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. D

    Why does the melting point of aspirin increase

    I used sailcylic acid and acetic anhydride to produce aspirin and preformed recrystalisation to purify the aspirin. I need to evaluate why I have a higher/lower melting point. In this case, the melting point was 143°C whereas the true meling point is 135°C. I thought one of the reasons my...
  2. Poetria

    Square wheel and the speed of the point

    Homework Statement Consider a bumpy road in which each hump has the shape ##y=\cosh(a)-\cosh(x)## for ##-a\leq x \leq a## where ##y'(a)=-1## so ##a=arcsinh(1)## L=2 ##(x_p(t), y_p(t)) = (t, \cosh(a)-\cosh(t))## ##(x_q(t), y_q(t)) = (t, \cosh(a))## We place the square wheel onto the bumpy...
  3. A

    Find the amount of work to move a particle from point A to B

    Homework Statement How much work should be done on a point charge of q=15 nC to bring it from infinity to a distance of 3 cm from a surface of a charged sphere? Diameter of sphere is 15 cm, its surface charge density is 12 microC/cm2 Homework Equations W=deltaU=q*deltaV v=kQ/r...
  4. A

    Point where the electric field is zero

    Homework Statement Charges q1= +3 nC and q2=+8 nC have a separation distance of d= 12 cm. Find the point where the electric field is zero. Homework Equations E=kq/r2 The Attempt at a Solution I approached this problem as follows: 1) I assume the point where it happens is between charges, on...
  5. Tomi Kolawole

    The potential difference between a sphere shell and a point

    I am to use this formula: https://d2vlcm61l7u1fs.cloudfront.net/media/fee/fee798ea-5480-47af-9904-35c76ac35e25/phpSzecLa.png I tried using intergral of (E*dr) as in the equation to integrate over the distance of V(2A)-V(0) But when i am to plug in zero into my integrate it would give a math...
  6. A

    I Integrating a Function over a Torus Contour

    I'd like to integrate a function over a closed circle-like contour around an arbitrary point on a torus and I assume I would use the expression: $$ \int_{t_1}^{t_2} f(x,y,z) \sqrt{x'(t)^2+y'(t)^2+z'(t)^2}dt$$ And I cannot come up with an explicit parameterization of the variables in terms of...
  7. radiant_june

    Electric field strength at a point between charges

    Find the electric field strength at point B between two charges shown below: Given/Known Values q1 = 4.0×10-6 C r1 = 40 cm = 0.4 m (Distance from q1 to point B) q2 = -1.0×10-6 C r2 = 30 cm = 0.3 m (Distance from q2 to point B) k = 9.0×109 Nm2/C2 Equations Electric Force: FE = (k⋅q1⋅q2)/r2...
  8. J

    MHB Equation to find an unknown point on a graph

    Hi All, I need help to find an equation that will give me the location of 'E' in the image below. 'A' is the starting point on a graph. All values from 'B' to 'D' are known values. Currently, 'B' = 50, 'C' = 20, & 'D' = 135° - but I need an equation that will find 'E' no matter what these...
  9. ?

    EM fields of two opposite moving point charges

    I wrote and solved this problem but am having serious doubts about the answer I obtained. Homework Statement Two point charges \pm q move along the z-axis with velocity \pm v. If they are at the origin when t=0, what is the electric field magnitude a distance r from the z-axis? Homework...
  10. P

    MHB Restricting Values in Desmos error (for a complicated parametric point).

    Hello. I have graphed a rose curve on Desmos using a parametric point, the equation looking like this: However, I want the graph to be limited so that only values within the circle r=3.45 and r=9 are shown. I have tried using the curly brackets {3.45 <= r <= 9}, however this returns an error...
  11. abrogard

    B What Is The Energy of a Point In Space?

    Please, moderator, just delete this question if it is too silly. I am wondering what is happening in anyone point in the SpaceTime field. That's what it is called, I think? Because my simple understanding is that we see colours/light because of propagated electromagnetic radiation at...
  12. C

    The net electric field at point A is 6.7x10^4Nm.

