Point Definition and 1000 Threads

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. frostysh

    We must show that any point of this segment....

    (mentor note: moved post from non-homework forum, hence no template) The problem: We have a segment of the line, the endpoint of which is stocked to the Axes, different endpoints, to the different axes. This segment is moving. We must show that any point of this segment will have ellipse-like...
  2. ikihi

    What is the electrical potential at point P?

    Homework Statement Three point charges of +6.00 μC, +4.00 [/B]μC, and +6.00 μC are placed along the x-axis 0.200 m above the +4.00 μC charge as shown in the figure below. What is the electrical potential at point P (relative to infinity) due to these charges? Diagram...
  3. A

    Point of Reference for Conservation of Angular Momentum

    When analyzing the conservation of angular momentum of a particular system, should we use the same p.o.r. before and after or can we use different p.o.r.'s? As far as I know, we should always use the same reference, but sometimes I see several solutions that use different references in my...
  4. M

    Prove that there is a point equidistant from 4 other points

    Homework Statement This problem is taken from S L Loney Coordinate geometry exercise (ch 2)[/B] Prove that a point can be found which is at the same distance from each of the four points ## \bigg(am_1,\dfrac{a}{m_1}\bigg),\bigg(am_2,\dfrac{a}{m_2}\bigg),\bigg(am_3,\dfrac{a}{m_3}\bigg) ## and...
  5. ReidMerrill

    IR active vibrations and point groups

    Homework Statement In lab we synthesised cis and trans copper glycine and we have to use IR to differentiate the two so we have to figure out the number of IR active vibrations for each complex. It's been a year since I did anything with point groups so I'm not sure if I did it right. Homework...
  6. H

    The point at which 2 vehicles meet

    Homework Statement Car A stopped a traffic light, once it starts moving again it is located 330 m from car B which is traveling in the opposite direction at a constant velocity of 18 m/s. If car A accelerates at a rate of 3 m/s^2 where and after how long will the two cars pass each other...
  7. S

    A What is the charge neutral point?

    I have a question about definition of charge neutral point. I`m reading some article about trilayer graphene, and this term, charge neutral point, is used in the article. I googling this word, but I can`t find something which can tell me what it is. In monolayer graphene, what i found by...
  8. A

    Finding the distance(shortest) from a point to a plane

    Homework Statement assuming the point given is P(3,2,3) and the equation of the plane is 2x + y + 2z = 2, find the distance and the point Q which represents that point Homework EquationsThe Attempt at a Solution Okay so I think that OQ-OP = QP, which connects the two points and is the line...
  9. P

    Quick clarification/question on Electric Field at a point

    Homework Statement http://i.imgur.com/wBdUomo.png Another simpler way to ask the question is if the electrical potential at a point is zero, is the electric field at that point also zero? Homework Equations v = kq/r E=kq/r^2 F=qe The Attempt at a Solution http://i.imgur.com/wBdUomo.png...
  10. U

    B Light Bending on Single Point: What Happens?

    Say you have two stars, star A and star B, separated by a distance of x, and the light from star A went directly from A to B but was heading directly for the centre point of star B. If the light passed near star B then due to the mass the will bend, yet if it was to pass through (or try to) the...
  11. Albi Mema

    Forces between the dipole and a point charge

    Homework Statement We have an electric dipole with moment P=2*[10][/-5] pointing in x direction. What is the force experieced by dipole at origin when a point charge Q=3*[10][/-4] is located at (0.014 m ,0,0) Homework Equations 1. [E][/dipole]=(1/4π[ε][/0])(2p/r3) 2. p=qs 3. F=qE 4. τ=pEsinϑ...
  12. Ron19932017

    I Ionic bonding from a quantum mechanics point of view

    Hi all, I have a question about the quantum nature of ionic bonds. I know some ideas about molecular bonding which can combine two ground state of H atom to get a bonding state and an anti-bonding state which in the case of H2 molecules it correspond to the covalent bonding (sharing of...
  13. anorlunda

    Leaky Ballpoint Pens: Engineering Advancement

    I'm so old, that in 2nd grade school we still used ink wells, and ink dip pens. (And yes I did get whacked for dipping a girl's pigtail in the well.) But they were replaced by ballpoint pens, But ballpoint pens in the 50s were terrible. They leaked ink profusely. If my memory is right, leaky...
  14. N

    B Notion of a zero dimensional point particle?

