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. E

    Is freezing point always depressed by a solute?

    Homework Statement Is the freezing point always depressed by a solute even if solute-solvent interactions are stronger than solute-solute and solvent-solvent interaction? What about amorphous solids? 2. Relevant knowledge According to my chemistry teacher's powerpoints, the freezing point is...
  2. L

    Determining boiling point from vapour pressure

    Homework Statement When benzene freezes at 5.5 C its density changes from 0.879 g cm-3 to 0.891 g cm-3. Its enthalpy of fusion is 10.59 kJ mol -1. Estimate freezing point of benzene at 1000 atm Homework Equations Solid liquid boundary: p=p*+ΔHfus/ΔV ln(T/T*) The Attempt at a Solution From the...
  3. C

    At what point is the system in equilibrium?

    Homework Statement This is more of a math question but: There are two particles fixed in place: a particle of charge +8q at the origin and a particle of charge -2q at x=L. At what point (other than infinitely far away) can a proton be placed so that it is in equilibrium Homework EquationsThe...
  4. TheMathNoob

    Find a line in the rectangle from 0.0 to some point

    Homework Statement There is a rectangle in the x-y plane with dimensions H=1, L=2. Find a line or diagonal in the rectangle in which for every point in the shaded area below that line x>y. Homework EquationsThe Attempt at a Solution The line has to intersect a point in y=1 in which x>y. This...
  5. M

    Summing moments about a point (statics)

    Homework Statement Hi, I don't have a specific problem, I just need to know what to do when summing the moments about a point if there is a moment given at a different point. Do I just add it into the equilibrium equation as if it was about the point I am summing the moments about? Homework...
  6. UMath1

    Boiling Point of Rubbing Alcohol Lab | In-Class Experiment

    In class, we did a lab to determine the boiling point of rubbing alcohol. We used a thiele tube filled with water and place a test tube attached to a thermometer w/rubber band in it. However, we never saw any signs of boiling. We conducted several trials, the temperature went all the way above...
  7. P

    Why is 1/3 considered a number line point when .333.... isn't

    Why is 1/3 considered a number line point when the decimal expansion never seems to stop at a point (if this is indeed the case)?
  8. W

    M2 Point C Moment Calculation: Why is it Not the Same as Book?

    Homework Statement for M2 , if i take the moment at pont C , then my ans would be (0.3i) x ((125X(3/5) j +125(4/5) k )= 30j +22.5k Which is not same with the book which use moment about D . why ? Is the value at the triangle at te upper part incorrect (circle part) ? Homework EquationsThe...
  9. W

    Finding the point where the line of action intersect with r

    Homework Statement I'm having problem of finding the point where the line of action intersect with CD , hot to do it ? Fx = -500cos60 - 250(4/5) Fy = 300 + 500sin60 + 250(3/5) FR = 991N Homework EquationsThe Attempt at a Solution
  10. G

    Direction of resultant force from a point

    Homework Statement I managed to get Fy = 900N , Fx = 200N and FR= 922N , how to get the distance from A is 3.56m ? tetha= arc tan (922/200) = 77.5 degree Homework EquationsThe Attempt at a Solution
  11. W

    Car accelerated by repulsion of two point charges

    At the outset, I want to explain that this is a problem I came up with myself. It's not actually homework, and I suspect it is deeply conceptually flawed in some manner that I have yet to determine. 1. Two point charges of like polarity, ## q_1 = q_2 = 1C ##, start out separated by distance ##...
  12. E

    Magnetic field strength at point P around a solenoid

    I have a solenoid, Length L, number of turns N, ampers I Radius R I have a Point P(x,y,z) anywhere around said solenoid. How can I calculate the field strength at point P, note it is OUTSIDE the solenoid, and could be anywhere outside. Assume the origin is the center of the solenoid, let's...
  13. C

