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. ubergewehr273

    Doubt on conservation of angular momentum

    Homework Statement A uniform thin rod of length ##2l## and mass ##m## lies on a horizontal table. A horizontal impulse ##J## is given to the rod at one end. There is no friction. The total kinetic energy of the rod after impulse will be ? Homework Equations ##Jl=I\omega## ##J=mv_{cm}##...
  2. W

    By energy conservation, show the 4-velocity of dust satisfies this....

    Homework Statement Using conservation of energy, show that the 4-velocity ##u^{\mu}## of dust satisfies: ##u^{\mu}\nabla_{\mu}u^{\nu} = f u^{\nu}## Explicitly identify ##f##, which is some function of ##u^{\mu}##, ##\rho## and their derivatives. And show that this equation becomes...
  3. V

    Conservation of Energy and projectile motion

    I am finishing up a lab write up for conservation of energy, where we launched a projectile into the air and measured the initial velocity and height of the projectile. ( 10 trials) One of my questions asks if I wanted the ball (projectile) to travel twice as high, how much faster would it have...
  4. S

    I CPT Violation and Energy Conservation: Explained!

    Hello! I read that natural processes are invariant under CPT (based on some theorem) and that CP violation was observed experimentally. So this would mean that there are processes that are violated under time reversal. However, based on Noether theorem, this would mean that the energy is not...
  5. C

    Conservation of Energy: Spring pushing a block up an incline

    Homework Statement "Consider a 250 gram block on a 10 degree frictionless incline and in contact with a spring of constant 1.2 N/cm. If the block is launched from rest by the spring with an initial compression of 6cm, how fast is the block moving at the point of release from the spring? How...
  6. S

    I What is the Conservation of Information in Quantum Mechanics?

    Hi everyone, I was watching Susskinsd's lectures posted on youtube about Quantum mechanics and he started explaining his -1st basic law of physics saying: the conservation of information means basically that if you start with 2 quantum states (vectors) which are observably different, or...
  7. M

    Why do 2 d not decay into alpha particle and neutral pion?

    Homework Statement The reaction dd → απ0 (where α is the Helium-4 nucleus and d denotes the deuteron) has never been observed. Why? Homework EquationsThe Attempt at a Solution [/B] So I checked first the masses to make sure energy/momentum are conserved and found out that mass of 2d is...
  8. K

    Is the Law of Conservation of Energy Valid in a Non-Local Context?

    Is it accepted that the law of conservation of energy can be considered in a non-local context? If this is not accepted, then why not?
  9. C

    MHB Using the idea of conservation of energy

    Dear Everybody There is a ball which has mass of 11 grams is thrown straight up with an initial speed of 4 m/s. Assume the air drag is negligible. a. What is the kinetic energy of the ball (in J) as it leaves the hand? b. How much work is done by the gravitational force during the ball's rise...
  10. Cocoleia

    Conservation of Power in the armature circuit of a DC motor

    Homework Statement I am asked in a lab report to explain the conservation of power in the armature circuit of the DC motor. Homework Equations This is the data I have acquired: The Attempt at a Solution I have been reading around, and I have learned somewhat about the Armature Copper Loss...
  11. R

    Conservation of energy -- Two charges separated by a spring

    1. Two identical charged particles which are point masses are fastened to the two ends of a spring of spring constant 100 N/m and the natural length 10cm.The system rests on a smooth horizontal table.The charge of each particle is 2*10^(-8)C.the extension of spring if the extension is small as...
  12. T

    Confusion with "explosive" part, Conservation of Momentum

    Homework Statement A two-stage rocket is traveling at 4500 m/s before the stages separate. The 3000-kg first stage is pushed away from the second stage with an explosive charge, after which the first stage continues to travel in the same direction at a speed of 3000 m/s . How fast is the...
  13. F

