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. M

    MHB Point on Graph of Equation....2

    Determine if the given point lies on the graph of the equation. (a - 1, a + 1); y = x + 2 Let x = a - 1 Let y = a + 1 y = x + 2 a + 1 = a - 1 + 2 a + 1 = a + 1 Yes, the given point lies on the graph of y = x + 2. Correct?
  2. M

    MHB Point on Graph of Equation....1

    Determine if the given point lies on the graph of the equation. (a, 4a); y = 4x Solution: Let y = 4a Let x = a y = 4x 4a = 4a Yes, the point (a, 4a) lies on the graph of y = 4x. Correct?
  3. H

    A Understanding the Relativistic Action for a Point Particle

    The action for a relativistic point particle is proportional to the infinitesimal invariant length ds. Is there some more intuitive explanation for this? The action is defined by taking the time intergal over the difference between the kinetic energy and the potential energy. So how does this...
  4. Chatterton

    Figuring out which stars an exoplanet's poles point to

    I know Earth's north pole points to Polaris and during the 26,000-year precession cycle, it will also point to Demeb, Vega, and Alpha Draconis. But... Is there a reference that'll help me figure out what Proxima Centauri b's most likely pole star candidates would be? I know, so many variables...
  5. quantumfunction

    B Why is every event in spacetime limited to our present point

    I never got an answer to my original question Why can't an event where light from that event hasn't reached our present point in space and time, reach a past point in space and time in 4D space...
  6. Bunny-chan

    Distance between point coordinates in a straight line

    Homework Statement Let A = (1,2,5) and B = (0,1,0). Determine a point P of the line AB such that ||\vec{PB}|| = 3||\vec{PA}||. Homework EquationsThe Attempt at a Solution Initially, writing the line in parametric form\vec{AB} = B - A = (0-1,1-2,0-5) = (-1,-1,-5)\\ \\ \Rightarrow \vec{v} =...
  7. J

    Electromagnetism - The distance from point a to point b

    Homework Statement So I want to know the distance to 2. The proton is at v=0 at the 1. We know that: q=1.602*10^-19 point 1 L=1mm v=1.1*10^6 at point 2 F=1.44*10^-12 at point 1 Homework Equations [/B] E=(1/4πε)*(q/r2) ΔV=∫E*dr=(1/4πε)*q∫(1/r2)=(1/4πε)*q*(1/r2-1/r1) ΔU=ΔK=mv2/2...
  8. A

    Higher Potential with reference point

    Reference point was chosen to be at Va. I'm trying to understand the logic behind it. It is clear that Vc = - Vs because if Vc was the reference point at Va the voltage potential between Va and the reference point Vc is Vs. Therefore, Va = Vs, Va - Vc = Vs if Vc is reference. However, when Vc...
  9. RamosPinto

    I Two point boundary problem - Shooting method

    I'm currently trying to solve the following two-point boundary problem by means of the shooting method: To clarify, I'm investigating the optimal route of aerial/marine vehicles from one point to another point, considering a flow field. * The starting and ending locations are set as x0, y0...
  10. N

    What direction does a compass point to in a magnetic field?

    Hello Today we did a lab and one of the activities was having a compass underneath a wire while the current was off. The wire was straight so that it was directly aligned to be with the needle of the compass. One the current was flowing, the compass arranged itself in that it was not exactly 90...
  11. Mr Real

    Why does adding solute particles decrease the freezing point?

    When solute particles are added to a solvent boiling point increases, I am quite clear with its explanation (in terms of vapour pressure) but when it comes to freezing point, why does it decrease? What does it have to do with vapour pressure? My textbook says it's because liquid and solid state...
  12. B

    Electric field of a point charge above a plane conductor

    Some things I did not get are, 1): In the third para, it is said that potential approaches ##\infty## at ##Q##, why ? 2): In last para, The z component of field by ##Q## is said to be ##-Qh/(r^2 + h^2)^{3/2}##, Why ? should not it be ##+Q## not ##-Q## has the charge itself is positive. 3): I...
  13. hsdrop

    B Does Light Speed Affect Mass of Surrounding Objects?

