Liquid Definition and 33 Discussions

A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, and plasma), and is the only state with a definite volume but no fixed shape. A liquid is made up of tiny vibrating particles of matter, such as atoms, held together by intermolecular bonds. Like a gas, a liquid is able to flow and take the shape of a container. Most liquids resist compression, although others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly constant density. A distinctive property of the liquid state is surface tension, leading to wetting phenomena. Water is, by far, the most common liquid on Earth.
The density of a liquid is usually close to that of a solid, and much higher than in a gas. Therefore, liquid and solid are both termed condensed matter. On the other hand, as liquids and gases share the ability to flow, they are both called fluids. Although liquid water is abundant on Earth, this state of matter is actually the least common in the known universe, because liquids require a relatively narrow temperature/pressure range to exist. Most known matter in the universe is in gaseous form (with traces of detectable solid matter) as interstellar clouds or in plasma from within stars.

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  1. sumatoken

    Study of harmonic motion of a liquid in a V shaped tube

    A V-shaped tube with a cross-section A contains a perfect liquid with mass density and length L plus and the angles between the horizontal plane and the tube arms as shown in the attached figure. We displace the liquid from its equilibrium position with a distance and without any initial...
  2. brotherbobby

    An exercise with Pascal's Law

    Answer : Using Pascal's law, this is my answer : ##\color{blue}{\boxed{\vec F_a = \vec F_c < \vec F_b}}##. Reasoning : Forces ##F_a## and ##F_c## are equal because the pressures required at the two cylinders for case (c) is the same as that required in (a). It doesn't matter how many of those...
  3. Vivek98phyboy

    Reason for Calculating Surface tension

    When calculating force due to surface tension across a hemispherical drop, we look at only the circumference and multiply it by the value of surface tension. When we know that it is the surface tension which is responsible for the curved surface of the liquid drop, why don't we calculate the...
  4. harsh22902

    Surface Tension and Capillary Rise

    According to this definition I am unable to understand why does surface tension acts tangentially to surface of contact of liquid and capillary tube. And is the force of surface tension balancing the adhesive forces which lead to capillary rise OR it is the reason behind the capillary rise?
  5. Michael_0039

    Undergraduate physics: Body flows inside liquid [ v(x)=? and V(lim)=? ]

    Homework Statement: Object inside liquid Homework Equations: T=k*v^2 F=m*a We hold an object with a mass (m) inside a liquid. On t=0 we free the object. Except the weight there is another one force, the friction of the liquid, witch is T=k*v^2 ( v=instant speed, and k=constant > 0). Also...
  6. QuarkDecay

    Flow (liquid or gas) across a rotating surface's face

    << Mentor Note -- Two threads on the same question merged into one thread >> How does the maximum Power equation change if there's an angle to the way the wind falls into the wind turbine's blades? Example, when it falls vertically to the blades, it's Pmax= 8/27Sρu13 But if there's for...
  7. G

    I Pascal's law (fluids): Derivable from fundamental laws?

    Hi. Pascal's law states that static pressure in a confined incompressible fluid without gravity is the same everywhere. Is this law derivable from more fundamental laws? Some thoughts: Is Pascal's law part of the definition of the liquid state? If the liquid operates between two hydraulic...
  8. Logic hunter

    B How does liquid starts moving when there is Pascal's law

    Consider a conventional U-tube with both the vertical tubes having the same uniform cross section area A and the horizontal tube of length L, connecting those tubes containing an ideal liquid. Now the free surfaces in both the vertical tubes will be at the same height and will have pressure...
  9. Logic hunter

    B Direction of buoyant force on sunken object?

    We say that buyont force act upwards (in usual cases) and that the normal force exerted by the base of a container (of liquid) on a object is less than its true weight, so a weghing machine will give smaller reading (in terms of value) than expected. But suppose a cube sinks in water. Now water...
  10. J

    Pressure and boiling

    Hi everyone, I have been mulling over the relationship between pressure and boiling for some time, and I am still slightly confused. I shall attempt to provide an overview of my current understanding in the hope that I can get some corrections/clarification on my current conceptual...
  11. A

    What do surface tension vectors mean in this quote?

    I was reading Fundamentals of Inket Printing and it said the following: "The surface tension in a liquid causes a force to act in the plane of the free surface perpendicularly to a free edge in that surface." Can someone explain to me what this means? What's the direction of the force? I have...
  12. L

    Why do bubbles of air in water move up?

    What I am confused about is why do bubbles of air in water move up. I understand why solids and liquids would move up in water if they are less dense. I get the idea that the deeper you go in water the more pressure there is because of the more water weighing down on the water and so there would...
  13. I

    The acceleration of a bubble in water

    Hi, I have a question about a rising bubble. I read that the initial acceleration of a bubble (with negligible mass) in water is 2g, where g is the gravitational acceleration. I understand that if a bubble rise then the water move around it, but I can't derive this equation. Could someone help...
  14. dromeascr

    Question about vapor pressure

    Hello everyone, before I start I just want to mention that I am not an expert in physics whatsoever, so please be as specific as you can get if you wish to provide an answer. (The question itself might be considered stupid to be honest) I read the definition of the boiling point recently and...
  15. EEristavi

    I Liquid boiling and Evaporation

    In the normal conditions (sea level) water evaporates at 100 C. In thermodynamics, we say: the amount of energy Q, can raise temperature of the liquid by the formula Q1=cm(t2-t1); when the liquid reaches the boiling point (100 C), we write Q2=Lm. Q2 is entirely spent on changing liquid state...
  16. K

