Change Definition and 1000 Threads

  1. S

    Change in ground state energy due to perturbation

    Homework Statement Consider a quantum particle of mass m in one dimension in an infinite potential well , i.e V(x) = 0 for -a/2 < x < a/2 , and V(x) =∞ for |x| ≥ a/2 . A small perturbation V'(x) =2ε|x|/a , is added. The change in the ground state energy to O(ε) is: Homework Equations The...
  2. A

    Change of pressure simple cylinder

    I am trying to calculate the spring rate for an air filled shock-absorber, however I am struggling to get my head around the change non-linearity at the start of compression. Obviously if the shock is fully extended then it will be applying no compressive force to the chassis so that accounts...
  3. CAH

    Why does the magnetic field/flux change in copper conductor?

    If you drop a permanent magnet like steel through a copper tube it induces an emf, this is because you have a change in magnetic field/flux? But how? Why? The copper isn't producing a current before the magnet is dropped into it... Does something happen with the electrons in the copper?
  4. Revengeance

    Calculating Tire Pressure Change with Temperature Increase

    An automobile tire has a pressure of 210kPa at 20.0 degrees celsius. What will be the tire pressure after driving for some time if the temperature rises to 35.0 degrees celsius. The equations we have are P1*V1/T1 = P2V2/T2 V1/T1=V2/T2
  5. H

    Orbital stability and fictitious potential energy with a change of convention

    The condition for a stable orbit is given by (3.42), where ##V'## is the fictitious potential energy (potential energy of the corresponding fictitious one-dimensional problem) and ##r_0## is the radius of the circular orbit. The result ##n>-3## is obtained by using the convention that positive...
  6. Logic Cloud

    I General notion of coordinate change

    I'm trying to understand the nature of coordinate transformations in physics. In classical mechanics, we can transform to a different coordinate frame by means of a Galilean transformation. In special relativity, this is replaced by a Lorentz transformation. I am now wondering whether there...
  7. M

    Find entropy change when two tanks equalize

    Homework Statement Two rigid, insulated tanks are connected with a pipe and valve. One tank has 0.5 kg air at 200 kPa, 300 K and the other has 0.75 kg air at 100 kPa, 400 K. The valve is opened, and the air comes to a single uniform state without any heat transfer. Find the final temperature...
  8. normal_force

    KE1 vs KE2, mechanical energy change

    Homework Statement If two objects of unequal mass and unequal Kinetic energy hit each other, they lose some energy to other forms but keep enough to do Work on each other. A good example is a car and wind, a man and ball could also apply, a ball with KE could stop a running man if KE does work...
  9. H

    B Recast a differential equation with a change of variable

    I obtained an extra factor of ##\frac{1}{l^2}## in the first term on the LHS of (3.34). From (3.33), LHS ##=u^2\frac{d}{d\theta}(\frac{u^2}{m}\frac{du}{d\theta}\frac{dr}{du})-\frac{l^2u^3}{m}## ##=u^2\frac{d}{d\theta}(-\frac{1}{m}\frac{du}{d\theta})-\frac{l^2u^3}{m}##...
  10. FruitNinja

    ORBIT: change in orbital distance

    Homework Statement we know the mass of the moon, Mm, and the Earth's, Me, and also the initial distance between their centers as the moon orbits the earth, Rem. Now if the earth’s angular velocity about its own axis is slowing down from a initial given angular velocity, ωi to a final angular...
  11. Tom MS

    Does Wave Refraction Change Wave Direction or Alignment

    I can't seem to find anything online that talks about this distinction. I understand how when the water gets shallower that part of the wave gets slowed down so the overall alignment parallels with the shore. However, I wouldn't think that would change the actual direction of the wave. I need a...
  12. Maka42

    Velocity change due to load dropped vertically onto trolley

    A trolley is moving at a constant speed down a track, with no net force acting upon it. A heavy load is dropped vertically on top of the moving trolley. What happens to the trolley's speed? a) It stays the same, b) It decreases, c) It becomes zero, d) It is impossible to say, e) It increases...
  13. N

