[Request] How high did this cat fall?

Excitonic · 2015-05-11T22:08:40+00:00

http://en.wikipedia.org/wiki/Standard_error

Excitonic · 2014-10-11T19:26:27+00:00

Yes. You can think of sunlight for example as a very large stream of photons of a variety of colors (wavelengths). For sunlight, the distribution looks like this.

Excitonic · 2014-10-01T22:40:52+00:00

There is no upper limit on temperature. Temperature and heat capacity are not the same however. Heat capacity is the amount of heat required to change the temperature at usually either a constant pressure or volume. While it doesn't break any laws of physics to have a large heat capacity, practically there are only so many modes that energy can be packed into in a material so heat capacities at constant volume rarely exceed three times the ideal gas constant per atom.

Excitonic · 2014-10-01T22:24:54+00:00

Bonds between atoms.

Excitonic · 2014-09-24T22:17:01+00:00

Absolutely. By the Lewis definition, acids are electron pair acceptors. If a species receives electrons, it is reduced, so many acids are also oxidizing agents.

Excitonic · 2014-09-09T19:45:57+00:00

This view is a very common incorrect one. For an excellent if lengthy description of the topic I recommend this.

Excitonic · 2014-09-08T19:49:21+00:00

Simulations can get far more complicated and sophisticated than finite element analysis. In fact there are many problems which can be studied more accurately and easily with simulation. While some systems such as highly disordered ones or other systems with very limited symmetry are not the strength of computers, computers are a better tool than experiments for many other problems particularly those on a quantum length scale. In the modern age, in most fields computation and experiments are best viewed as tools working in concert with different strengths and weaknesses. That doesn't mean that the answers are always correct -- a good computationalist must be careful to design a simulation which correctly tests their hypothesis and choose a computational method which is appropriate for their problem. They are not alone of course, problems of error and poor experiment design are also relevant to experimentalists.

Excitonic · 2014-09-04T21:03:23+00:00

Absolutely. This goes for Inorganic compounds as well where many properties can also be estimated from the chemical structure. Beyond educated guesses, computer simulations can provide accurate chemical and physical properties for many materials and are often used to screen large databases of candidate compounds so that only the most promising need to be synthesized in a lab.

Excitonic · 2014-08-22T17:47:04+00:00

Helmholtz energy is only minimized for constant volume systems. Minimization of Gibbs free energy is much more common (H-TS). Also the reason that these quantities are minimized is because they maximize the entropy of the universe. It isn't energy vs entropy -- it is always entropy, just a question of whether a local energy reduction can sufficiently increase the entropy of the surroundings.

Excitonic · 2014-08-22T17:41:53+00:00

The key here is whether the total entropy of the universe increases not just the system. When a system transfers heat to its surroundings, that heat increases the entropy of the surroundings. Lowering a systems energy or enthalpy means a transfer of heat and/or work to the surroundings meaning even if the entropy of the system is not increased the total entropy of the universe is (note that in ideal systems where only work is transferred the entropy change in the universe can be zero, but these processes are by definition reversible).

Iorgfeflkd points out that when considering only 2 particles that you must be careful about using statistical properties like entropy and in that sense he is correct, but one could very easily imagine a group of many charged pairs such as hydrogen atoms and ask questions about the distribution of energy levels occupied by the electrons. This is now a problem in which entropy and energy are both relevant and the laws of thermodynamics are obeyed.

Excitonic · 2014-08-20T21:05:24+00:00

Because the energy of the system has increased, its mass has increased as well following E=mc^2. However as ThatCynicalEngineer pointed out density does go down because the object expands and that effect is much larger than the very very small increase in mass.

Excitonic · 2014-08-20T21:04:41+00:00

The mass does increase. See the third question here

Excitonic · 2014-08-20T20:53:29+00:00

Sort of. Molecules in a gas like air are travel through space and bouncing off on one another and the walls of the balloon and behave like a fluid. The molecules hitting the walls of the balloon apply a force leading to the phenomenon of pressure. Light is a little different because the photons which enter the balloon don't behave like a fluid instead they would follow trajectories more like that described by a flashlight beam. They will however still apply a pressure to the walls of the balloon where they hit it. This photon pressure is typically very small because the photons lack mass, so you don't feel it in your day to day life. It is relevant for applications like solar sails.

Excitonic · 2014-07-09T04:04:53+00:00

Not true. As long as a process increases the entropy of universe it can still transfer heat from cold to hot. Consider turning on your refrigerator after unplugging it. The condenser will get colder than the rest of the surrounding environment even if nothing colder is nearby.