    Thermal expansion of liquid into gas void

    I have a question about thermal expansion of liquid into a gas void. Imagine a closed upright cylinder filled mostly with water – say 99%, and the remaining 1% is gas. Now imagine that you heat the cylinder and its contents. The water will expand by ΔV owing to thermal expansion. The gas...
  17. M

    I Dissolved gas concentration in undersaturated liquid column

    Hi, In an enclosed system - of say Methane & water - in which the water column is sufficiently large to have significant pressure and some modest temperature difference due to gravity and geothermal effects, how would one calculate / predict the changing methane concentration (or partial...
  18. R

    B What is the concept of Physics of Cymatics (of a liquid)

    Hi, Could someone please help me about what is the physics concept behind Cymatics. Is there a formula which establishes the patterns form on a liquid when the frequency or amplitude are changed? Thanks.
  19. S

    Floating block with objects that are thrown in a liquid

    Homework Statement I'm confused about the following kind of situation. Consider a block of density ##\rho_b##, mass ##M_b## and section ##S_b## that floats on a liquid of density ##\rho_l##, in a tank of section ##\mathcal{S}##. On the block there are some objects (all equal), of density...
  20. salaheddine

    How can i calculate the time delay in arduino?

    hi every one , I'm a student in university , i have a projet it's about calculate speed of waves in liquid by to piezo electrique , one workd like emmeter and the other receppter , the distance betwin the two piezo is fixe , the probleme is i nedd to calculat the time betwin the moment who i...
  21. Mastico

    A paint for magician's trick?

    Greetings Forum Members, I am quite new to this & this is my first post. To tell you guys a little bit about me I am a magician that creates effects and I figured that when I am stuck I should go somewhere and ask people that are smarter than me :-). First Question: Is there any kind of...
  22. S

    Fluid Dynamics - Pressure at the end of a syringe

    Hello there Physics Forum! This is my first post here. This problem has been boggling me all day and I'm need of help in piecing together what I've come up with so far. I'm currently working on a personal project related to paint spraying. In this project I'm using a syringe & needle to feed...
  23. Stephanus

    Standard Enthelpy of water

    Dear PF Forum, As per wiki: Standard enthalpy of water: Gas: -241.818 kJ/mol Liquid: -285.8 kj/mol What does it means? That to produce H2O per mol at 1000C, it releases 241.818 kJ. That to produce H2O per mol in...
  24. Dlhill13

    Liquids and Electricity

    Hello everyone, I am currently working on a project to design a more efficient method of electricity production in the nuclear industry. I haven't been able to find anything online (and chemistry isn't exactly my strong suit most of the time), but I wanted to know if anyone knows of a liquid or...
  25. R

    What causes the liquid to rise in this picture?

    This is a diagram of a pitot-static tube. My question is however not related to its applications but rather, what causes the liquid to rise up the static tube? The static tube is at right angles to the fluid flow. I understand that this is a very basic question but I can't seem to get my head...
  26. A

    Interpreting Kinetic Temperature for Solids / Liquids

    Hi all, I'm brushing up on some thermodynamics, and having been reading up on the interpretation of temperature as derived from kinetic theory. I can follow the derivation for an ideal, monatomic gas which relates temperature to the average, translational kinetic energy of the molecules. Most...
  27. Tam Le

    Aqueous Solution

    What are we referring to when we denote, say, NaCl (aq)? Are we referring to the dissolved NaCl (Na+ and Cl-)? Are we speaking of the solution as a whole (the dissolved NaCl and water)? Also, how does the liquid state differ from an aqueous?
  28. Z

    Liquid Hydrogen Boil-off

    I've read a fews post about liquid hydrogen boil off, but could use a bit more clarification; insight on the following thought experiment would be really helpful: What happens if I take a 1 L steel vessel, put 1 L of liquid H2 into it, seal it off, and let it sit in a room at 25C? The density...
  29. AdityaDev

    Fluids and thermodynamics

    Homework Statement Homework Equations height of liquid above water level ##h=\frac{2T}{R\rho g}## for isothermal process :##PV##=constant And if ##P_0## is atm. pressure, and P is pressure just below the water level in capillary tube, then $$P=P_0-\frac{2T}{R}$$ The Attempt at a Solution...
  30. ryanuser

    Magnetic liquid

    Hey Is there any liquid available that is magnetic at room temprature? I know that liquid helium is magnetic but at very low tempratures not at room temperature. Thanks
  31. A

    Calculation of the force exerted by a liquid

    Question: The height of the given vessel is h,and the width of the given vessel is b (as given in the diagram). The density of the liquid is r.Find the force exerted by the liquid on the slant wall. Relevant formulae : P = F/A F = Vdg An attempt at the solution...
  32. R

    Ferromagnetic powder question!

    Hello! I am trying to understand a few properties of the ferromagnetic powder. I could not get the answers to these questions on the web, since any kind of phrasing i used, popped up search results that related to iron powder or ferromagnetic powder, which are manipulated and shape-shift...
  33. K

    Exam question that I have no idea how to solve (regarding forces and mass)

    1. The problem statement Peter threw 10 (same) coins into an empty container (a tube/drum), which was floating in A LIQUID. The diameter of the container was 2,257 cm, and so because the container is a tube the surface of the tube was equal to π times the diameter squared. He measured, after 4...