate points ##(x,y)## on the circumference of a circle (two dimensions). (a) What is ##\text{Var}(x)##? (b) What if you randomly generate points on the surface of a sphere instead? Attempt: In terms of...
  21. V

    Electric field at a point within a charged circular ring

    I have broken the ring into a top arc and a bottom arc. First, let's assume an imaginary charge of +1 C is placed at point P. We will determine the force on this unit charge from top and bottom arcs. The charges in the top arc will result in electric fields that will all cancel each other...
  22. S

    Checking nature of turning point of parametric equation

    I have found the turning point. I want to ask how to check the nature of the turning point. My idea is to change the equation into cartesian form then find the second derivative and put the ##x## value of the turning point. If second derivative is positive, then it is minimum and if the second...
  23. Eclair_de_XII

    What's the point of life? Struggling to find purpose and joy in daily existence.

    Nothing I do seems to matter anymore and it is becoming nearly impossible for me to take interest in the world around me.
  24. V

    B Voltage between the positive terminal of a battery and a point in the air

    If I connect a voltmeter with the positive terminal of a battery and leave the other wire hanging in the air, it won't measure anything since it's not a closed circuit. But if there was a way to measure the voltage between those two points, what would the voltage be? Or is this a meaningless...
  25. crudux_cruo

    B Torque applied by a continuous mass instead of point particle

    I came across this 'problem' when I was trying to think about how a torsion spring would apply torque in something like a miniature catapult. I understand that in the context of something like turning a wrench, we can find the net torque on the wrench by treating the hand applying the force as...
  26. D

    Potential outside a grounded conductor with point charge inside

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  27. F

    I How do point charges in a conductor move and stop?

    Let's speak in the classical context (non quantum). We assume that point charges move in a conductor following Newtonian mechanics. How do point charges move along the boundary of the conductor and how do they stop (equilibrium) in the end?
  28. J

    Sketch the Electric Field at point "A" due to the two point charges

  29. yucheng

    What's wrong? Electric potential of a point on a ring

    So I have a ring(red) of uniform charge ##\lambda## per unit length, and I want to calculate the electric potential at the origin (actually on any point of the ring). It is clear that the ring is given by the equation $$r=2 R \sin \theta$$, in polar coordinates, where R is the radius of the...
  30. uni98

    Electric field of wire and cylinder at one point in space

    I can calculate the fields generated by the cylinder and the wire but I don't know how to calculate their vector sum to evaluate it at point A. Cylinder field inside: ρR^2/2rε Cylinder field outside: ρr/2ε Field generated by the wire: λ/2πr I should break the fields into components but I don't...
  31. A

    The value of a Fourier series at a jump point (discontinuity)

    Greetings according to the function we can see that there is a jump at x=e and I know that the value of the function at x=e should be the average between the value of f(x) at this points my problem is the following the limit of f(x) at x=e is -infinity and f(e)=1 how can we deal with such...
  32. karush

    MHB -apc.2.1.06 crosses the x-axis at one point in the interval [0,1]

    $\tiny{APC.2.1.06}$ The graph of $y=e^{\tan x}-2$ crosses the x-axis at one point in the interval [0,1] What is the slope of the graph at this point. a, 0.606 b. 2 c, 2.242 d.2.961 e.3.747 [d] $\begin{array}{rll} \textit{given} &e^{\tan \:x}-2 &(1)\\...
  33. M

    Question about how to calculate the Resultant Force at this point

    Hello all Trying to solve this one, faced a dilemma if i should trasfer the 5N vector from third to first quadrat becuase it head is on the 0 axis ass opposed to the two other vectors. If it remains in third quadrant its components eouls be both negative, if transferred to first quadrant both...
  34. B

    I How to calculate the focal length and focal point of collimator?

    I wanted to calculate the focal length and focal point of the collimator. The collimator diameter is 3mm, and I wanted to focus on the 100-micrometre active area of the detector.
  35. M

    MHB Points of the surface with minimum distance to the point (3,0,0)

    Hey! :giggle: We have the function $$f(x,y)=(x-3)^2+y^2+(x-y)^2$$ and I have shown that at $(2,1)$ we have a minimum and so $f(2,1)\leq f(x,y)$ for all $(x,y\in \mathbb{R}^2$. I did that in this way: I calculated the gradient and set this equal to zero and found that the only critical point...
  36. yecko