    Conservation of Momentum With Changing Mass

    Homework Statement [/B] A rocket that starts at rest with mass M ejects exhaust at a given speed u. What is the mass of the rocket (including unused fuel) when its momentum is maximum? What is the mass when its energy is maximum? Homework Equations [/B] p = mv The Attempt at a Solution...
  14. G

    Train Conservation of Energy Question

    I go to work on the train and I get on at the back and get off at the front. I can choose when to walk through the train. If I walk when the train is accelerating forwards it is harder for me to get to the front and I do more work. If I make the trip when the train is stopped or at a constant...
  15. W

    Conservation of Buoyancy: Explained & Applied

    Hi, all and thanks for your time. I did read that the conservation of Buoyancy is an "alternative" conservation of energy under some hypothesis. Can someone explain how do I start from the conservation of energy and find the conservation of buoyancy? Are there some corresponding mathematical...
  16. K

    Conservation of Momentum Lab (Carts Collide and Stick Together)

    Homework Statement We did a lab where we had one cart with an unknown mass stationary on a friction-less surface. Another cart with a mass of 378.9g, was pushed down the track (which moves at a constant speed due to the friction-free surface) and collides with the second cart - so it is a hit...
  17. P

    Dust in special relativity - conservation of particle number

    Homework Statement My textbook states: Since the number of particles of dust is conserved we also have the conservation equation $$\nabla_\mu (\rho u^\mu)=0$$ Where ##\rho=nm=N/(\mathrm{d}x \cdot \mathrm{d}y \cdot \mathrm{d}z) m## is the mass per infinitesimal volume and ## (u^\mu) ## is...
  18. O

    I Photonuclear reaction & Conservation of momentum

    γ+2D ----> 1H + 1n In this photonuclear reaction, is it possible to write the momentum balance equation as it follows, MHvH = Mnvn It somehow seems to wrong to me, since the incoming photon has a certain momentum, which is not taken account in the balance equation. Thank you in advance.
  19. E

    SHM Energy Conservation in a Spring

    1. The problem statement, all variables, and given/known data Describe the energy conversions in a spring undergoing simple harmonic motion as it moves from the point of maximum compression to maximum stretch in a frictionless environment. Focus on points at which there will be maximum speed...
  20. F

    What is the final velocity of a sail after being hit by photons from a star?

    Homework Statement The luminosity of the star is defined as ##\phi = L/4\pi r^2## The photons from the star hits the sail of mass ##M## and cross sectional area ##A##. What's the final velocity of the sail after getting hit by photons for a small time t? Assume the collision is elastic and the...
  21. U

    Conservation of linear momentum in this system

    A pet mouse sleeps near the eastern edge of a stationary, horizontal turntable that is supported by a frictionless, vertical axle through its center. The mouse wakes up and starts to walk north on the turntable. Is the momentum of the system constant? i understand that the initial momentum is...
  22. C

    Conservation of Linear Momentum and Covariance

    Homework Statement Assume two masses m1' and m2' are moving in the positive x-direction with velocities v1' and v2' as measured by an observer in S' before a collision. After the collision, the two masses stick together and move with velocity v' in S'. Show that if an observer in S' finds...
  23. Lukanol

    Conservation of momentum on relativistic collisions

    1. Homework Statement ( This question is from the textbook of Introduction to Elementary Particle Physics, written by Griffiths, on the problem set of Chapter 3 ) Particle A (energy E) hits particle B (at rest), producing particles C1, C2, ...: A + B → C1 + C2 + ... + CN. Calculate the...
  24. S

    Conservation of Momentum vs Energy

    Homework Statement Given a horizontal rod (parallel to x axis) and two disks attached near its ends symmetrically. The rods and disks are perfectly balanced i.e. the disks have same mass and density. The system's center of mass is exactly at geometric center of the rod (since its balanced)...
  25. LarryS

    I Conservation laws during particle decay?

