# Tag Info

34

Good question. Assume we have one cube of ice in a glass of water. The ice displaces some of that water, raising the height of the water by an amount we will call $h$. Archimedes' principle states that the weight of water displaced will equal the upward buoyancy force provided by that water. In this case, $$\text{Weight of water displaced} = ... 33 Play-Doh is mostly flour, salt and water, so it's basically just (unleavened) dough. There are a lot of extra components like colourings, fragrances, preservatives etc, but these are present at low levels and don't have a huge effect on the rheology. The trouble with saying it's basically just dough is that the rheology of dough is fearsomely complicated. ... 30 Here is an explanation that needs no explicit equations. Consider the following diagram, in which part1 and part2 represent the ice. The displaced water volume equals part2 volume and has as much mass as (part1+part2) Now look at what happens when both part1 and part2 melt: their mass does not change, it is (part1+part2) it becomes water. And we just ... 28 Plasma is described as the 4th state of matter, which is what you get if you give so much temperature that the molecules begin to break up and ionize into positively and negatively charged fragments. Another Claim on the title '4th State of matter' is a 'supercritical fluid'. Sometimes people draw phase diagrams with it to show this '4th state of matter'. ... 19 Fire is neither. Fire is a process involving both. Fire is the energetic combination of various substances with oxygen to release light and heat. In a gas fire, such as might be found on a stove or in a heater, a light hydrocarbon such propane is broken down into components of hydrogen and carbon which unite with oxygen from the atmosphere to form water ... 12 In simple terms, there isn't any space in the ice crystal lattice for the extra atoms and there is no way to plug either of the ions (or the whole salt molecule) into the growing pattern. So more and more water joins the frozen mass, leaving a more and more concentrated brine until essentially all the water is frozen and the salt remains behind. As ... 11 Yes, of course, the freezing point will decrease by the pressure developed, while part of the water freezes. But do not underestimate the pressures! In such an experiment easily some thousand bares may be developed. (Depends on the rigidity of the vessel and the volume of water) Here is a video showing how freezing water cracks a cast iron sphere. ... 11 Yes, a plasma contains positive ions and negative electrons, but the positive ions don't need to be atoms. Actually the negative charges don't even need to be electrons. For example, plasma etching of silcon is done using a sulphur hexafluoride plasma that consists of (mainly) SF_5^+ and F^- ions. I'm not sure that the word plasma has a precise ... 9 @MartinBeckett's already gave an excellent answer: Salt is excluded from ice because there is "...no way to plug the ions... into the growing [ice] pattern." This unusually long answer -- a mini-tutorial really -- is an expansion on his answer. I've added a long background section that uses informal, easily visualized analogies to define a number of related ... 8 Matter is made up from point like fundamental particles, like electrons and quarks, that have zero volume. This puts us in the interesting position where the true volume of all matter is zero, and the only reason that everything doesn't instantly collapse into a point of zero volume is that the pointlike fundamental particles maintain a finite distance from ... 8 Formally, the incompressibility of a fluid is defined by the compressibility,$$ \beta=\frac1\rho\,\frac{\partial\rho}{\partial p}  where $\rho$ is the mass density and $p$ the gas pressure. This means that, the compressibility is the measure of how much the density (volume) changes when a pressure is applied. For water at standard pressure, this works ...

8

I mean, they are heavier than air. No. Water is $H_2O$ which has a molecular weight of 18. Nitrogen is $N_2$ which has a molecular weight of 28. Oxygen is $O_2$ which has a molecular weight of 32. Argon is $Ar$ which has an atom weight of 40. So a water molecule has a mass that is less than that of all the significant components of air. But ...

7

It's not a disturbance, the liquid isn't supercooled in this case. It's right about at 0 degrees, though. It isn't the pressure drop directly, because you can give an upper-bound estimate to how much cooling the pressure drop directly does based on the observation that the pressure is not more than a few atmospheres. That means that space the gas in the ...

7

Steam is water in a gas phase, while mist, or fog, are small droplets of water in the condensed phase, but small enough to be kept in the air by thermal Brownian motion. There is a huge difference in their properties. steam at 1 atmospheric pressure is defined to be water at a temperature of 100 degrees celsius or more. It is an invisible gas, and contains ...

7

In the case of liquids and gases, at least, there's no fundamental difference. To see this, take a look at Wikipedia's phase diagram for water. Ignore the dotted lines for the moment, and note that the line between vapour (steam) and liquid stops at a certain point, called the critical point. What this means is that if you go through the following ...