    Homework Statement Calculate the net electric field at point A. [/SIZE] Homework Equations Enet(total) The Attempt at a Solution [/B] The electric field at point A will due to charge 2 will point towards charge 2 because charge 2 is negative. The electric field at point A will due to charge...
  13. T

    Electric flux of a cube due to a point charge

    Homework Statement Homework Equations Gauss's Law The Attempt at a Solution I simply used logic and observed the symmetry of the cube. If the charge is placed on the middle of the cube, the flux would simply be Q/∈0. The face of the cube itself can be split into 4 squares, with the charge at...
  14. lc99

    What was the point of this prelab i just did?

    Homework Statement Homework EquationsThe Attempt at a Solution It seems like i was just trying to figure out the frequency by finding the slope, but what exactly is this of importance for?
  15. W

    MHB Solving Point Distributions for Negotiation Simulation w/Thresholds

    I'm trying to create a negotiation simulation and don't know how to find point allocations for each party that will allow agreement in only about 20% of the cases. Wondering whether anyone here would solve the problem for me. The point allocations I came up with allow agreement only a few...
  16. A

    Equivalent point charge, dipole, and quadrupole

    There is a big sphere with charges distributed on the surface. N charges are distributed on a patch of the sphere (all the information of the charges such as their locations are known). Suppose the rest of the sphere has similar charge distribution as the patch, how to approximately calculate...
  17. Nathan Warford

    B How Can Point Particles Have Cross Sections?

    This is a topic that I have tried researching and I have not been able to find any meaningful information about it. The standard model of particle physics describes particles as point-like objects with no spatial extent. What I can't wrap my head around is how true point particles can...
  18. G

    MHB Calculate third point from 2 points and an angle

    I'm having a hard time putting together a formula. I have 2 points (x0, y0) and (x1, y1) and an angle (k). Using this information I need to calculate a third point that is k degrees from the previous 2 points. Is it possible to do that? Thank you for your attention.
  19. MCTachyon

    Resultant force and its point of action

    Homework Statement A storage tank has the cross-sectional shape shown attached and is of 1m breadth. Calculate the resultant force acting on the inclined surface AB and its point of action. The density of the liquid is 900kgm–3 and take g = 9.81ms–2. Homework Equations P = ρgh F = ρA Point...
  20. amerikantech

    Linear equation, point slope conversion

    Homework Statement convert: Y − 200 = −4 (X − 15) to X = −0.25 ⋅ Y + 65. with a given Δy/Δx = -36/4 Homework Equations point slope, slope intercept The Attempt at a Solution I understand point slope, slope intercept, and standard form, I understand how to convert one to the other, but I...
  21. Humbleness

    Heat transfer, how long it takes ice to reach melting point

    Homework Statement A 0.25 kg piece of ice at -30 C is warmed by an electric heater and the following graph of temperature is produced. Assume that there has been no loss of energy to the surroundings. - Use the info on the graph to determine the power output of the heater - Explain how long...
  22. M

    Electric potential at an unknown point

    Homework Statement The electric field inside a parallel plate capacitor is measured to be E= -3500 N/C i. The electric potential at point XA = 3.00 m is measured to be 1500V. What is the electric potential at point XB = 0 m? Homework Equations V=E⋅s The Attempt at a Solution I think I need to...
  23. W

    The magnetic flux density at point P between parallel wires

    Homework Statement In the picture at points A and B are two thin parallel wires, where traveling currents are 15 A and 32 A to opposite directions. The distance between wires is 5.3 cm. Point's P distances from A and B are the same. Calculate the magnetic flux density at point P. Homework...
  24. Richie Smash

    What is the speed of block as it reaches O from point P

    Homework Statement A 0.5 Kg block slides from rest down an inclined plane as shown in the figure. The velocity at the bottom of the plane is 6 m/s. The vertical distance PO is 2m. (gravity = 10m/s2 If the block were to be dropped from P, what would be the velocity at O? Homework Equations K.E=...
  25. starstruck_

    Integral (Trapezoidal rule and mid point rule)

