What is Conservation: Definition and 999 Discussions

Conservation biology is the study of the conservation of nature and of Earth's biodiversity with the aim of protecting species, their habitats, and ecosystems from excessive rates of extinction and the erosion of biotic interactions. It is an interdisciplinary subject drawing on natural and social sciences, and the practice of natural resource management.The conservation ethic is based on the findings of conservation biology.

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  1. C

    I Spin conservation in the Dirac equation

    Here I am considering the one particle free Dirac equation. As is known the spin operator does not commute with the Hamiltonian. However, the solutions to the Dirac equation have a constant spinor term and only an overall phase factor which depends on time. So as the solution evolves in time...
  2. J

    Law Conservation of Energy: Starting off a solution for 11b

    Homework Statement Homework Equations ΔEsystem + ΔEsurroundings =0 The Attempt at a Solution I have solved 11a and got 5m/s. I can do 11b just by just jumping to Ek = Fs (from the work kinetic energy theorem), but I would like to do it formally from first principles using the Law of...
  3. A

    Analyzing Elastic Collisions w/ Conservation of Energy and Momentum

    Homework Statement There is a 4 kg mass that has a speed of 6 m/sec on a horizontal frictionless surface. The mass collides head-on and elastically with an identical 4 kg mass initially at rest. The final speed of the first 4 kg mass is: (a) 0 m/s (b) 2 m/s (c) 3 m/s (d) 6 m/s Homework...
  4. Ironman1998

    Can energy conservation be violated?

    I think energy can be created...i agree that energy is not conserved between different reference frames..but i can show you that energy measured in a single frame may wary... Does photon's energy increase when i emit it from a train which is moving at comparable speed and get it reflected back...
  5. Zubair Ahmad

    Momentum Conservation: Ball Hitting Pivoted Rod

    If a ball hits a rod at the top which is pivoted at bottom end then is linear momentum conserved?
  6. Zubair Ahmad

    Conservation of Energy: Kinetic & Reference Frames

    If velocity is reference frame dependent then kinetic energy should also be. Considering this we will have different energies in different frames. Doesn't it violate conservation of energy?
  7. Islam Hassan

    I Conservation of Energy on the Cosmological Scale

    Am I correct in understanding that locally, ie, with respect to circumscribable phenomena, conservation of energy is valid in the cosmos but that otherwise it is/may not be? Otherwise said, the source of dark energy does/may not obey this principle? Or is this a question that does not fall...
  8. K

    I Does Conservation Hold True for W Boson Spin Changes during Beta Decay?

    Is this true?: During beta decay a quarks' spin is changed and the mass/ energy difference is converted to a W boson which quickly decays into an electron/positron and an anti neutrino/neutrino. The mass/ energy is conserved through E=mc^2.
  9. Lukeblackhill

    Symmetries and Conservation Laws

    I've been caught by a quite interesting statement of Berkeley physics Course Vol.1 (Chap. 5), that says "In the physical world there exist a number of conservation laws, some exact and some approximate. A conservation law is usually the consequence of some underlying symmetry in the universe."...
  10. C

    Finding angular velocity using conservation of energy

    Homework Statement In the document below I need to try and find the angular velocity I need help on part b Homework Equations F=ma KE_Translational= 0.5mv^2 KE-Rotational= 0.5Iw^2 Assuming g=10m/s^2 The Attempt at a Solution I have the answer key attached with the question but I am not sure...
  11. M

    What is the solution to question 2 on energy conservation problems homework?