7

I'm going to guess the toy you actually have in mind is the stuff sold in the US under the name Silly Putty . Play-Doh is used primarily as a "modeling clay" for sculpture - which means it needs to behave as a "plastic" - it's yield strength needs be low enough to enable it to be worked into a figure, but high enough that reasonable sized figures don't ...

7

The noise is either from the AC electricity, which would be a 60Hz buzzing, or from small bubbles forming on the heating element itself. When the electricity stops, both the buzzing and the bubble formation will stop as well. Bubbles create sound due to quickly expanding from a small nucleus. Here's a book I found with a section on noise from bubble ...

6

While the physical properties of a solid vs a liquid are obvious to any grade-schooler, the physics behind it are a little more complex. A substance is traditionally called a solid if it will not noticeably deform from a given starting shape in its steady state (in simple terms, it will not "flow" in the absence of any force other than gravity). A liquid, ...

6

Liquids are a state of matter in which the atoms or molecules are held together by chemical bonds (a difference from gases) but the bonds are weak enough for the shape to be variable (a difference from solids). That's why it is not possible to increase or decrease their volume much; the amount of energy from these chemical bonds would rapidly increase ...

6

I can address one class of non-Newtonian fluids consisting of solid particles dispersed in a liquid medium, such as the cornstarch and water mixture commonly called "oobleck." In more scientific language, I am talking about concentrated colloidal suspensions of particles. Here is an image of oobleck, taken from Dounas-Frazer et al 2012. These fluids tend ...

6

A quick comment on your terminology. The description "non-Newtonian" just means the stress/flow rate graph is not linear i.e. there isn't a single constant viscosity coefficient. The fluid you describe is what we colloid scientists call "dilatant", and it is certainly non-Newtonian. However there are lots of other non-Newtonian fluids such as tomato ketchup ...

6

I suggest that looking for an explanation for 'fire' may be the wrong approach. Science is a process where we try to explain what we perceive. In doing so, we may have to sacrifice (or at least temporarily suspend) a common perspective. My presumption is that you are probably mostly interested in the visual manifestation of fire - the dancing flames. ...

6

Good question! The defining difference is that in a gas the atoms are intact, and in fact are typically bonded into molecules, whereas in a plasma at least some of the electrons separate entirely from their atoms. In other words, particles of a plasma are charged, but particles of a gas are mostly uncharged. So technically, a plasma is not a gas and it ...

6

Plasmas are a common part of the world we live in. The definition of plasma allows them to exist within an environment consisting mostly of bound atoms. A variety of human technology creates plasmas. The type I hear plasma researchers reference most is a simple RF Plasma. This is perhaps the most direct way to use electricity to shake off the electrons ...

6

In what ways can energy transform into matter and vice versa? Energy and matter are connected according to special relativity and this has been experimentally demonstrated . It is the famous formula: $E=mc^2$ , where $m$ is the relativistic mass and $c$ the velocity of light. or $E^2=m_0^2c^4 +p^2c^2$ , for a particle with rest mass $m_0$ moving ...

5

The point of the fuzzball conjecture is that spacetime is geometrically altered at the black hole horizon. Rather than having an interior, the extra dimensions pinch off at the horizon and encode the complicated data from incoming particles in complicated geometry. This resolves 2 issues There's no singularity because the black hole effectively doesn't ...

5

Topological order can not be described in Ginzburg-Landau symmetry breaking paradigm. It is actually fair to say that topological order are more or less the properties of (gapped) quantum phases that can not be captured by GL. One way to define it is to use the notion of adiabatic continuity: if two gapped phases of matter can be connected by adiabatically ...

5

Related note: Fission isn't exactly turning matter into energy. It just releases the binding energy of the nucleus. This binding energy is part of the measured mass pf the nucleus, but if you want to separate "matter" and "energy" (not really possible), then it counts as energy. $\newcommand{\a}[3]{\mathrm{^{#1}_{#2}#3}}$ ...

5

See Wikipedia for a list of available plasmas over there..! Or have a look below for the chart which shows variation of temperature and electron density in different plasmas..! A quick Googling would've provided the answer. Common examples include Lightning..! The Sun (from Core to Corona) Fluorescent Lights and Neon Signs Nebulae (Luminous Clouds ...

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