    Homework Statement find: ∫13e^(1/x) upper bound: 2 lower bound: 1 using the trapezoidal rule and midpoint rules estimate the errors in approximation Homework Equations I've done the approximations using the trapezoidal rule and midpoint rule, but I can't figure out how to calculate...
  26. HappyFlower

    Two beetles run across flat sand, starting at the same point

    Homework Statement Two beetles run across flat sand, starting at the same point. Beetle 1 runs 0.50 m due east, then 0.80 m at 30◦ north of due east. Beetle 2 also makes two runs; the first is 1.6 m at 40◦ east of due north. What must be (a) the magnitude and (b) the direction of its second run...
  27. Rigel84

    B At which point is gravity the strongest?

    I'm embarrassed to admit that I am bit confused with concept of gravity. Here is practical example: When I stand on surface of the Earth majority, actually all mass is bellow me and gravity pulls me down. Let's imagine now that I am standing on the Earths iron core, majority of mass is above me...
  28. D

    Effect of impurities on the boiling point of ethyl ethanoate

    After carrying out reflux and distillation to produce ethyl ethanoate (ethyl acetate) I measured the boiling point and I got 71 degrees Celsius whereas the true value is 77.1 degrees Celsius. Impurities increase the Boiling point (BP) as well as concentration. However my calculates BP is lower...
  29. M

    Find the point of intersection?

    Homework Statement Find the point of intersection of the following lines, if it exists. Homework Equations None. The Attempt at a Solution I think the first step is to form 2 equations, but I'm not too sure.
  30. M

    MHB Fixed point iteration: g is a contraction mapping

    Hey! :o We have the function $f(x)=x^5-\frac{5}{16}$. I have approximated the root of that function using three steps of Newton's method with initla value $x_0=\frac{1}{2}$ : \begin{align*}x_1&=x_0-\frac{f(x_0)}{f'(x_0)}\approx \frac{7}{5} \\ x_2&=x_1-\frac{f(x_1)}{f'(x_1)} \approx...
  31. Ignitia

    Position of two point charges

    Homework Statement "Can you arrange the two point charges q1 =−2.0×10−6 C and q2 =4.0×10−6 C along the x-axis so that E =0 at the origin?"Homework Equations E = K (|q|/r2) K = Coloumb Constant The Attempt at a Solution Since one particle is negatively charged and the other is positively...
  32. F

    Newton’s Laws and Point Particles

    Why are Newton’s laws often discussed as applying to point masses when Newton makes no references to point masses in the Principa. He seems to mention nothing other than bodies while describing each of his three laws, which are not necessarily point masses.
  33. G

    I Forces between point particles: Always towards or away?

    Hi. I've read the following argument why the torques generated by internal forces add up to zero: Since by Newton's third law all forces come in pairs, so do all internal torques, adding them we get...
  34. Benjamin

    Calculating Electric Field from Force on a Point Charge

    Homework Statement What is the electric field at a point when the force on a 1.20 µC charge placed at that point is = (3.0 î -5.0 ĵ) × 10-3 N? Homework Equations E = KQ/d^2 The Attempt at a Solution I'm having trouble visualizing the question. I attempted to draw it out, but its not making...
  35. Spinnor

    I Calabi-Yau manifold + ideal gas + point disturbance?

    Because it is a closed space, can it make sense to fill a Calabi_Yau manifold with an ideal gas and consider waves from a point disturbance? Would the Ricci-flat condition of Calabi-Yau manifolds have anything to say about possible sound waves? Thanks!
  36. SemM

    I What are the limits of the boundaries for the Schrödigner equation

    If one considers the quantized levels of E, for the solutions to the Schrödinger eqn,, then I am wondering: what are the lowest possible energies that can occur for the Schrödinger eqn? I take the highest possible energy is at the classical limit, but is the zero-point energy the absolute...
  37. Eclair_de_XII

    Prove that x is in S or x is an accumulation point of S

    Homework Statement "Let ##S## be a non-empty set of real numbers bounded from above, and let ##x=sup(S)##. Prove that ##x \in S## or ##x## is an accumulation point of S." Homework Equations Neighborhood: "A subset ##O## of ##ℝ## is a neighborhood of ##x\in ℝ## iff there exists an...
  38. F