    I know that when anything starts moving close to the speed of C (light speed) it ganes mass from an outside perspective. Does the same apply in the reverse? From the perspective of the thing that moving close to C does everything around it lose mass??
  14. maistral

    A 2D Cartesian Laplace equation with a single point diffusion

    Hi. I have this problem in trying to solve this PDE analytically. The PDE is represented by this diagram: Basically this is solving the Laplace equation with those insulated boundaries except it has that point diffusing its value across the plane. I know how to solve the Laplace equation...
  15. L

    Solving for Minimum point Excel

    Homework Statement [/B] Hello, I trying to solve for the minimum value that the x and y components reach in plot (A). I know that you can perform this using IgorPro but I would like to know how to solve for it using Excel. The plot was constructed using the following data points: 110...
  16. S

    I Possible to estimate the location of a measurement point?

    Hi guys, I am just wondering if it is possible to calculate/estimate the location of measurement point on a rigid body? For example, let's say we have a rigid body that is in motion. We attach a sensor, say an accelerometer on the surface of the rigid body. Now can we estimate the location of...
  17. S

    I What is the point of a spacer in neutron activation?

    I'm just reading over some experimental notes for neutron activation analysis and I see the mention of a spacer being placed between the irradiated sample and the detector face. What does a spacer actually do? I did a quick google but couldn't really find anything.
  18. yecko

    Slope of a curve and at a point

    Homework Statement http://i.imgur.com/In40pGm.png Answer: C Homework Equations f'(x)=slope=(y1-y2)/(x1-x2) The Attempt at a Solution I can't even list a valid formula for that... like I tried to integrate f'(x), but f(x) is with y so I don't think I am thinking in the right direction. What...
  19. B

    Torque around a point from lever linkage

    Hi all. Brushing up on some of my force and torque stuff so I can do some modelling in software. Homework Statement I have a system as shown in the picture. A force F acts at point A, which is the end point of the lever AB. Connected to the lever is a link BC, and connected to BC at point C is...
  20. DaniV

    The charge of point inside a conductive ring

    there is power source grounded, with electric power of 20v the negative side of the wire we connect to a pointy metalic button and the positive side of the wire we connect to a metalic conductive ring with radius of 7.5 cm as...
  21. B

    Logical Point in Topological Problem

    Homework Statement Consider ##\mathbb{R}^\omega## in the uniform topology. Show that ##x## and ##y## lie in the same component if and only if ##x-y = (x_1-y_1,x_2-y_2,...)## is a bounded sequence. Homework Equations The uniform topology is induced by the metric ##p(x,y) := \sup_{i \in...
  22. I

    Calculating the moment of inertia of a rod as a point mass

    The moment of inertia of a rod with consistent density rotating about its end is M(L^2)/3. However, if you treat the rod as a point mass and try to calculate this using mr^2, you get M(L/2)^2=M(L^2)/4. Why doesn't this work?
  23. O

    What's the Velocity at the Highest Point of a Swing?

    So currently I'm stuck in a topic which I don't understand because either my teacher is doing wrong or I'm just blind to see my mistake I want to know the velocity of a object at the highest point in a swing (looping is the German word, I'm not sure if it's the same in English) (I don't know...
  24. MiketheMuman

    Have CFM at one point, need to find it at another point

    I am designing a dust collection system for a powder mixing project. My current setup is basically a tent (roughly 6ft X 4ft X 7ft) with a dust collector tube hanging from the ceiling (or coming from the floor). I know the CFM, air properties, and pipe area at the end of the dust collector...
  25. physicsdude101

    Inertia tensor for point masses

    Homework Statement Three equal point masses, mass M, are located at (a,0,0), (0, a, 2a) and (0, 2a, a). Find the centre of mass for this system. Use symmetry to determine the principle axes of the system and hence find the inertia tensor through the centre of mass. (based on Hand and Finch...
  26. LouysHong