    Electric Field Between Three Point Charges

    Homework Statement 1. Compute the electric field vector at the position of charge B for the case where q_{A}=4q_{C} and r_{1}=2r_{2} 2. Suppose that all three charge are positive and that q_{A}=4q_{C} . Consider the case where f q_{B} is moved to the right by a distance dr. Now r_{1} = 2r+dr...
  14. G

    Finding Stationary Points of a Function

    Homework Statement the critical point is the point which the f'(c) = 0 or f'(c) = doesn't exist . How if I'm asked to find the stationary point . In this question , the critical point is x=0.071 , -14.071, 3 , and -2 So, if i am sked to find the stationary point , it should be only x=0.071 ...
  15. gracy

    Conditions for neutral point to exist

    I want to verify whether I am correct .As the title suggests It is about point where potential is zero (point other than infinity) Note:x is distance of neutral point from charges Firstly,I would like to ask Is coordinate system necessarily be there 1) If there are two positive charges for the...
  16. K

    Angular momentum about inconvenient pivot point

    A rod of length L and mass M is rotating with angular velocity w about its center of mass. What is its angular momentum with respect to a rotating point 1/4L from the rod's end? What about a stationary point? Homework Equations With the respect to the center of mass, angular momentum L = Iw =...
  17. gracy

    How to find potential *Energy* between two point charges?

    How to find potential ENERGY between two point charges?I know how to find potential difference between two points and I also know how to find potential at any point . potential difference between two points 1 and 2 is simply ##V1##-##V2## potential at any point r=V While source charge is Q...
  18. Mike Dacre

    Mixed Melting Point of Two Pure Solid Crystals

    I understand why an impure solid will have a decreased melting point, however, in my recent organic chemistry lab section I mixed two finely ground pure solids together and observed that the mixture melted at a lower temperature than either pure solid. I understand this in principle, but...
  19. W

    Moment about a point using graph paper

    Homework Statement the ans given is 95Nm , but i gt 80.9Nm , which part i did wrongly ? Homework EquationsThe Attempt at a Solution 20(4) -39(5/surd 26(3)) +39(1/surd26)(1) -60(3/5)(1)+60(4/5)(3) =80.9[/B]
  20. W

    What is the Correct Magnitude of P in a System of Forces?

    Homework Statement In this question , I'm asked to find the magnitude of P . Homework EquationsThe Attempt at a Solution Resultant moment about O = -10cos30 (4√3) -10sin 30 (10 +15sin30(2) + 15cos30(4√3) -10cos30(4√3) -10sin30(4) -15cos30(4√3) -15sin30(7) +10cos30(4√3) +10sin30(11) +P cos...
  21. C

    MHB Find the point on the plane x − y + z = 8 that is closest to the point (1, 3, 6).

    Find the point on the plane x − y + z = 8 that is closest to the point (1, 3, 6). This what I have so far Z = 8-x+y d = Sqrt ((x-1)2 + (y-3)2 + (z-6)2) f(x,y,z) = d2 = (x-1)2 + (y-3)2 + (z-6)2 Substitute for z = (x-1)2 + (y-3)2 + (2-x+y)2 Not sure how to move forward...
  22. A

    Zero dimensional point particles?

    All elementary particles, which are not made up by any other particles (electrons, quarks), are said to be zero dimensional and have no size. But why not? Are electrons literally zero dimensional particles with no size?
  23. T

    Why Is the Photon One-Point Function Zero in QED?

    In 'an introduction to quantum field theory' by peskin, he writes: To analyze the photon one-point function, note that the external photon must be attached to a QED vertex. Neglecting the external photon propagator, this amplitude is therefore: I really cannot justify this equation. Can...
  24. G

    Moment at a point when the object is sliding

    Homework Statement i can't understand why when the total moment at B is positive , the object is not sliding ? can someone help to explain ? Homework EquationsThe Attempt at a Solution
  25. N

    Finding the time and maximum height at highest point

    Homework Statement :[/B] A projectile is given initial velocity 80 m/s ( V0 ) at angle 60° above the horizontal. Find the time it takes to reach to the highest point and find the maximum height. (g = -10 m/s2) Homework Equations :[/B] 1. y_{final} = y_{initial} + v_{y_{initial}}t + \frac...
  26. J

    Tension at the lowest point of a hanging chain

    Homework Statement Chain of mass M hangs between 2 walls with its ends at the same height. The chain makes an angle θ with each wall. Find the tension at the lowest point of the chain. a) By considering the forces on half of the chain. b) By using the fact that the height of the chain is...
  27. C

    What is the point of the elif statment?