    Point on the curve closest to (18,1)

    Question: Question: Find the point on the curve y=x^2 +1 that is closest to the point (18,1). Please see the image and that’s where I’m stucked- after taking the first derivate. Please solve it further step by step completely. It’d mean a lot.
  39. L

    Elastic Spring / Simple Pendulum Lowest Point

    Homework Statement A perfectly elastic spring swings in a vertical plane as a simple pendulum with a mass m suspended at the bottom of the spring. The force constant for this spring is ##k## and the unstretched length is ##L##. The spring is carefully held in the horizontal position so that the...
  40. lightest

    Point charge with grounded conducting planes angled 120

    Homework Statement The problem states: "A point charge q is located at a fixed point P on the internal angle bisector of a 120 degree dihedral angle between two grounded conducting planes. Find the electric potential along the bisector." Homework Equations ΔV = 0 with Dirichlet boundary...
  41. V

    Find the point when velocity is momentarily zero

    Homework Statement [/B] A block travels in the positive x-direction with some velocity ##v_0##. It is subject to a drag force $$F(v)=-F_0e^{Kv},$$ where ##F_0,\,K## are positive constants. Find the point in time when the velocity of the block momentarily goes to zero. Find how far the block has...
  42. I

    Bernoulli's Equation, Find gauge pressure at 2nd point

    Homework Statement At a certain point in a pipeline, the velocity is 1 m/s and the gauge pressure is 3 x 105 N/m2. Find the gauge pressure at a second point in the line 20 m lower than the first if the cross-section at the second point is one half that at the first. The liquid in the pipe is...
  43. S

    Find the electric field at the point 20cm above the centre

    Homework Statement Hi guys, I was hoping I could get some help on this question! The question: "Find the electric field at the point 20 cm above the center of the square made of 4 charged rods of L = 20cm and Q=1mc each. Homework Equations I believe E = (KQ)/r^2 is the only equation needed...
  44. TuanTran

    What is the Magnetic Field at Point O?

    Homework Statement Homework Equations Magnetic Field of a Current Loop The Field of a Long Straight Wire The Attempt at a Solution Sorry ! I'm so stupid that i couldn't figure a way to solve this exercise. I don't know how to start with those two equations. Please help me !
  45. U

    Testing floating point numbers for equality

    Anybody can help me?? The problem is when the value of (r1o = r, and r2o=r), the result will be infinite,,,what the the probably test for this case?? I can't test floating point numbers for equality ( if r == 0.5 and r == -0.5). But, when running this program without test floating point, it...
  46. Altair Tans

    Exploring a Universe with One Point Charge

    What if there is a universe with just one point charge in existence....just a charge with vast emptiness around it....now here all laws of physics remain same... But is the concept of field and energy defined there??
  47. K

    Uniform rotating rod about a point at one end of the rod

    Homework Statement A uniform rod (mass = 5.0 kg, length = 0.3 m; the rotational inertia of the rod relative to the axis through its centre of mass is I = (1/12) ML^2 ) is free to rotate about a frictionless pivot at one end. The rod is released from rest in the horizontal position. What is the...
  48. D

    Stargazing Programable telescope that will point to any spot on Earth?

    Is there a programmable telescope that will point to any spot on Earth from my location that I could simply plug in the latitude and longitude and it would point at the location anywhere on Earth. For instance, if I wanted it to point at the LHC (Large Hadron Collider), could I just plug in the...
  49. Pushoam

    Point charge outside a grounded conducting sphere

    Homework Statement Homework EquationsThe Attempt at a Solution Option (a), because the potential is 0 on the surface, and potential due to point charge is positive so there must be negative charge on the surface. Since opposite charges attract each other, there is an attractive force...
  50. F

    Current flowing from point A in a circuit to point B

    Homework Statement A current at point A of 2A flows through a resistor (3 ohms), a battery of 20V (negative terminal first), another resistor (1 ohm) and a battery of 6V (positive terminal first). What is the potential difference between A and B Homework EquationsThe Attempt at a Solution I...
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