    I believe that conservation laws, like for energy and momentum, are obeyed during the particle decay process, e.g. the total energy of the new output particles is equal to the energy of the one input particle. But is that relationship subject to quantum fuzziness? Suppose we, somehow, prepare...
  26. A

    Conservation of angular momentum - change of inertia

    Recently I was searching the internet and books for the connection between conservation of angular momentum and conservation of rotational energy and found nothing. Let's say an ice skater rotates and draws the arms in - the rotation speeds up. The rotational energy must increase because the...
  27. C

    Other Physics EE (Extended Essay) Advice: Conservation of momentum

    I am not sure if I am at the right place and I hope that I am... For my EE I want to do an investigation on something related to pool table and games so it will definitely be related to momentum. And one of the common techniques in pool games is that the player aims the ball on the rail of the...
  28. A

    I Energy conservation concerns in the weak interaction

    I have a few questions: Can a u quark turn into a d quark (heavier) via the weak interaction? If so, how is the mass/energy shortfall made up? How can the (supermassive) carrier bosons (W, Z) be called into being? Where does the energy come from? Or is the energy bill unpaid because they are...
  29. Alexander350

    Finding angular speed by conservation of angular momentum

    Homework Statement Homework Equations Angular momentum = moment of inertia * angular velocity Change in angular momentum = impulsive moment v^2=u^2+2as The Attempt at a Solution First I used v^2=u^2+2as to find the velocity of the particle the moment the string goes taut. I got v=\sqrt{8ag}...
  30. S

    Conservation of Momentum for Magnets

    Homework Statement Given 2 magnets of equal weight (w0) and each with a magnetic strength (t0) placed inside a straight hollow cylindrical tube. One of the magnets is attached to one end of the tube and the other magnet is free to move inside the tube. The other end of the tube is open to...
  31. person123

    Conservation of Energy for Unwinding Mass

    As a spinning mass is unwound, angular momentum is conserved, meaning ##Iω## remains constant. However, since rotational energy is proportional to the square of the angular velocity, how is it possible for energy to be conserved as well?
  32. B

    Conservation of Angular Momentum of Train on Disk

    Homework Statement A horizontal plywood disk with mass 6.90 kg and diameter 1.14 m pivots on frictionless bearings about a vertical axis through its center. You attach a circular model-railroad track of negligible mass and average diameter 1.04 m to the disk. A 1.40 −kg , battery-driven model...
  33. DoobleD

    I Dark energy and conservation of energy

    From what I can read on the web, it seems poeple don't agree wether or not dark energy violates conservation of energy. For some, as dark energy density is constant and the Universe expands, the total energy grows. For others, that growing energy is compensated by a growing negative...
  34. deuce123

    Conservation of angular momentum

    Homework Statement A 220-kg beam 2.8 m in length slides broadside down the ice with a speed of 23 m/s . A 68-kgman at rest grabs one end as it goes past and hangs on as both he and the beam go spinning down the ice. Assume frictionless motion. (Figure 1) Homework Equations L1=L2 Iω=L The...
  35. C

    Directional conservation problem with E=cB?

    As I understand it, the ratio of the electric field strength to the magnetic field strength at any point in a propagating electromagnetic plane wave is equal to the speed of light. How can the electric and magnetic field be perpendicular to each other yet still validate the E = cB equation? A...
  36. I

    Two-ended rocket - Conservation of Momentum

    Homework Statement A two-ended "rocket" is initially stationary on a frictionless floor, with its center at the origin of an axis. The rocket consists of a central block C (of mass M=6 kg) and blocks L and R (each of mass m = 2 kg) on the left and right sides. Small explosions can shoot either...
  37. S

    Conservation of Work/Momentum of Puck Sliding Off Plate

    Homework Statement I saw this problem from a few years ago here on Physics Forum (https://www.physicsforums.com/threads/work-energy-theorem-problem.823990/) and wanted some clarification. Here is the problem: A curved plate of mass M is placed on the horizontal, frictionless plane as shown...
  38. O