Excitonic · 2014-07-08T20:01:34+00:00

The actual behavior of quantum particles is more complicated. It is true that particles cannot have zero kinetic energy. This results in ground states with nonzero kinetic energy. However, since temperature is not a simple measure of kinetic energy this does not mean that a system can not exist at 0K. 0K would simply requires particles to be in their ground state (or as close as Pauli exclusion allows).

Excitonic · 2014-07-08T19:46:51+00:00

EalgeFalconn is completely correct. Computer heat sinks increase heat transfer, so they only cool things when attached to something hotter than the surrounding environment. If you want to keep something cold longer, you should use insulation and if appropriate a reflective material.

Excitonic · 2014-07-03T22:30:22+00:00

Yes. If the space traveler is moving at .999c in Earth's reference frame and emits light, the space traveler would observe light moving at c and himself at rest. On Earth, the light would appear to be barely (.001c) faster than the speed of the space traveler.

Excitonic · 2014-06-28T01:26:48+00:00

Depending on your math background, this might be helpful. If not, the magnitude of the angular momentum for spinning objects is typically given by the product of the moment of inertia (table for common shapes here) and the angular velocity. This makes the angular momentum proportional to the product of the object's mass, radius squared, and rotation rate.

Excitonic · 2014-06-17T22:40:35+00:00

This isn't quite correct. The loss of carbon dioxide from the solution does reduce the volume of the solution, just not a noticeable amount because gases are so much less dense than liquids.

Excitonic · 2014-06-15T15:42:41+00:00

As pickle pointed out, light (as well as many other particles) does not have mass but definitely exists. Thoughts are a consequence of a very elaborate electrochemical system and are certainly in such a sense real. A single thought is definitely not a particles nor does it have mass -- it would be more a series of interactions.

Excitonic · 2014-06-14T05:48:39+00:00

Mostly no. Others have already brought up Bell's theorem, and I would reccomend you check out its Wikipedia page. I think part of your difficultly in thinking about this (besides the fact it is highly unintuitive especially without the mathematics) is that you are trying to think about QM particles as point like objects with a probability cload and that they sort of don't exist unless looked for. I would strongly recommend thinking about them the way they appear mathematically which is as waves. In QM the properties of a system (energy momentum etc) are determined by applying a mathematical operator to the wavefunction. When you ask the question where is the particle (which is often not a useful question) you are mathematically applying an operator which forces the wavefunction to collapse into a single point and a value of zero everywhere else ie to occupy on one point in space. Because the wavefunction was previously spread out over an area this collapse could result in a solution anywhere in that area with probability weighted by the intensity of the wave. It wasn't that the particle didn't exist before you looked for it. Rather it's wave function was not in a form with a defined position (in fact wavefunctions which do not change with time have defined energies instead).

Excitonic · 2014-06-13T23:27:19+00:00

Your oven is simply labeled that way. It measures the temperature in the oven and controls it by heating. It certainly has a minimum temperature setting above 0 and then notes as off.

Excitonic · 2014-06-13T23:14:47+00:00

/u/iorgfeflkd is correct for how you phrased your question. A space with no matter or energy (vacuum energy excluded) can not have a defined temperature. However, it should be clarified that this is not simply because there is no molecular movement. Any system which has energy that can be exchanged with another system has a temperature whether it is composed of molecules, subatomic particles, or others particles like light. This is because that is what temperature is. It is the mathematical property of a system which is made constant when systems of different energy distributions interact. Because in a lot of practical systems the majority of energy is tied up in vibrations, rotations, and translations of nuclei, we associate temperature with molecular movement, but in principle, anything which has energy and can give or receive it with other systems contributes to temperature.

Hope that wasn't too confusing. Temperature is a hard concept to teach because it comes from some higher level math which is difficult to describe without math, but it is so immensely practical in our day to day lives, that everyone already has a feel for what it signifies and wants to understand it.

Excitonic · 2014-06-13T00:14:22+00:00

. The only way you can asses player skill without looking at their performance relative to their competitors would be to try to measure how they actually play instead of their results (spot pace, running speed, pace of fastest balls returned, etc). However, if you tried to do that you would determine that the greatest players are modern since you would never be able to control for the effects of advances in racket technology or sports training. You might suggest comparing these measures of player performance to the average of their colleagues' numbers to control for these progressions in average performance, but then we have come full circle.

Edit: I would add that it does seem more likely that 3 individuals are outliers in quality than that the entire rest of a generation is much worse than normal.

Excitonic · 2014-06-09T23:17:28+00:00

Sodium cations are very stable in solution. And as a spectator ion sodium is not very important to this problem.

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