    B Neutrino change of flavour and conservation of energy

    Hello, I have a simple question. Has the discovery that some neutrinos change their flavor posed any issues with conservation of energy?! How has this been solved?! Thank you.
  14. hackhard

    B Can Force Change Mass w/ Constant Velocity?

    can a resultant external force on a body change its mass but keep velocity of its centre of mass constant ? Is it practically possible - ##\vec{F}_{ext}=\vec{v}_{com}\frac{\mathrm{d} M}{\mathrm{d} t}## where F is nonzero
  15. Giu1iano

    Change in velocity due to force acting over given time

    What change in velocity would be produced by an unbalanced force of 2.4 × 10^4 N acting for 6 s on a 2.0 × 10^3 kg dragster? Not sure how to setup this problem Equations i have are as follows: Fnet = mass × acceleration Velocity2 = velocity1 + acceleration × time Distance = velocity1 × time +...
  16. Jason Sylvestre

    I Gradient Vector- largest possible rate of change?

    Hello, My professor just gave us a True or False problem that states: ∇H(x,y), the gradient vector of H(x,y), gives us the largest possible rate of change of H at (x,y). Now, he said the answer is true, but it was my understanding that the gradient itself gives the direction of where the...
  17. saybrook1

    Trouble with an index change in Laurent series

    Homework Statement Hey guys, I'm just going through a Laurent series example and I'm having trouble understanding how they switched the index on a summation from n=0 to n=1 and then switched the argument from z^(-n-1) to z^n as well as changing the upper limit to -infinity. If anyone could shed...
  18. F

    Quantum Mechanics: Delta Potential Sudden Change

    Homework Statement I have a particle which is initially in a bound state for a given voltage in the form of a delta function at the origin, V = -αδ(x) initial state is ψα = (√αm)/h2*exp(-m*α*|x|/(h2) At t=0, voltage is changed to V = -βδ(x) both α and β are greater than zero. Right now I'm...
  19. T

    How can heat change if temp is constant?

    In my textbook it says an isothermal process occurs when the temperature is constant. It also said taht typically, Q,W, and delta U are not 0 in these processes. My question is how can heat not be 0 if temperature is constant? Q=mcDeltaT so if Delta T is 0, then Q also has to be 0 right?
  20. F

    International Change Electric Charge Day

    Hello. What would you think of the international scientific community calling to change all negatively charged particles to positive and vice versa? Do you think there's a circumstance where we should switch or should have switched? The only reason I brought this up is that it came up when...
  21. V

    Change in time period of pendulum

    Homework Statement Q The length of a simple pendulum executing SHM is increased by 21% .The percentage increase in the time period of the pendulum of increased length is a) 11% b) 21% c)42% d)10% Homework Equations ##T = 2\pi\sqrt{\frac{L}{g}}## The Attempt at a Solution ##T^2 =...
  22. G

    MHB Change of Basis: Exploring Basis Vectors in $\mathbb{R}^3$

    Consider the following set of vectors in $\mathbb{R}^3:$ $u_0 = (1,2,0),~ u_1 = (1,2,1), ~u_2 = (2,3,0), ~u_3 = (4,6,1)$ Explain why each of the two subsets $B_0 = \left\{u_0, u_2,u_3\right\}$ and $B_1 = \left\{u_1, u_2, u_3\right\}$ forms a basis of $\mathbb{R}^3$. If we write $[\mathbf{x}]_0$...
  23. E

    Required heat, entropy change of object dropped in water

    Homework Statement A 1 liter container is filled with argon to pressure of 10^5Pa at 303K. Dropped into pool at temp 323K. How much heat is needed to heat the gas to 323K? what is the entropy change in the gas and the universe? ignore the entropy change in container. Homework Equations...
  24. Z

