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. karush

    MHB A particle traveling in a strainght line passes a fixed point O

    so if $a\left(t\right)=p+qt$ then $v\left(t\right)=\int a\left(t\right) dt = pt+\frac{q {t}^{2}}{2}+C$ if $v=3.5$ when $t=2$ then $1.75=p+q$ if so, now what? the answers are $4, -3; 4m$
  2. NihalRi

    The point of the Euler-Lagrange equation?

    When trying to come up with the geodesic equation for a sphere I came across this equation. My question, is this equation just a short cut so we don't have to integrate and differentiate with two variables. Here is the equation...
  3. A

    Can we apply Friss equation to find field strength at the receiving point....

    Can we apply friss equation to find field strength at the receiving point for space wave propagation?
  4. stvrbbns

    2D - What is the next point given this info.

    In a two-dimensional environment: Given: a starting point (x1,y1) an initial velocity (speed and 2D heading/direction) a constant rate of turning (yaw, since there is no roll or pitch in only two dimensions) a constant acceleration of the object from itself (not like gravity where the direction...
  5. W

    Solving Electric Field with 3 Point Charges: Find q1 & q2

    Homework Statement IF the resultant electric field at D due to the three point charges is zero, find the magnitudes of q1 q2 in terms of q [/B]...
  6. Marisabel

    The motion of the mass starting from its highest point t=1.3

    Homework Statement (a) A large spring has one end attached to the floor and a platform attached to its upper end. On the platform is placed a mass of 30 kg. The mass of the platform itself is 10kg. The spring-platform-mass system is then set into vertical oscillations with a period of 1.5 s...
  7. D

    MHB Calculus: Maximum point for revenue function

    Hello (Smile). I have been stuck on this question for a while. A company charges $550 for a transistor set on orders of 50 or less sets. The charge is reduced by $5 per set for each order in excess of 50 sets. Find the largest size order company should allow so as to receive a maximum revenue...
  8. N

    Voltage of a point in varying permittivity medium problem

    Homework Statement - A point charge is placed at the origin of the medium. - The relative permittivity of the medium, \varepsilon_r = a / r, a is a constant, r is the radius from origin to any point around the charge. - Objective of this question is to find the expression for voltage.at any...
  9. P

    Why did writers use ancient latin to make their point?

    whats so special about latin that they couldn't just make their point without using latin, especially because more people could understand their point? I have 2 ideas.. do either of them have any merit? 1. latin was used by the educated people so they could exclude not so smart people from any...
  10. P

    Finite Size vs Point Size Hydrogen like Atoms

    Ok my question: what is the difference between the binding energies of these 2 types of atoms, conceptual wise, which one is greater? I am assuming based on the easy calculations of the potential energy of the finite size atom ( inside and outside) There is a difference between the potential...
  11. ShayanJ

    Three point charges inside a conducting spherical shell

    Homework Statement There are three point charges inside a conducting spherical shell of radius R. One of them of charge -2q is in the origin and the other two with charge q are in z=d and z=-d. Find the potential inside the sphere! Homework Equations ##\nabla^2\phi=4\pi \rho## 3. The attempt...
  12. ELiT.Maxwell

    Point charge inside a electrically neutral cavity in conduct

    bear with me, i know that this question has been asked many time , but i would like a definite answer, now, starting off the external charge density on the outer surface of sphere WILL be uniform by unique solution of Laplace equation and letting the sphere be huge, so, electric field due to...
  13. K

    Does Loop quantum gravity have an effective UV fixed point?

    loop quantum gravity and loop quantum cosmology gravity becomes weaker then repulsive instead of stronger, towards the Planck regime, due to the onset of quantum effects. gravity near Planck energies and densities, LQG/LQC becomes repulsive. at the inflection point where LQG gravity strength...
  14. T