    Energy Conservation: Puck on Wood on Frictionless Surface

    Homework Statement Hey all, another problem. There is a 1 meter wooden panel that is on a frictionless surface. A puck is placed on one end of the panel and is pushed towards the other side. The mass of the panel is 10 times that of the puck. Also, there is a friction coefficient of uk=0.15...
  39. O

    Conservation of Energy: Pulley and Springs

    Homework Statement Two blocks are connected with a massless, non-stretchable rope, and connected to a spring that is fixed to a wall. One of the blocks is hanging from the side of the table, while the other lies on the table. The mass of each block is m=1.0 kg, spring stiffness is k=50 N/m...
  40. C

    Energy conservation in a magnetron

    I am trying to understand how energy is conserved in a magnetron. If the electrons are following a circular path in the magnetic field and never reach the anode will there be zero current between the anode and the cathode? If so how does the device consume power from the external circuit...
  41. Undacuva

    Underpinnings of conservation of energy/mass

    I understand the 1st law of thermodynamics developed as a generalization based on experimental observations, in that an exception has yet to be found in thousands of situations, so it is considered to hold true in all possible situations. If that is how it developed, is there any other theory or...
  42. C

    Apparent violation of momentum conservation in EM

    We have two cylindrical shells (with radii a and b and charges +Q and -Q) along the z-axis. There is a uniform magnetic field (in the positive z-direction) out to radius r from the z-axis. Because of the symmetry, the total field momentum is zero. Suppose we now connect the shells using a wire...
  43. SlowThinker

    Using laser to overcome conservation of etendue

    I was watching a video where the author (Isaac Arthur) says it's possible to use mirrors and lens around a star to focus the energy to boil a planet on the other side of the galaxy. At first it sounds reasonable, surely you have enough energy, but I have doubts that mirrors would be able to do...
  44. Richardparker800

    Need help with collision and conservation of momentum problem

    Homework Statement Two blocks move along a horizontal frictionless surface and collide head-on with each other. The mass of the first block, moving to the right with speed v is m, and the mass of the second block moving towards the left with speed 3v is 2m. After the collision, the block of...
  45. G

    Momentum Conservation & External Force: Explained with an Example

    Why ain't momentum conserved when external force acts on the system? Please explain with an example.
  46. Pbaseball

    Conservation of momentum and Moment of Inertia

    Hello everyone, I'm needing help understanding how to take the conservation of momentum equation and substitute moment of inertia inplace of mass in the equation. I understand this is a linear equation and I'm trying to incorporate angular momentum. I just want to determine the speed of the ball...
  47. M

    Conservation of Mass Fluids Wave

    Hi PF! Suppose we have a water wave with mean depth ##H## with disturbance ##\zeta## above/below ##H## propagating through a channel of thickness ##b##. The book parenthetically remarks that the continuity equation becomes $$\partial_t(b(H+\zeta))+\partial_x(bHu)=0.$$ However, when I try...
  48. Lunct

    B Can the law of conservation of energy of be broken?

    A consequence of Heisenberg's Uncertainty principle is that particles energy level can fluctuate their amount of energy, e, for a short amount of time, t, as long as e x t < h/4pi (where he is = to Planck's constant). So does that not violate the law of conservation of energy?
  49. S

    Radiation Pressure and Conservation of Momentum

    How do you account for the conservation of momentum for a photon? Specifically, if you have light traveling in a medium where the refractive index is not constant. For example, a graded index multi mode fiber optic. So here is another diagram to help articulate my question. Inside this graded...
  50. Bunny-chan

    Conservation of the string length in pulleys

    Homework Statement This is a common massless string and pulleys problem. I'd just like to understand why, according to the solution, l_2 + 2l_1 = constant. It doesn't seem to me that two times the l_1 length is equivalent to l_2. Can somebody explain? Homework EquationsThe Attempt at a Solution
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