    Homework Statement https://www.img.in.th/image/VNYMHY https://www.img.in.th/image/VNYKDv This is my homework,but I have a problems with question no.2 Homework EquationsThe Attempt at a Solution I tried to used energy conservation rule to get that the speed is √2gh ,but I don't know how to know...
  12. G

    D’Alembert Vs Conservation of Energy

    Homework Statement A block with a mass of 5kg is pulled up an incline with a 20 degree incline, the coefficient of friction is 0.2 and the distance 10 metres. The block accelerates from 1m/s at point A to 5m/s at point B. I have to use both D’Alembert’s and Conservation of energy principles...
  13. Catreece

    I On gravity and the conservation of energy

    Alright, so this has been bothering me for awhile, and the more I think about it, the more it bugs me. I'm almost guaranteed wrong about what I'm going to say here, but I'm not sure why I'm wrong, so hopefully someone here can explain my wrongness to me. Unfortunately, this is going to take...
  14. T

    Conservation of Angular Momentum: Hopping onto a Board

    Homework Statement A long board is free to slide on a sheet of frictionless ice. A skater skates to the board (laid horizontally relative to the skater's motion) and hops onto one end, causing the board to slide an rotate. In this situation, are angular and linear momentum conserved...
  15. M

    Conservation of momentum - with understanding

    I just want to state that i DID solve the problem. I just seek understanding of it. I'd be really grateful if someone could answer two of my questions at the end of this post. The problem I've solved here is just to show what I'm dealing with. 1. Homework Statement Object 1 is moving towards...
  16. lc99

    Thermodynamics - Use conservation of energy to answer these questions....

    Homework Statement Homework EquationsThe Attempt at a Solution I understand how they got Q1 and Q2 for the first two columns, but how am i suppose to find Q1 and Q1 for the 3rd and 4th event? Isn't it just 0? Cause it seems like the temperatures just stayed constant. I'm not entirely sure...
  17. M

    Conservation of energy (Waterfall)

    Homework Statement In a waterfall about 20 billion liters of water per hour drop about 110 m. What is the increase of the water temperature, assuming that the entire gain of heat is transferred to the water? Homework Equations I'm more curious about the question in itself. Perhaps I'm missing...
  18. Aleoa

    Intermediate-Calculate a weight using conservation of energy

    Homework Statement This problem comes from the Feynman Lectures. However, the author doesn't explain in detail the procedure to solve the problem. I have to calculate the weight W using only the law of energy conservation. Homework Equations In the second picture W it is lowered of 5...
  19. Nojins

    Conservation of Energy with changing masses on ice

    Homework Statement Mass 1(75kg) glides on ice at 1.8 m/s to a second stationary mass, (52 kg) How far will the pair slide after the collision if the coefficient of kinetic friction between the ice and their skates is .042? Homework Equations Conservation of energy, Kinetic Energy, Work...
  20. K

    Conservation of energy of a perfectly decoherent laser

    The energy and momentum of a closed system is always conserved. If a laser can emit perfectly parallel and perfectly superimposed light waves (occupy the exact same space) that are perfectly 180° out of phase and of the same frequency, what can be said about the energy and momentum of the...
  21. S

    Conservation of momentum & energy

    Homework Statement Hi, I do not know how to resolve question 1d and 2d at all. I hope the rest is well resolved, not sure about 1c and 2c. Can someone check my work and help me resolve problem with this questions, please? Task A hammer of mass 1700kg is dropped 2.5m under its own in fluency of...
  22. P

    I Feynman Diagram-Momentum conservation in primitive vertex

    In the first Feynman diagram, an electron comes in, emits a photon and then leaves. Is this an allowed process? Because if you rotate the diagram by 90o, the diagram should be just as valid, but it doesn't seem to be since it would violate the law of conservation of momentum. So is the...
  23. Jezza

    I Quark mixing and energy conservation

    We've recently been looking at the hadronic decays of the W boson. In this one example, we looked at possible decays for the W boson being produced near its resonance peak, meaning the centre of mass energy is sufficient to produce u,d,c,s & b quarks. However, because we're below the mass of...
  24. S

    I Understanding Spin and Helicity Conservation in Relativistic Interactions

    I am a bit confused about spin conservation at relativistic energies. I am reading a QFT book by Peskin and at a point he specifies that "In the nonrelativistic limit the total spin of the system is conserved". Later when we go to the relativistic limit (there is the interaction between a photon...
  25. E

    Momentum and energy conservation in a vertical loop

    Homework Statement Two beads with masses of M and m are threaded on a vertical loop with radius of R. M is released without velocity from a height of 1.5R from the bottom of the loop. The collision between the beads is completely elastic. What is the smallest mass M that will make the second...
  26. Nick tringali

    Is the Law of Conservation of Mass Always Obeyed?