    What's the point of the elif statement? Why not just keep the if and else statements and leave it at that? Can't the if statement be replaced with just if? Thanks.
  28. not_waving

    Electric field of a sphere in a point A

    My first homework for electrostatics course I'm taking is to find the vector of electric field of a completely hollow sphere (radius r, surface charge density σ in a point A, by integrating the electric field through the whole sphere. I already figured out the electric field of a ring in a point...
  29. E

    [Multisim] Transient time point calculation did not converge

    Hi. I have problem simulating this circuit in Multisim: (LTSpice) Here is scheme from Multisim: When I run transient analysis, I got this: ------ Checking SPICE netlist for Design3 - Saturday, September 26, 2015, 10:58:03 AM ------ ======= SPICE Netlist check completed, 0 error(s), 0...
  30. G

    Can Torque Be Applied to an Object Through Linear Forces Alone?

    Homework Statement Why the moment isn't=15* 3Nm? Since we are taking moment about point O...it's 3m away from O Homework EquationsThe Attempt at a Solution
  31. yango_17

    Potential for a charged ring and point charge system

    Homework Statement A ring of radius R lies in the x-y plane with the center at the coordinate origin. The ring is uniformly charged with with a uniform charge density +λ. a) Charge +q is brought along the z-axis from -∞ to the center of the ring. What is the increase in total potential energy...
  32. A

    Finding the coordinate of a point by Law of Cosines/Sines

    Homework Statement A model for the suspension of a vehicle is shown where the spring has stiffness k = 178 N.mm and an unstretched length of 347 mm. Here is the picture: http://i.imgur.com/1dTVs12.jpg Part a asked to determine the value of P and the force supported by member AB so that the...
  33. A

    MHB In the triangle ABC the point D lies on the side BC and point E on the side AB

    In the triangle ABC the point D lies on the side BC and point E on the side AB. BD = AC, AD = AE and AB ^ 2 = AC * BC. Show that \angle BAD = \angle CEA
  34. D

    Calculating Moment & Horizontal Force at O for 100 lb Force

    Homework Statement A 100 lb vertical force is applied to the end of a lever, which is attached to a shaft at O. Determine (a) the moment of the 100 lb force about O (b) the horizontal force applied at a that creates the same moment about O. Homework EquationsThe Attempt at a Solution I know...
  35. C

    Significance of the angle theta at r=0 point

    Hello, I was working on a classical mechanics problem, and I suddenly came up with this question: Let's think about a point in a 2-D plane. This point is represented by (r, θ), where r is the distance between the origin and the point and θ is the angle measured from the x-axis. Now, what is...
  36. Samuel Williams

    Does T have a unique fixed point in X?

    Let (X, d) be a complete metric space, and suppose T : X → X is a function such that T^2 is a contraction. [By T^2, we mean the function T^2 : X → X given by T^2(x) = T(T(x))]. Show that T has a unique fixed point in X. So I have an answer, but I am not sure whether it is correct. It goes as...
  37. C

    MHB Find the curvature at the point

    Find the curvature at the point (2, 4, −1). x = 2t, y = 4t3/2, z = −t2
  38. R

    Resistance between two point voltages on infinite plane

    Hi What would be the mathematical approach for calculating the resistance between two close points on an infinite plane of resistive material? And if the plane was circular/square/rectangular with the two points at the cente?
  39. raining Pete

