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    A Working mechanism of NEFFUL clothing

    Recently I heard that NEFFUL clothes, when rubbed with our skin, could release anions (refer to attached image for more details). I do not doubt the generation of anion, due to Triboelectric effect. But could anyone advise, where does the "cations" that were produced during the ionization go?
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    Internal resistance of cells in parallel

    I know, as a matter of fact, that the equivalent resistance of three identical cells in parallel is equal to the internal resistance devided by 3. When we are concerning simply 3 equal resistors in parallel, I know that the outcome resistance is what. But when it comes to three cells with...
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    Can a solution contain only cations?

    For example, can Cu2+ be the only ionic species present in an aqeuous solution, without anions such as nitrate. (Hydroxide ions ignored)
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    Interference-thin glass

    As shown in the diagram , why only ray 2 and 5 are considered? When ray 4 strikes the top interface from underneath, some is reflected. Why this ray is not considered?
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    Oblique impact on ground of a ping ping ball

    When a ping pong ball strikes the ground obliquely without spinning, the angle of incidence is not equal to that of reflection, am I correct? Here is my thoughts: Assume the ground is smooth and negligible air resistance. When the ball touches the ground, it starts to deform, delivering its...
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    Acid-base equilibria

    You mean there is either equilibrium in a solution but not both?
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    Acid-base equilibria

    While I am studying my Chemistry lecture notes, I find the following notes with which I am rather confused: For a particular acid and its conjugate base HA + H2O = H3O+ + A- Ka= [A-][H3O+] / [HA] A- + H2O = HA + OH- Kb=[HA][OH-]/[A-] KaKb = Kw pKw= pKa + pKb = 14 (at 298K) I am...
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    Energy of elastic matters

    I am puzzled with the energy conversion (actually I think I am easily get stuck with PE, KE and work done) when an elastic matter is being stretched or relaxed. First of all, regarding the elastic hysteresis of a rubber, in the Force-extension graph, the area when the rubber is loaded...
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    Real gas PV curve

    Isn't the volume under consideration the gas volume? When the gas is liquified, there should be no volume...
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    Real gas PV curve [Broken] After the gas has been liquified, the gas volume should have disappeared. Why the liquid part of the curve still possess volume?
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    Mass Spring System

    The system concerning elastic pe is the mass spring and that concerning gravitational pe is mass earth system. Can they be added?
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    Mass Spring System

    In a SHM motion, the PE and KE of the system is of a complement relationship. However, in a vertical mass spring system, there seem to be two kinds of PE, elastic PE in the mass spring system as well as the gravitational PE in the earth mass system. So, what should be the PE of the SHM, and what...
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    Problems of Gravitation

    1) Two planets X and Y (sphere) both have 1 satelite revolving at low altitude about them. If the theri periods of rotation are found to be the same, which of the followings properties regarding X and Y is most likely to the the same? A) Mass B) Average density C) Acceleration due to...
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    Gravitational PE problem

    For A and B, I am not sure which is correct. Both seem to be reasonable. For D, I also don't know whether momentum can be "destroyed", but I think it is not the answer. As it seems to be quite irrelevant with the question. The trolley stopped because all the KE is converted to elastic PE which...
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    Gravitational PE problem

    Thanks. Besides, while I am drilling for my exam, I find I don't know how to think of this conceptual past paper question: A trolley travels with uniform velocity to the right on a horizontal ground and collides with a light helical spring attached to a wall fixed to the ground (earth). At...
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    Gravitational PE problem

    4/5 of a string of length L is placed on a smooth table while 1/5 of it hangs freely over the edge of the table, why the minimum PE gained by the string due to a force pulling it so that the whole string is placed on the table is (1/5 m) x g x (1/10 L) (This is the answer, but I don't know...
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    Problem about limits

    Yes, but I m not sure about the limit..I think it should be 1..
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    Problem about limits

    Given a function f(x) = lim n->infintiy [x]^n / (x^n +1) , where [x] is a greatest integer function. What is the limit value of lim x->1+ f(x) ? Is the limit found above the same with lim n->infinity (lim x->1+ [x]^n / (x^n +1) ) ? I am rather confused with the above two cases. I...
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    Rubber band

    So what is the true rational behind? And does it have something to do with elastic hysteresis?
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    Rubber band

    Why a rubber band gets warmer when repeatedly stretched and relaxes? Where does the gained ME comes from? Besides, does rubber band obeys Hooke's Law?
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    Definition of ideal gas

    Why it is not necessary for an ideal gas to obey Charles's law, but Boyle's only?
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    Why do the PE of atoms decrease when they form bonds

    In fact, why do the PE of atoms decrease when they form bonds, in terms of molecular interpretation, i.e. what actually happened in the atoms making they have lower energies?
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    About vector/complex number

    Why when we consider the inclined angle between two vectors , we must consider the angle anti-clockwisely? What is the reason behind?
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    Why when a chemical species is stablized by resonance, its energy

    Why when a chemical species is stablized by resonance, its energy level is lower? As I know, resonance is only a kind of electrons delocalization within the species. There is no interaction between that species and the environment.
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    Hybridization problem about guanidine.

    Structure of guanidine is as follows: The central carbon atom is obviously of sp2 hybridization and there is 1 unhybridized p orbital remaining. I suppose that the N atom doubly-bonded to C is of sp hybridization and the other 2 N atoms are of sp2 hybridization. Am I right?
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    About complex number

    The question is to express (1- i tanx) / (1+ i tanx) in polar form. First, multiple the whole fraction by cosx. It becomes (cosx - i sin x) / (cosx + i sin x). We can find the modulus and argument easily by using the fact that "if z1=r cis a, z2=r cis b , then z1 / z2 = r1/r2 [cos(a-b) + i sin...
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    About variation

    Given F is directly proportional to the product of m1 and m2. F is also inversely proportional to the r^2. F, m1, m2 and r are real numbers. Why we can link the above two variations together and say that F=km1m2/r^2, where k is the proportionality constant? Aren't the the variations...
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    How to prove such property?

    If pq=ab where p, b are relatively prime, p must be a factor of a and b must be a factor of q.
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    Friction problem

    Homework Statement Sand is poured onto a converyor belt at a constant rate of 25kg/s. The belt keeps moving horizontally at a constant speed of 4m/s. Homework Equations What is the fricional force acting on the sand? The Attempt at a Solution According to the solution, the answer...