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Everything posted by jian

  1. are you sure you can explain everything?
  2. polymers are generally called soft materials. Liquid crystal ans biopolymers also are classified soft materials/matter. Their feature is that interaction forces between molecules are quite weak(around kT). They have strong response to the small stimulus. However, there properties are strongly dependent on temperature. Normally, there is a critical temperature at which they undergo soft hard transition. For polymer, that is the glass transition temperature. Magazine " Soft Matter" is the scientific publication concentrated on soft materials. You may check it out.
  3. If you use the concept of entropy, then all the statements are equivalent. There is a site explains the 2nd law quite well. http://www.panspermia.org/seconlaw.htm
  4. why not Hydrogen? It reacts with almost all the elements. Its isotopes have huge amount of atomic energy. It is our hope for the future.
  5. Then I have a question about the intermolecular force in PET. Is there any hydrogen bonding between the PET chains?
  6. Ether has very similar structure as alcohol. Why there is hydrogen bonding in alcohol but not in ether? Oxygen atoms have two lone pairs in both cases.
  7. fingerprint identification is one way. But it seems to be not practical to cause so much just for one brush.
  8. jian

    I'm bored...

    Bored by what? I am a bit bored by study.
  9. I have learnt a module about phase transformation. It states that melting occurs at the melting point because the liquid can always wet its solid,mathematically, it is [math]\gamma_{SV}>\gamma_{SL}+\gamma_{LV}[/math]. I am wondering does it mean that melting can occurs a bit lower than the melting temperature because the interfacial energy also perform as a kind of driving force. In addition, can anyone think a way that make melting starts from inside the solid not the surface?
  10. That is not log rule, is basic rule like a(b+c)=ab+ac. it is true.
  11. jian

    global warming

    It is possible but it is not that easy!
  12. Here, V must increase to keep P and n constant. n is the mole of the air inside the balloon, it cannot be changed as hot air doesn't leak out. With the constant n and larger V, its density is smaller, lighter. I doubt about this statement. What you talk about here is the molar mass, it is rather different with density. If we consider the moist as a mixture of water(liquid) and dry air, apparently, the density of moist air will be larger. I can also explain in your point, 1 mole of dry air occupies much larger volume than 1 mole of water. The differences in volume is much larger than the difference in mass when we consider the same quantity of dry air and water. Overall result is that density will be increased when water droplet is added.
  13. The air expands as heated becauses the average separation of the gas molecules get larger at higher temperature. Hence, there are less gas molecules per unit volume, that is the reason why the it is lighter or density is smaller. The website is trying to explain the process of the mechanism of vertical motion of atmosphere caused by adiabatic expansion or shrinkage. There are basically two modes: When the air is near the ground, it is heated and it rise up because it is less dense than that of cold air. During the process of rising, it expands more as the pressure is smaller, then it gets cooled. This called adiabatic cooling. The reverse process occurs on the cold air. You can refer to the ideal gas law and the for basic process of the ideal gas: isothermal(constant T),isobaric(constant P),adiabatic/isotropic(Q=0/constant S) and isochoric(constant V) process. The following link may help you. http://hyperphysics.phy-astr.gsu.edu/hbase/HFrame.html
  14. Maybe you need insert an ammeter in the circuit to get the power which is drawn by the motor. However, you still need to know the efficiency of motor. The simplest way is just read these information from its name plate. Usually, the name plate will specify the normal working voltage, and out power under normal working conditions.. As long as your motor is under normal conditions, the power can be directly read from the name plate. The other way is to conduct a simple experment to calculate the power output like lifting an object with mass m. The gravitational energy gained of the object per unit time equals to the power output if the mass is approriate enough to maintain the motion under constant speed.
  15. As said by DH, it is good for general knowledge but not for research references. It is constantly changing and the reliability is not good enough to be references for a research paper.
  16. A mole of particles refers to the cluster of particles with the number of particle number is the Avogadro constant [math]N_{A}[/math]. Gaseous atoms means that the substance is in gaseous phase, not in other phases like solid,liqiud or aqueous. In the definition of first ionization energy, the restriction of gaseous atoms is necessary becuase the energy to ionize 1 mole of subtance is different in different pahses.
  17. [math]a^2=b^2\Leftrightarrow|a|=|b|[/math] [math]|a|=|b|\Leftrightarrow a=b or a=-b[/math]
  18. Charges always exist. Usually they are inside neutral objects. Once the charges are separated, the system energy is increased because of electrostatic interaction. This situation is not favoured. For the second question, I think the answer probably is yes because there are kinetic energy involved. However, it always need to obey the conservation of charge, energy, momentum, angular momentum and other conservation laws.
  19. I am a bit confused about these two concepts. One example is the X-ray diffraction experiment. I think the principle of X-ray diffraction is interference of X-rays, not the diffraction. why it is called diffraction?
  20. You can refer to the link about diffraction. http://en.wikipedia.org/wiki/Diffraction
  21. comments about what? opinions on Maths, or what your solutions for the exercises?
  22. jian


    It means that mass is another kind of energy. However, the energy is hard to be released. This is the basic principle for fission and fusion reaction. There is a mass difference between the reactants and the products. Then huge amount of energy is released. The problem is that we have to provide large amount of energy to excite the reaction. Also once the reaction occurs, ie exploses and the reaction rate is hard to control. That is the reason why they are used as bombs.
  23. First burning one of the rope, say A, on both sides and one side of the other rope B at the same time. When A is wipes out, burn the other side of B until B finally disappears. From the begining to B burns out, 45mins is obtained.
  24. may be you can use a simple diagram to show the relationship. I cannot provide the rigorous proof yet.
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