    Are the laws of conservation of mass always obeyed. in a nuclear reaction mass is converted to energy therefore mass isn't conserved. I understand that energy is always conserved, but I feel like mass isn't.
  27. physea

    Understanding Momentum Conservation: Exploring Kinetic Energy and Its Effects

    I read that kinetic energy may not be preserved, but momentum must always be preserved. How can that be? If there's a loss in kinetic energy due to friction or heat, the velocities will be reduced thus momentum will be reduced?
  28. J

    A Helicity conservation in scattering

    Hi, My question basically comes from this book called "Deep inelastic scattering" In the second chapter, it first made a similar argument for J = 1 Jz = -1, +1 which is pretty easy to get along with. However, immediately following from that there was this argument which confuses me a bit...
  29. KieronB

    Conservation of energy question -

    A cylindrical container of water has a diameter of 7.98 m and a perpendicular height of 2 m. It is filled with water (1000 kg = 1000 l) and placed on top of a 4 m stand. Calculate the: A) potential energy of the water B) kinetic energy of 20 kg of water just before it reaches the ground, if the...
  30. Wes Turner

    Conservation of energy in x vs y direction

    Homework Statement A child goes down a water slide. The slide is 9.0 m tall. She pushes off with an initial speed of 2.0 m/s (in the horizontal direction). If the slide is frictionless, how fast will she be going at the bottom of the slide? Homework Equations In the book, they use a...
  31. M

    Fluids: Continuity and Conservation of Mass

    Hi PF! In fluids I've noticed many authors use the continuity equation with an integral form of conservation of volume (assume density is constant). Is this double counting? Example: let fluid velocity inside an idle bubble be ##\vec u = \nabla \phi##. Conservation of mass implies ##\nabla u =...
  32. G Cooke

    Conservation of electrical energy on a conductor

    I'm having trouble seeing how electric potential energy production on a conductor follows conservation of energy. Let's use the photoelectric effect as an example. A photon with energy E = hν strikes a conductor, ejecting a photoelectron with a maximum kinetic energy of hν - φ. Assuming the...
  33. F

    Energy conservation in circular motion

    Homework Statement An object of mass m = 1 kg moves along a circular frictionless path of radius R = 0.5 m from point A to point B at which it makes an angle θ with the vertical direction as shown in the figure. If the object is release from rest (VA = 0) and θ = 30° , what is the normal force...
  34. F

    Conservation of Energy: block on a table

    Homework Statement Homework Equations ∑F=ma W = - ΔUs ΔUs = 0.5 k (xƒ)^2 - 0.5 k (xi)^2 W = ΔUs + ΔKE d = viy t + 0.5 * t^2 * a The Attempt at a Solution A) [/B]W = - (0.5 k xƒ^2 - 0.5 k xi^2) = - (0-100) W = 100 J B) W = ΔUs + ΔKE 100 = 0.5 m vf^2 -0 + 0 - 0.5 k xi ^2 100 = 0.5 * 2 * vf^2...
  35. F

    Conservation of Energy -- Toy car hits and compresses a spring

    Homework Statement A toy car has a mass of 2 kg moves with initial speed of 2 m/s on a rough horizontal plane of μκ=0.14.A spring with constant of 250 N/m is fixed. Which of the following statements is true ? A) The toy does not approach the spring B) The toy just touch the spring[/url][/IMG]...
  36. entropy1

    Photon absorbtion and conservation

    If a (polarized) photon is absorbed by a polarization filter, does its energy go into the filter? I am wondering if that is the case to obey conservation laws. And if it passes, is its original polarisation direction somehow conserved?
  37. H

    Mechanics - Hooke's law and energy conservation

    Homework Statement One end of a light elastic string of stiffness mg/l and natural length l is attached to a point O. A small bead of mass m is fixed to the free end of the string. The bead is held at O and then released so that it will fall vertically. In terms of find the greatest depth to...
  38. C

    How does the conservation of electrostatic energy work?