    Help Me Understand This Author's Point: Noether's Theorem

    I don't understand how the author get to these point. Please help me as i have been spending so much time trying to figure this out but to no avail. Thanks for your help Source: http://phys.columbia.edu/~nicolis/NewFiles/Noether_theorem.pdf
  15. M

    Interpreting derivatives at a point

    Homework Statement How should I interpret the derivative of the following function at C=6% ##N = \frac {I} {C} - D##Homework Equations ## \frac {dN} {dC} = \frac {-I} {C^2} ## At I =12 and C=6%, I am getting ## \frac {dN} {dC} = 3,333 ## I am not sure what to make of this large number. I...
  16. PcumP_Ravenclaw

    Tangent at a single point?

    Halo, my question is what is the shape of a single point? Is it round? When we find the tangent line it is in relation to the surrounding points around the point of interest. For a circle tangent line is line that cuts through a single point only but in a parabola this cannot be true because the...
  17. P

    Magnitude of the Magnetic Field at point P

    Homework Statement Two long wires (in cross section) that each carry a current ##i## directly out of the page. What is the magnitude of the field at point ##P##, which lies on the perpendicular bisector to the wires? Homework Equations ##B_{wire}=\frac{\mu_0 i}{2\pi r}## The Attempt at a...
  18. Carson Birth

    Motion of a point mass (circular motion)

    Homework Statement A point mass, sliding over an even, horizontal plane is bounded on an inextensible, massless thread. During the motion, the thread is pulled by a force F with constant velocity ##v_{o} ## through a hole O. In the beginning (##t_{o} ## = 0) r(##t_{o} ##)=b holds (the length...
  19. RicardoMP

    Fixed point method for nonlinear systems - complex roots

    Homework Statement I've been asked to graphically verify that the system of equations F (that I've uploaded) has exactly 4 roots. And so I did, using the ContourPlot function in Mathematica and also calculated them using FindRoot. Now, I've to approximate the zeros of F using the fixed point...
  20. S

    Calculate force on point charges

    Find the force on 2Q and -Q/22. Force between two point charges is given by : F = k.q1.q2 / d[2][/SUP]The Attempt at a Solution To find the force on 2q, I added the charges on left side and then calculated it using the formula. But how do we do it for -Q/2. Please guide me. Thanks
  21. G

    Black holes' existence from our point of view

    Hi, layman here, I have often read that because of time dilation, we would never see any infalling matter actually crossing the event horizon, it would just look more and more redshifted towards becoming invisible, even for infrared or microwave / radio detectors, but never becoming part of the...
  22. S

    Find the value of point A and B

    Hello experts. I am attaching the image below. Kindly tell me how to calculate the values of A and B in the given figure? Now I must find A and B. How to get it? PS: P=-2.5+4.33i. But A is not at -2.5. Means PA is not making angle 90 with real axis. Thank you
  23. N

    Quescent point and ac and dc load lines

    Can anyone explain me in simple words what is quescent point and what is shows 2- what is ac and dc load lines what they represents actually and what is difference between ac and dc load lines
  24. W

    In which direction does static friction point?

    As I see it; static friction is what provides the centripetal force, but does it do anything else? When the brother applies tangential force, what will happen with the static friction, because I assume it will start to provide less centripetal force because the tangential speed of the child...
  25. Titan97

    Electric field due to point charge on an infinite metal plat

    If there is a small object with positive charge placed above a metal plate, the object induces a negative charge on the surface of the plate facing the object. Let's call this surface as S1. (The metal plate is initially uncharged). But from conservation of charge, the net charge in a metal...
  26. 0

    Acceleration of Rest Point for Rolling without Slipping

    Let's ignore gravity in this problem for simplicity. For a wheel rolling without slipping on some surface, the rest point is the point at a given instant of time that is in contact with the surface (the rest point has zero instantaneous velocity). If the wheel is rolling at constant velocity...
  27. vetgirl1990