    When we say a fundamental particle is 0 dimensional, is that literal or figurative? Is it physically possible that a particle has it's properties (like charge, mass) spread out in a finite volume, but can be "shrunk" to increasingly small volumes when we measure it?
  15. T

    Partial derivative stationary point

    Homework Statement Hi guys, I am having real trouble with the function 10ii) I can take the derivatives, but I feel like I am missing something, with what I have done. I set $f_x=0$and $f_y=0$ but really can't seem to find away to solve, i keep getting (0,0) which when I plug into wolfram it...
  16. H

    B Constriction at point b, effect on flow rate before constriction

    In the case of a kidney vessel from point a to point b(a-------------b), say we constrict point b and increase resistance. Would the flow rate be decreased before the constriction at b, or would the flow rate only be changed after the constriction. Thank you Physicsforums!
  17. M

    Difference Electric Field Strength Point Charges vs. Plates

    Why does the electric field strength on a straight line (E = k.(Q1/d12+Q2/d22). D1,2 = distance with respect to Q1,Q2) between two point charges vary with the location on this line while the field strength between two parallel plates which remains the same anywhere between the plates...
  18. L

    What is the electric field at this point?

    Homework Statement A charge -3.2 micro-coulombs is spread evenly throughout a rod of length (a). At a distance (b) from the rod, what is the electric field? a = 1.2 m b = 3.4 m So basically, you start at zero and then there's a line of charge horizontally to the right from 0 to 1.2 meters...
  19. G

    Resources for finding boiling point at other than 1 atm?

    I would appreciate it if someone could recommend something. I found a boiling point calculator by CalcTool but it doesn't seem that reliable.
  20. B

    Unit vector perpendicular to the level curve at point

    Homework Statement Find the unit vector perpendicular to the level curve of f(x,y) = x2y-10xy-9y2 at (2,-1) Homework Equations Gradient The Attempt at a Solution I'm not sure what it's asking. Wouldn't this just be the gradient of f(x,y) evaluated at (2,-1) then normalized? or am I missing...
  21. M

    Show plane curve can be described with graph @ tangent point

    Homework Statement Provide a complete proof that a regular plane curve γ : I → R2 can near each point γ(t0) be written as a graph over the tangent line: more precisely, there exists a smooth real valued map x → f(x) for small x with f(0) = 0 so that x → xT(t0) + f(x)JT(t0) parametrizes γ near...
  22. P

    I Winding number for a point that lies over a closed curve

    The definitions of the winding number, that I have found, do not consider the case in which the point lies over the curve. Is there the winding number undefined ? I'm interested in this issue because I'm writing an algorihm for polygon offsetting that as first step creates a row offset polygon (...
  23. tarkin

    Electric Field due to multiple point charges

    Homework Statement [/B] Derive expressions for the magnitude and direction of the electric field at point P and the potential at R. Charges Q1 and Q2 are both positive. Distance from Q1 to P is h, distance from Q2 to P is √2 h Homework Equations E = k q/r^2 The Attempt at a Solution I...
  24. P

    Electric field at a point affected by two charges

    Homework Statement (a) What is the strength of the electric field at the position indicated by the dot? (b) What is the direction of the electric field at the position indicated by the dot? Specify direction as an angle measured ccw from the positive x-axis. ##Q_{1} = 4.0 C## ##Q_{2} = 9.0...
  25. D

    NTC and comparator to detect temperature trip point

    In "The Art of Electronics" the following is said: "A comparator in a circuit is a handy device that switches its output according to the relative voltages at its two input terminals. There is a temperature sensing device, a thermistor, which decreases in resistance by about 4%/°C. So we’ve made...
  26. C