    Change in Radius of star during core contraction

    Homework Statement We can make a rough estimate of how much the envelope of a red giant should expand as a result of the contraction of its core based on conservation of energy. We will consider a star of mass M and initial radius R, with a core of mass Mc and radius Rc. We will focus on the...
  25. Elena14

    Temperature change in ice water interface

    A metal block at 500 K is kept on a large ice slab at 273 K.The metal block completely sinks inside the ice slab. I was told that the water in contact with ice would not change its temperature while the block sinks down and hence the "only" heat transfer from the metal block to ice slab will...
  26. R

    Relationship of bulk modulus and fractional volume change

    So my question is, if the bulk modulus change by 5%, what is the fractional volume change value? is it times 0.05 or divided by 0.05? or the fractional volume change still the same?
  27. A

    Calculating Delta P in Vacuum Chambers: P1 or 0?

    in calculating the delta p in vacuum chambers do we substitute p1 with 0 or the whole equation doesn't exist if air doesn't exist?
  28. L

    How to change density of states to eV

    I know that if I multiply e^3/2 (e= 1.602x10^-19) to the unit below I can change it to eV Can somebody help me I don't know why
  29. R

    Multivariable calculus: find the rate of change

    The problem is: The temperature (in degrees Celsius) of a metal plate, located in the xy -plane, at any point (x, y ) is given by the function of two variables T(x, y ) = x sin y + y2 sin x. (a) Find the rate of change in temperature in the direction of the positive x-axis at the point (π, π)...
  30. A

    What causes stagnation pressure to change?

    For a real mass-conserved(m dot is constant throughout the system) steady-state mono-substance(same substance throughout) flow , what are the different factors which can cause stagnation pressure and temperature to drop/rise?
  31. S

    Entropy change in a reversible isothermal process

    Why does ∆S = 0 for a reversible process, but for a reversible isothermal process, ∆S is given by nRln(Vf/Vi) (or other variations of that equation)?
  32. Y

    Does negating a set change it symbolically?

    So I have to prove "If (AxB)∩(BxA) ≠ ∅, then (A∩B) ≠ ∅." I wanted to prove by changing it's form. P = (AxB)∩(BxA) ≠ ∅ and Q = (A∩B) ≠ ∅ . The conditional statement is P implies Q and the new statement is not P or Q . P → Q = ¬ P∨Q They are equivalent. But how do I negate P? Would it be...
  33. Philip Koeck

    Why can one calculate entropy change for thermal conduction?

    A hot object in thermal contact with a cold one will finally reach a temperature in between. Why can the entropy change of each object be calculated as if the process was reversible? Is there a reversible process with the same final and initial state and what would that be?
  34. G

    What is the final pressure in the balloons after being disconnected?

    Homework Statement Two balloons are connected by a faucet. Gas in the first balloon is at pressure p_1=100kPa, and in the second is p_2=0,5MPa. Volumes are V_1=0,12m^3 and V_2=0,5m^3. Temperature of a gas is constant. Find pressure in balloons p after faucet is opened (balloons are not...
  35. A

    Force and rate of change of momentum

    My question is simply..if force does equate to the rate of change of momentum, then why is it not taughted as this rate rather simply a push or pull? Is it becuase really they are the same thing and it is much easy to explain/work with? Just curious Guess up until now I didn't even think of...
  36. Superposed_Cat

    What causes paint to change colour over time?

    What compounds,reactions and factors cause modern day paint to change hue intensity over time? Any help appreciated.
  37. C

    Translate change of length to force in hanging chain problem

    I'm trying to write a simple script in blender python in order to show load deflection in cloth simulation. My question is: Is it possible to translate the change of length (distance between two nodes), into a force? (Newton between those nodes)? In addition you will find a minimal example. The...
  38. O

    Change the FAQ? Also, how can 0-volume objects collide?

    (1) Maybe should've messanged this, but given LIGO, the FAQ might need a light edit. It says, "Gravitational waves have never been detected directly, but the loss of energy from the Hulse-Taylor binary pulsar has been checked to high precision against GR’s predictions of the power emitted in...
  39. O

    Irreversible adiabatic process - is the entropy change zero?