    Finding radial & tangential acceleration at a point

    Homework Statement A point on a rotating turntable 20.0cm from the center accelerates from rest to final speed of 0.700m/s in 1.75s. At t=1.25s, find the magnitude and direction of (a) the radial acceleration, (b) the tangential acceleration, (c) the total acceleration of the point. Homework...
  28. A

    4 point support beam reactions calculator

    Hey guys, I am developing an program for calculation of reactions in a "4 point support beam". The problem is that this structure is Statically indeterminate and hence requires some other method. Support on any level is appreciated, especially from Civil Engineers. I will keep on posting...
  29. evinda

    MHB The distance is attained by a unique point

    Hello! (Wave) Theorem:Let $K$ be a convex and closed subset of a Hilbert space $X$ and $x \in X$. Then there is a unique $y_x \in K$ such that $$||x-y_x||=d(x,K):=inf \{||x-y||: y \in K \}$$ Remarks: - if $K$ is not closed then the distance $d(x,K)$ isn't attained in general. If for example...
  30. 0

    Lack of Orientation of a Point Mass

    The point mass (aka particle) is a fictional but useful concept. However, I have yet been able to find a definition of what exactly a point mass is. It is commonly accepted that a point mass does not have an orientation, and thus only 3 coordinates to determine its position are required (as...
  31. A

    Normal of a point on an ellipse

    Homework Statement 11) The tangent at P on the ellipse \frac{x^2}{a^2}+ \frac{y^2}{b^2}=1 meets the x and y axes at A and B. Find, in terms of the eccentric angle of P, the ratio of the lengths AP and BP. 12) Repeat Question 11 using the normal at P. Homework Equations bx \cos \theta + ay...
  32. J

    What is electron? Is it a perfect point? What does it mean?

    Electron is usually imagined as a simple point charge, but in fact it is a very complex entity: https://dl.dropboxusercontent.com/u/12405967/electron.png - being electric charge itself means singular(-like?) configuration of electric field - E behaves like 1/r^2, - it is also magnetic dipole...
  33. Z

    Proof: A point is a limit point of S is a limt of a sequence

    Hi guys, I attempted to prove this theorem, but just wanted to see if it a valid proof. Thanks! 1. Homework Statement Prove that x is an accumulation point of a set S iff there exists a sequence ( s n ) of points in S \ {x} that converges to x Homework Equations N * ( x; ε ) is the x -...
  34. I

    Question about electric potential at a point

    Homework Statement Three equal charges are equidistant from point Z. What is the electric potential at point Z? Homework Equations V = kq/r The Attempt at a Solution Because the charges are equal and equidistant from point Z, would I find the electric potential by: V = (3kq)/r ? Thank you!
  35. noowutah

    Stationary point for convex difference measure

    Let \mathbb{S}^n be a simplex in \mathbb{R}^{n+1}, so \mathbb{S}^{n}=\{x\in\mathbb{R}^{n+1}|\sum{}x_{i}=1\}. Let D be a difference measure on \mathbb{S}^{n} with D(x,x)=0 and x=y for D(x,y)=0. D is also smooth, so differentiable as much as we need. Let (R) be a convexity requirement for D...
  36. V

    MHB Break-Even Point: Manufacturing Company Analysis

    A manufacturing company is studying the feasibility of producing a new product. A new production line could manufacture up to 800 units per month at a cost of \$50 per unit. Fixed costs would be \$22,400 per month. Variable selling and shipping costs are estimated to be \$20 per unit. Market...
  37. Z

    Interior Point of 1/n

    Hi All, A simple question but one for which I cannot seem to get the intuition. 1. Homework Statement Find the interior point of {1/n : n ∈ ℕ}. Homework Equations N/A The Attempt at a Solution Let S = {1/n : n ∈ ℕ}, where S ⊆ℝ x is an interior point if ∃N(x ; ε), N(x ; ε) ⊆ S. My...
  38. gracy

    Potential V at point P on the axis of the ring.