    I Launching a particle at the highest point inside a sphere

    If a smooth sphere with radius a is fixed on a plane, and a particle is projected horizontally at the highest point outside/on of the sphere with speed (4ag/5)^0.5, I know that the particle will lose contact with the sphere when it makes an angle of theta with the upward vertical, where theta is...
  27. Vavi Ask

    Measuring Molecular Mass with Freezing Point Depression

    Homework Statement 6g of non-volatile solute dissolved in 500g of water freezes at 272.64K. What is the molar mass of the solute? Data given- Tsolution = 272.64K Kf = 1.8 wsolute = 6g wsolvent = 500g 2. Homework Equations ∆Tf = T0 -Tsolution ∆Tf = Kf × molality (m) The Attempt at a Solution...
  28. A

    Find the equation of the plane given point and line (3D)

    ∴1. Homework Statement Find an equation for the plane that contains the point (1,-1,2) and the line x=t, y=t+1, z=-3+2t? 2. Homework Equations The Attempt at a Solution I don't know what I am doing wrong but everytime I try to do these plane questions my amswer is always the opposite sign of...
  29. dbuhtoia

    Electric field with three charges and a point

    refer only to the image above, not the question 4.) Two point charges, Q1 and Q2, are placed 0.30 m apart on the x–axis (shown in the figure above) Charge Q1 has a value of –2.50 x 10–6C. The net electric field at point P is zero. a. What is the sign of charge Q2? ____ Positive ____...
  30. RabbitWho

    Finding the force of repulsion between two point charges

    Hello! So this is going into physics because it is a physics problem, but it is maths that is the real problem. So if you came here to help someone with physics and not maths I'm sorry. 1. Homework Statement Find the force of repulsion between two point charges of +1C and +3C if they are...
  31. D

    I I need to find out the forces acting on an anchor point

    Hello all. i am after some help and hopefully you are the right people for this! i have a problem will a kitchen wall cabinet. i can only get fixings which rate at 40kg, but i work out my cabinet fully loaded (including self weight) could be 95kg. i have attached a drawing which hopefully...
  32. CMJ96

    What happens at the lambda point of superfluid Helium?

    Homework Statement 2. Homework Equations are given in the above picture 3. The attempt at the solution In part a) I simply rearranged the other expressions given and subbed them into the relationship for relative velocity and came out with Vns= Qdot/ρsT(1- ρn/ρs).Then in part b) I started by...
  33. Z

    Java Draw circles at end Point of Line with End Points as Centre

    Hi, I am trying to draw circles at the end points of a line but circle centre is not exactly on the end point of the line. Can somebody please guide me. import java.applet.Applet; import java.awt.*; import javax.swing.*; public class JCircle extends Applet{ int x1=30; int y1=30...
  34. Schaus

    Find Point c that satisfies the Mean Value Theorem

    Homework Statement Find the point "c" that satisfies the Mean Value Theorem For Derivatives for the function ## f(x) = \frac {x-1} {x+1}## on the interval [4,5]. Answer - c = 4.48 Homework Equations ##x = \frac {-b \pm \sqrt{b^2 -4ac}} {2a}## ##f'(c) = \frac { f(b) - f(a)} {b-a}## The Attempt...
  35. J

    Deriving expression for potential of a point charge

    Homework Statement I am trying to derive an expression for the potential of a positive point charge by bringing in another positive test charge in from infinity to a point at a distance R from the point charge. Homework Equations $$V_f - V_i = - \int \vec E \cdot d \vec r \, dr$$ The Attempt...
  36. T

    Collision of point mass and sphere in particular fashion

    1. Homework Statement a point mass is projected at an angle of 60° from the horizontal. it collides with the sphere at a maximum height of trajectory with a sphere of radius of 72.5cm such that it is projected off the sphere once again at an angle of 60° from the horizontal.The sphere, due to...
  37. R