    Getting direction of force of two point charges on a third

    Homework Statement What is the direction of the force F on the -10 nC charge in the figure? Give your answer as an angle measured cw from the +x-axis. Express your answer using two significant figures. Homework Equations ##F = k\frac{Qq}{r^2}## The Attempt at a Solution I started by getting...
  27. M

    MHB Point (a, b) Reflected About Two Lines

    This question is found in the challenge section of the textbook. This is a two-part question. Like always, I am looking for steps or hints that will allow me to work out the math. 1. If the point (a, b) is reflected in the line y = 3x, show that the coordinates of the reflected points are as...
  28. M

    MHB Is there a way to view LaTex on a cell phone?

    Points P and Q are reflected in the line y = x to obtain points P' and Q', respectively. Does the distance from P to Q = the distance from P' to Q'? What's the set up here?
  29. Ron19932017

    I End point information in lagrangain variation principle

    In lagrangian variation we are trying to minimize the action S = ∫t2t1 L dt. Consider a simple case of free particle. Imagine In a world that everyone one only knows how to solve ODE, Using euler lagrange equation, one has d2x/dt2 = 0 , give that we know the initial position of particle in the...
  30. M

    MHB How Do I Find a Point on a Curve with a Specific Slope?

    Find a point P on the curve y = sqrt{x} such that the slope of the line through P and (1, 1) is 1/4. Must I use the slope-intercept formula here?
  31. M

    MHB Which point is farther from the origin?

    Which point is farther from the origin? (3, -2) or (4, 1/2)? I know the origin is the point (0, 0). This is the location on the xy-plane where the x-axis and y-axis meet. Can the distance formula normally used to calculate how far points on the xy-plane are from each other be applied here? If...
  32. M

    MHB How do I use the midpoint formula to find the coordinates of point C?

    The coordinates of A and B are A(-1, 2) and B(5, -3). If B is the midpoint of line segment AC, what are the coordinates of C? I know this question is connected to the midpoint formula. If so, how do I use the formula to find the x and y coordinates of C?
  33. F

    Maximum shear acting on a point

    Homework Statement Why we need to consider only 3 cases when we want to find the max positive shear ? Homework EquationsThe Attempt at a Solution IMO , We know that the max shear will only occur when the 67.5kN act on B , am i right ? There is no need to consider 3 different cases ...Or my...
  34. Andrew Bridges

    Idea for a ball point pen that makes dashed lines

    Ok. So while in my trig class, I had an idea for a ball point pen that, when writing, it has an automatic mechanism for making dashed lines. I mean to say, it lifts the ball point or obscures the path to create a perfect dashed or dotted line, or allows to draw a line of fixed length for...
  35. I

    Two moments around a point question

    Homework Statement We are given a diagram to which we need to make measurements of. There is a line Y which is 9.5cm long. At one end, point X, is a force of 6,500N going perpendicular to the line; at the other end is point J, which the line continues for another 4.5cm to point P which is the...
  36. Alfreds9

    Finding the acoustic point in a valley

    Hello, I have a practical problem, I'd like to find the "best" spot to hear sounds in a valley (forgive me if "acoustic point" isn't an appropriate term, I just couldn't come up with anything better and scrolling an acoustics text didn't help), or at least a non-blind spot (one which instead...
  37. michael879

    I Understanding Relativistic Ptcl Lagrangian: S1 vs. S2

    Can someone help me understand how the following two actions are related? S_1 = \int \left(-\dfrac{1}{2}mg_{\mu\nu}\dot{x}^\mu\dot{x}^\nu - U\right) d\tau S_2 = \int \left(-m\sqrt{g_{\mu\nu}\dot{x}^\mu\dot{x}^\nu} - U\right) d\tau Both of them lead to the correct geodesic equation as the...
  38. V

    Given Two Point Charges, Find the charge at Point 0 as x,y

    Homework Statement Two point charges are placed on the x axis. The first charge, q1 = 8.00 nC , is placed a distance 16.0 m from the origin along the positive x axis; the second charge, q2 = 6.00 nC , is placed a distance 9.00 m from the origin along the negative x axis. Photo shown by...
  39. S