    Homework Statement Electric charge Q is uniformly distributed around a thin ring of radius "a".Find the potential at a point p on the axis of the ring at a distance x from the centre of the ring. Homework Equations ##r##=##√x^2+a^2## The Attempt at a Solution \ [/B] I just want to ask...
  39. ScepticAmatuer

    Boiling point of water heated via microwave

    I took about 100 ml of distilled water, put a small, clean rock in it (to prevent "bumping" or explosion) and heated it repeatedly in a microwave oven on high for 45 seconds. After each heating I checked the temperature of the water with a digital temperature probe. I did this 7 or 8 times...
  40. A

    System of lenses with a light source at first focal point

    Homework Statement So I have this system of lenses with this problem: First lens: focal length ##f_1=50 mm## Second lens : focal length ##f_2=400 mm## Distance between them ##d=600mm## A small light source is placed at the focal point for the first lens. At the focal point for the second...
  41. L

    Tension in string at a point on a frame

    Homework Statement Hi all. What concerns me here is that it's worth 10 marks, but the solution I've tried only takes 2 steps. Am I missing some relation between the frame support and the pulley altering the components of the tension, or is the solution really just a basic trig conversion...
  42. R

    Biology Point mutation, change in rna and protein

    Homework Statement UV Rays is said to induce point mutations which get incorporated during the DNA replication process. These mutations are corrected by the excision repair mechanism of the DNA polymerase but sometimes they might be left out. In one of such cases, point insertions were...
  43. C

    Finding a point on a surface which is closest to given point

    Homework Statement Find the point on the surface z2 = xy + y + 3 which is closest to the point (1,2,0)Homework EquationsThe Attempt at a Solution Can someone check my work?
  44. D

    Point between Sun and Earth where gravity is zero?

    Find the point between the sun and the Earth where the gravitational force on an object is equal to zero I know the mass of the sun is 1.989 x 10^30 kg G = 6.67 x 10^-11 The distance between the two is 1.49604618 x 10^11 The mass of the Earth is 5.962 * 10^24 I have the equation F =...
  45. astrololo

    Calculate Apparent Weight at Point S

    Homework Statement When the train has passed at the point C, the radii of curvature is 20 m and the apparent weight is 2 2 times bigger than the real weight. At the moment when the picture was taken, the train was at the point s, located 8 m higher than the hollow C. At s, the radii of...
  46. M

    Help with a three point bending test

    Hello everyone, I am trying to evaluate the spring constant of a coaxial polymer cylindrical fiber. This fiber has a stiff core and a more soft sheath. I know the geometry of the system and I know the Young's moduli of both components. I can find separate models for the core or for the sheath...
  47. O

    Can two perfect point monochromatic sources be incoherent?

    I know none of the source can perfectly be monochromatic. All that we can talk about is the degree of coherence. What I wanted to know is that suppose magically some how I get two independent perfect point sources of monochromatic light, then will then two independent sources be act as...
  48. C

    Directional derivative at a point

    Homework Statement Homework EquationsThe Attempt at a Solution part a) finding partial derivatives: and plugging in (2,0,1) into each, I get the gradient which is <0,-2,0> to find the directional derivative, it is the dot product of the gradient and unit vector of (3,1,1): part b)...
  49. C

    Eq. of tangent plane at a point.

    Homework Statement Homework EquationsThe Attempt at a Solution what is the difference between the form z - zo = fx(x-xo) + fy(y-yo) and: Fx(xo,yo,zo) + Fy(xo,yo,zo) + Fz(xo,yo,zo)=0 ____________________________________________________________________________using the first eq : while...
  50. S

    Need Help with Solving Point Kinetic Equation for One group

    Does anybody can help solve point kinetic equation for one group of delayed neutrons in steps. I am looking forward to solve it by analytical methods. dn(t)/dt=ρ-β/l n(t)+ λC(t) dC(t)/dt= βi* n(t)/l- λC I would really appreciate your help as i am have to submit to clear this paper next week
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