    Algebra Help: Solve Trig for x, y with Point of h Base

    Hello all, was wondering if you fine chaps / ladies could help with a bit of algebra. Annoyed it's had to come to this but alas my algebra levels keep leading me astray. ## x + y = c ## ## x^2 + h^2 = a^2 ## ## y^2 + h^2 = b^2 ## I've been reading Measurements - Paul Lockhart (wish i picked...
  40. J

    Work moving point charge from center of conducting shell

    Homework Statement A point charge q is at the center of an uncharged spherical conducting shell, of inner radius a and outer radius b. How much work would it take to move the point charge out to infinity (through a tiny hole drilled in the shell)? [answer: q2/8πε0)(1/a - 1/b) Homework...
  41. P

    Velocity of point rotating on a wheel as the wheel moves

    Homework Statement So I have to prove that the total velocity of a particle on a wheel is Vcm+Ui=Vi where Ui is the particles velocity if the wheel's center of mass wasn't moving so just v=omega*R I'm assuming and Vcm is the velocity of the center of mass and Vi is the total velocity of the...
  42. T

    T-dependence of heat of vaporization near critical point

    The Wikipedia page on the heat of vaporization has a nice graph showing the heat of vaporization going to zero at the critical points of various substances. Is there a known form for the heat of vaporization as a function of temperature near the critical point? I imagine it is probably a power...
  43. moenste

    Determine from the time / height graph the speed at point

    Homework Statement Determine from the left graph the speed at t1. Answer: Draw the tangent (right graph) at t1 and determine the slope. v = 1.4/0.30 = 4.7 m/s 2. The attempt at a solution The slope is (Y2-Y1)/(X2-X1). t1 coordinates are (0.24-0.25, 0). In order to get the answer I should...
  44. M

    Solving for Charge of Particles on X-axis

    Hello everyone. Hopefully someone would be able to help me with this problem. The question states: Two point charges qa = -12 micro coulombs and qb = 45.0 micro coulombs and a third particle with unknown charge qc are located on the x axis. The particle qa is at the origin placed so that each...
  45. O

    MHB Cauchy sequence in fixed point theory

    İn some articles, I see something... For example, Let we define a sequence by ${x}_{n}=f{x}_{n}={f}^{n}{x}_{0}$$\left\{{x}_{n}\right\}$. To show that $\left\{{x}_{n}\right\}$ is Cauchy sequence, we suppose that $\left\{{x}_{n}\right\}$ is not a Cauchy sequence...For this reason, there exists a...
  46. Max Matiauda

    Image formed from object at focal point of concave mirror

    The question posed: "An object is located to the right of a mirror that in concave in its [the object's] direction. If the object sits on the focal point of the mirror, what answer best describes the image formed?" Our class is united in the notion that as the rays would be parallel...
  47. K

    Finding the neutral point of two charges

    Homework Statement Two charges q1=+9c and q2+-1c are separated by 2m. Where is their neutral point? Homework Equations E = E(+) + E(-) E= k q/r^2 The Attempt at a Solution k q1/(2+x)^2 = -(k q2/x^2) When I solve for this equation I end up square rooting a negative number which would then...
  48. R

    Electric field at a point from an insulating shell

    Homework Statement An infinite line of charge with linear density λ1 = 6.9μ C/m is positioned along the axis of a thick insulating shell of inner radius a = 2.6 cm and outer radius b = 4.8 cm. The insulating shell is uniformly charged with a volume density of ρ = -656μ C/m3 1)What is λ2, the...
  49. Antonius

    Electrostatics (four equal point charges)

    Homework Statement Four equal point charges q = +22.4 μC sit at each corner of a square. What charge Q, in μC, must be placed in the center so all the charges are in equilibrium? Your answer must include the sign of the charge. Homework Equations F = q1*q2 * k / r^2 3. The Attempt at a...
  50. L

    Finding the electric field at point P between two charges

    Homework Statement Find the electric field (both magnitude and direction) at point P located between the charges q1 = -3C and q2 = +4C. Point P is 1/3 of the charges' separation distance from q1 and 2/3 of the charges' separation distance from q2. Homework Equations E = kq/d^2 Etotal = E1 + E2...
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