    A charge of +2.5 micro coulomb is at the origin and a +3.5 micro coulomb is at the point (3,0). What is the velocity of a proton when it is at (6,0) if it was released at (5,0). My solution: $$E_0=E_f$$ $$PE=KE$$ $$Since...Work = -PE$$ I can calculate the work it takes to move the proton from...
  39. I

    Is Velocity Conserved in an Elastic Collision Between Two Cars?

    My question is, in an explosion, where 2 cars at rest are pushed apart by a spring between them, is velocity conserved? Does the total velocity for both cars before spring release equal the total velocity after release? Why or why not?
  40. O

    Conservation of energy/Angular momentum for elastic collison

    Homework Statement A uniform thin rod of Length L and mass M can freely rotate about a point 0 and is at rest in at the vertical. A ball of mass m on a light string of length R, which is also attached about the pivot is deflected by a small angle from the vertical and let go of. If the...
  41. L

    Conservation of energy problem

    Homework Statement Homework Equations W spring = 1/2kx^2 Ug = mgh The Attempt at a Solution I have the work in the above problem, but I'm kinda confused how there is any potential energy here besides the spring potential energy that we get in the final state. Why is mgh here mgx? why can h...
  42. D

    Combining conservation of momentum and kinetic energy

    Hi everyone, hopefully someone will be able to point me in the right direction with this problem, I get as far as combining the two equations together and no matter how I rearrange them they don't seem to cancel nicely and leave me with an awful quadratic, I can find vx, but the question...
  43. L

    Is this a conservation of energy problem?

    Homework Statement I'm sorry but I don't have the exactly problem written down but I know the givens. So the question involves finding work done on a pendulum hanging from the ceiling. Homework Equations I was given the the length of the string is 1m. That a mass hangs at the bottom of...
  44. S

    I Velocity addition and conservation of the energy

    Hello everyone, For some time I'm a little bit confused about (at the first view) a very simple question, which is about the conversation of the energy of moving objects (in terms of special relativity). As an example let's talk about firearms. If the mass of the gun M1 is infinitely higher...
  45. G

    B Casimir effect, energy conservation

    I was reading some articles about Casimir effect. It turns out that some virtual particles are created and suddenly disappears amd that these particles can exert a pressure on the plates. It seems that this creation breaks energy conservation law, but it cannot be.I would like to know which...
  46. Anonymous123451234

    Conservation of mechanical energy

    Derive equation v= √((2gh)/(1+.5(m/M)(r/R)^2)) by applying conservation of mechanical energy. A string is attached to a hanging mass and wrapped around a small cylinder. The hanging mass is released from rest from an initial height (h) and accelerates to the floor. The theoretical velocity (v)...
  47. Kate2018

    High School Physics Question -- Skateboarder Jumps & Conservation of Momentum

    Homework Statement Lee is riding on her 6 kg skateboard with a constant speed of 2 m/s. She jumps off of her skateboard and continues forward with a velocity of 4 m/s relative to the ground. This causes the skateboard to go flying forward with a speed of 18.5 m/s relative to the ground. What is...
  48. Jenna

    Using Energy and momentum conservation to derive the equation

    Homework Statement I need to find the intial velocity of a ball, given the angle the pendulum bob swings through. I need to derive this equation. [/B] V0=4.43mtotalL1/2{1-cosΔθ}1/2/mball Homework EquationsThe Attempt at a Solution I have barely any attempts since I can't even think where to...
  49. R

    Why is conservation of angular momentum failing in this case

    https://drive.google.com/file/d/1Z-avhDqYbxDtMzk6Rv_NES7rIvDmzMPz/view?usp=drivesdk 2.conservation of angular momentum 3.for the above question I tried applying conservation of angular momentum about the point of contact where the cyclinders touch each other but my answer does not match with...
  50. S

    Conservation of Angular Momentum and a Spinning Bicycle Wheel

    A person standing on a stationary friction-less turntable spins a bicycle wheel with the rotation axis of the wheel in the horizontal direction, thus the initial angular momentum is in the horizontal direction (x - axis), say to the right. Now suddenly the person turns the axis of rotation of...
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