    Homework Statement A well insulated container consists of two equal volumes separated by a partition - one half an ideal gas while the other is a vacuum. The partition is removed, and the gas expands. What is the entropy change per mole? Homework Equations dS = dQrev/T S/R = Cp/R dT/T -...
  40. B

    2nd derivative change of variables

    Let's say ##f(x)=ax^2##. Then ##d^2f/dx^2=2a##. Now we can make the change of variables ##y\equiv\sqrt ax## to give ##f(y)=y^2##. Then ##d^2f/dy^2=2##. It follows that ##\frac{d^2f}{dx^2}=a\frac{d^2f}{dy^2},## but I can't replicate this with the chain rule. I would put...
  41. A

    What causes orbits to change over time?

    There are two examples: A planet rotating around a star and a spacecraft maneuvering through space. Let's assume that solar radiation has no affect on the spacecraft and the spacecraft is not bumping into any stuff, and niether is the planet; and no other gravitational sources are involved...
  42. x2017

    Change in Velocity after a Collision

    Homework Statement Kevin and Jake collide in the air. If Kevin undergoes a 4.2 kg*m/s change in momentum, what is Jacob’s change in velocity if he has a mass of 83.2 kg? Homework Equations p=mv MV+mv=MV'+mv' The Attempt at a Solution I tried the simplest way possible... p=mv v=p/m v=4.2/83.2...
  43. N

    Thermodynamics phase change question

    My thermo teacher was talking about 2 phase rankine cycles and he said the once water boils at atmospheric pressure its temperature can not get higher than 212 no matter how much heat you add. He said the only way you can raise the temperature of steam past 212 F is the raise the pressure. Why...
  44. ramzerimar

    Should I stay in MechE or change to Electrical?

    Hey people. First of all, I'm now in the third semester of my course in Mechanical Engineering. I have interest in aerospace/aeronautics, so there are plenty of things in mechanical that I like - fluid mechanics, aerodynamics - and that was the reason I choose this undergrad. Nonetheless, I do...
  45. R

    Determining change in internal energy and enthelpy

    Homework Statement A 1 m3 rigid tank has propane at 100 kPa and 300 K. The tank is connected to another 0.5 m3rigid tank which has propane at 250 kPa and 400 K by a ball valve. The valve is opened and both tanks come to a uniform state at 325 K. Calculate the change in internal energy and...
  46. O

    Conditions for change of order in derivative of a partial

    Sorry about the title, had a hard time trying to fit the question on the given space. The question is quite simple : If F = F(x_1,...,x_n,t) , Under what conditions is \frac{d }{dt} \frac{\partial F }{\partial xi} = \frac{\partial }{\partial xi} \frac{dF }{dt} true?
  47. empty_set

    Change in density due to thermal expansion

    Homework Statement I want to find the mathematical proof to show that the density of an object changes with thermal expansion. My professor showed this in class and it was horribly wrong because he let a few things out. The book I'm reading showed it in 4 steps and left out a lot of the crucial...
  48. W

    Change in Momentum of shopping cart

    Homework Statement A 12kg shopping cart rolls due south at 1.5m/s. After striking the bumper of a car, it travels at 0.80m/s at 30. degrees E of South. What is the magnitude and direction of the change in momentum sustained by the shopping cart? Homework Equations p = mv The Attempt at a...
  49. B

    Does the inertia of an object ever change?

    If the mass of an object is the same, does the inertia ever change. For example, is the inertia of a person different if they are on the surface of the Earth than if they are orbiting Earth or in outer space?
  50. R

    Understanding Deceleration: Investigating the Force and Energy Changes on a Ship

    Homework Statement 1.If the ship has a mass of 2.5 x 10^7 kg calculate the magnitude of the force acting on the ship during the deceleration. I was trying to work that out using f=ma but that would Make the force negative , is that possible 2. What is the nature of the force acting on the...
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