    Torque and rotation around a fixed point

    This isn't a real homework problem (i.e. I made this problem up myself for my own purposes), but I figured this is the correct forum to post. 1. Homework Statement In the following figure we have two rods connected to each other, and the bottom rod is connected to the blue structure (G), and G...
  40. F

    First derivative 3 point forward difference formula

    Homework Statement Can someone explain why for the first derivative 3 point forward difference formula is 4f(x-h) - f(x-2h) ?? Homework EquationsThe Attempt at a Solution Why it's not f(x-h) - f(x-2h) ? Is there anything wrong with the notes ?
  41. karush

    MHB Smallest Distance $P(-8,4)$ to Line $y=6x$ at Origin

    $\tiny{231.12.3.63}$ $\textsf{ Determine the smallest distance between point P and the line L through the origin}\\$ $\textsf{$P(-8,4)$ L is $y=6x$ }$ \\ $\textsf{$\therefore A=6, B=-1, m=-8, n=4$}$ \begin{align*}\displaystyle d&=\frac{|Am+Bn+C|}{\sqrt{A^2+B^2}}\\...
  42. A

    Electric field at a point (point charge and semi-circle rod)

    Homework Statement A thin semicircular rod has a total charge +Q uniformly distributed along it. A negative point charge -Q is placed as shown. (Point C is equidistant from -Q and from all points on the rod.) *Image Attached* Let Ep and Er represent the electric fields at point C due to the...
  43. Alettix

    Point inside a tetrahedron with vectors

    Homework Statement As part of a longer problem: "Find necessary and sufficient conditions for the point with positionvector r to lie inside, or on, the tetrahedron formed by the vertices 0, a, b and c." Homework Equations I am not sure... vector addtion? The Attempt at a Solution I don't...
  44. B

    How volatile impurity affects boiling point of a liquid?

    I know that non volatile impurities increases the boiling point of a liquid. Does volatile impurity decreases the boiling point? How?
  45. F

    Why is θA L Included in the Moment Equation about B'?

    Homework Statement For the moment about B ' , why there is extra θA L behind ? 2. Homework Equations The Attempt at a Solution is that wrong ? I think there should be no θA L behind in the equation of moment about B '
  46. F

    Finding displacement at a point in truss

    Homework Statement For the circled part , how to get the +1.33 , -1.67 , +1 ? What are they ? Are they the µ ? Homework EquationsThe Attempt at a Solution What is µ ? How to get the value ? It's not stated in my book though
  47. F

    Exploring the Moment Generated by 0.8NB at Point A

    Homework Statement for the moment about A , why there 's moment generated by the forces of 0.8NB (circled part) ?Homework EquationsThe Attempt at a Solution I think it's not necessary to include the moment 0.8NB(4) because the d = 0.4m is not measured directly from point A ...it's measured from...
  48. cathal84

    Find the equation of a plane perpendicular to a line and goes through a point

    Homework Statement find equation of plane P that is perpendicular to line L which passes through the point (-2,-2,3) Homework Equations ... The Attempt at a Solution [/B]line L passes through the points (1,2,1) and (0,0,-3) I have worked out the parametric equations of line L to be x=1-t...
  49. anorlunda

    What Are the Implications of Indian Point's Closure for NYC's Energy Future?

    http://www.nytimes.com/2017/01/06/nyregion/indian-point-nuclear-power-plant-shutdown.html This is very big news for a power engineer like me. I thought I would share it on PF and explain what the engineering implications are. Indian Point's nameplate rating is 2083 MWe Power supply for the...
  50. A

    Effect of particle size on boiling point in solution

    Hello. Suppose you dissolve something in water. I know that the boiling point should increase because as the water boils the solute's entropy decreases, and the net entropy should increase. Now suppose, that I dissolve GI chlorides in the water. Each solution of the salt has the concentration...
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