    Vaporization latent heat vs boiling point

    answer is 78oCdelta G = delta H - T delta S -235,310- (-277,690) = -38.56e3- T (282.59-160.70) T = -664K I am not sure if my concept is correct. May anyone help a little bit on that please? thank you
  37. S

    Point charge near charged plate

    I thought the equation listed should be used, with the 'charge density' determined by the point charge multiplied by the area of the plate, but not sure if that makes sense.
  38. I

    Vectors - finding coordinates of collision point

    For car 1, the parametric equations are x = 1 + 0.8t and y=t. For car 2, the parametric equations are x=0.6s and y=2+s. (Let t and s represent time). Solving the system of equations, when the x values are equated are the y values are equated, I get s = -13 and t = -11. I assume that the 2 cars...
  39. Eclair_de_XII

    B Proving the Existence and Value of a Derivative at a Point

    This proof has three steps and is very similar to (if not the same as) that other proof I posted here.(1) Prove the existence of a ball centered around ##a## with the property that ##f'## evaluated at any point in the ball is positive. (2) Prove that the right end-point of this ball is bounded...
  40. S

    Around which point does an aircraft rotate during the landing flare?

    Without giving possible options, as to not lead people in a wrong direction perhaps, I have a question I am struggling with. Mostly because I get different answers from different people 🤔 When an aircraft is coming into land and starts the landing flare, around which point does it rotate? It...
  41. silverrahul

    B Force between 2 Point Charges Across Frames

    So, i was trying to calculate, the net force between 2 point charges in their rest frame, and in a frame where they are moving. So, assume, there are 2 point charges each of charge +q. They are r distance apart from each other and moving parallel to each other with a speed v relative to a lab...
  42. G

    To find the tipping point of a lamina

    Could I please ask for help with the following: ABCD is a uniform square metal plate of side 3m. Points E and F are taken on AB and BC respectively such that BE = BF = x m and the portion BEF is removed. 1) Find the distance of the centroid of the remainder from AD 2) Show that the remainder...
  43. jaumzaum

    The Draper point and why can't we see human radiation

    I was wondering how many visible photons humans emit in a day. I did all the calculations with the Planck's Law (it's quite easy, because in the visible spectrum and for temperatures above 0 degrees the exponential term is much larger than one, and the "-1" can be taken out of the integral...
  44. H

    Finding (C): Halfway Between Equilibrium and End Point

    I think (D) is correct since it is half way between the equilibrium point and and the end point of its motion, it is a quarter of the total distance. How to get (C)?
  45. wrobel

    I Rigid body with fixed point

    Today I read a book in mechanics and encountered a funny proposition about rigid body with fixed point. Perhaps somebody will be interested to propose it to students as a task. This proposition is almost correct:) Consider a rigid body with a fixed point ##O##. Let ##Oxyz## be a coordinate...
  46. MathematicalPhysicist

    A Multi-Monopole Point of ##SU(N)## ##\cal{N} = 2## Gauge Theory in Four Dimensions

    I want to find the email of the authors. The problem is I cannot find hers. How to find it? Any help? Thanks in advance!
  47. Pipsqueakalchemist

    Engineering Zero Velocity & Acceleration of Point of Contact: Problem Explanation

    For this question the ball is rolling without slipping so that means the velocity of the point of contact is zero. Does that also apply to the acceleration of the point of contact? Because that’s what I assumed and I applied the relative acceleration formula above and use the starting point to...
  48. Pipsqueakalchemist

    Engineering Crate lowered by two ropes and deceleration at each point of contact with rope

    For this question, I don’t understand the steps for the relative motion part. When I try it I get angular acceleration to be zero which is obviously wrong. The solution doesn’t consider the Y distance between G and A but I don’t understand why. In the relative motion equation it’s suppose to be...
  49. Hamiltonian

    Calculation of the field due to a dipole at an arbitrary point

    I know how to derive field using ##E = -\nabla V## in polar coordinates and doing so gave me $$E = (kP/r^3)(1 + 3cos^3\theta)^{1/2}$$ now I am trying to derive ##E## at point P using the fields produced by +ve and -ve charge respectively and taking components of each along the radial direction...
  50. yucheng

    Where is the equilibrium point of a mass sliding down slacking cord?

    My two questions: The author claims that ##T_1=T_2## and ##\alpha = \beta##, and this is supposed to be clear the force triangle. Why is this so? Is it possible to use calculus of variation to find the lowest point C? That is, by maximizing the triangle ABC (Area of ABC = ##\frac{1}{2}(line...
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