    Thermodynamics Gas Mixture - Dew Point Temperature

    Homework Statement Only Number 1, not number 2 Homework Equations Dew Point Temperature T = Saturated Temperated at Vapor Pressure Partial Pressure = (mole fraction) x (Mixture Pressure) The Attempt at a Solution The dew point temperature is only dependent on the pressure of the water...
  38. R

    Gas Mixture - Dew Point Temperature

    Homework Statement Only Number 1, not number 2 Homework Equations Dew Point Temperature T = Saturated Temperated at Vapor Pressure Partial Pressure = (mole fraction) x (Mixture Pressure) The Attempt at a Solution The dew point temperature is only dependent on the pressure of the water...
  39. K

    Electric field created by point charges and conducting plane

    I came upon this: http://physics.stackexchange.com/questions/174514/will-the-electrostatic-force-between-two-charges-change-if-we-place-a-metal-plat/323006#323006 question on Physics Stackexchange which I found very interesting. The configuration is basically two positive point charges q and...
  40. V

    Point of Maximal Tension for Vertical Circular Motion

    Homework Statement A heavy mass m is attached to thin wire and whirled in a vertical circle. Then the wire is most likely to break A only when mass is at the lowest B somewhere between lowest point and horizontal point C only when mass is horizontal D only when mass is at highest point...
  41. S

    Find the magnetic field at the point

    Homework Statement A long, straight wire lies along the z−axis and carries a 4.20 −A current in the +z−direction. Find the magnetic field (magnitude and direction) produced at the following points by a 0.400 −mm segment of the wire centered at the origin. Homework Equations ## \vec B ## = 2...
  42. X

    B Why can we choose any arbitrary point to calculate the moment?

    Can someone explain, what means that we can choose any arbitrary point to calculate moment and result will always be identical? If I choose point 1 ...20kg x 1m = 20kg x 3m...seesaw right side will fall down If I choose point 2...20kg x 2m = 20kg x 2m...seesaw stay horizontal So this two...
  43. R

    What causes a point charge to move in an electric field?

    Homework Statement : STATEMENT:[/B]A point charge at rest is released in an electric field. It will move along the electric field line...(1) REASON: The force on a point charge is along the field line...(2) State whether: A) 2 is the correct reason for(1) B) Both (1) and (2) are correct but 2 is...
  44. O

    Torque Equation about a point other than point of rotation

    Hello all, These days I am studying rotation and rolling of bodies. We know a body can be made to rotate about any point. Let's assume that an external force is acting on the rotating body fixed about the point of rotation, and this force made the body rotates faster that is its torque produces...
  45. A

    Capacitance between point charge and finite plate

    I need help trying to set up this problem. I want to find the capacitance between a point charge and a finite plate (or disk) as the point moves from above the center of the plate to some distance off the plate. I have been able to simulate this problem using FEM, however, there should be a...
  46. zwierz

    A Particle in the point gravity and the Lorentz field

    Hi I will write physics terms but actually this is a math problem. Consider a particle which moves in accordance with the following equation $$m\boldsymbol{\ddot r}=\boldsymbol B\times\dot{\boldsymbol r}-\frac{\gamma}{r^3}\boldsymbol r,\quad r=|\boldsymbol r|\qquad (*)$$ and...
  47. danielhep

    MasteringPhysics: Find the angle between the point charges.

    Homework Statement Two m = 4.0 g point charges on 1.0-m-long threads repel each other after being charged to q = 80 nC , as shown in the figure. What is the angle θ? You can assume that θ is a small angle. Homework Equations Fe=kq2/r2 F=ma Fg=mg The Attempt at a Solution Equation 1:[/B] r =...
  48. Blank_Stare

    At what point does the atmosphere become space?

    A few years ago, a Australian guy jumped from a platform that was attached to a weather balloon, from roughly 24 miles or so in the atmosphere. News articles claimed he jumped "From the edge of space". https://en.wikipedia.org/wiki/Felix_Baumgartner But did he?, I mean clearly 24 miles is an...
  49. 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...
  50. 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...
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