Mechanics Definition and 999 Threads

Mechanics (Greek: μηχανική) is the area of physics concerned with the motions of physical objects, more specifically the relationships among force, matter, and motion. Forces applied to objects result in displacements, or changes of an object's position relative to its environment.
This branch of physics has its origins in Ancient Greece with the writings of Aristotle and Archimedes (see History of classical mechanics and Timeline of classical mechanics). During the early modern period, scientists such as Galileo, Kepler, and Newton laid the foundation for what is now known as classical mechanics.
It is a branch of classical physics that deals with particles that are either at rest or are moving with velocities significantly less than the speed of light.
It can also be defined as a branch of science which deals with the motion of and forces on bodies not in the quantum realm. The field is today less widely understood in terms of quantum theory.

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  1. S

    MHB Friction Mechanics: Solving for Block's Speed at Point A

    A wooden block of mass 3.5kg is sliding up a rough slope and passes a point A with speed 20m/s. The slope is at 29 degree to the horizontal. The block comes to rest 25m up the slope. Find its speed as it passes point A on the way down. I calculated coefficient of friction = 0.554. U=20m/s v= 0...
  2. S

    MHB Solving Friction Problem: Mass 5kg Trolley, 25° Slope, Coefficient 0.4

    A trolley of mass 5 kg is rolling up a rough slope, which is at an angle of 25 degree to the horizontal. The coefficient of friction between the trolley and the slope is 0.4. It passes a point A with speed 12m/s. Find its speed when it passes A on its way back down the slope. So I did F=m×a...
  3. heslaheim

    I Some questions in "Introduction to quantum mechanics"

    A certain field has a singularity at the origin, and the divergence of its curl is zero at any point outside the origin, but surface integral of the curl is not zero in the area of any closed surface containing the origin. So how should the Stokes theorem related to this field be expressed at...
  4. J

    Orbital mechanics: is ballistic capture possible without acceleration?

    All spacecraft that have been put into orbit around other planets have required engines to decelerate them and inject them into their orbits. So-called "ballistic capture", from what I've read, always seems to call for at least a minimum application of force to change the trajectory; I get...
  5. Feroyn

    Building a motorcycle, need classical mechanics help

    Hi! I am an engineering graduate that took my bachelor's degree in Mechanical Engineering much too long ago, but I have forgotten a lot of the classical mechanics/mechanics of materials theory that I had learned many years ago. I am building a motorcycle right now, and I want to calculate the...
  6. M

    B Description of isolated macroscopic systems in quantum mechanics

    If we prepare a macroscopic system (something like Shrodinger's cat) in a known quantum-mechanical state and we let it evolve for a very long time completely isolated, for what I understand the position of all it's particles will become more and more spread in space. But if the evolution of the...
  7. S

    MHB Mass 50kg Box Slows to Halt on Friction: 14.5m Distance

    A box of mass 50 kg is slowing down from 10 m/s on a rough horizontal ground. The coefficient of friction between the box and the ground is 0.3. To start with, the box is being slowed by a string providing a tension of 25N horizontally. Then the string breaks and the box comes to a halt under...
  8. S

    MHB Friction: Snooker Ball Mass & Speed Calculation

    A snooker ball of mass 0.4kg is struck towards a cushion from 0.8m away with speed 3m/s. The surface of the snooker table has a coefficient of friction of 0.3. When the ball bounces from the cushion its speed is reduced by 20%. Find how far from the cushion it stops.
  9. S

    MHB Mechanics: Friction - 200kg Bag Winched up 10m Slope at 6°

    A bag of sand of mass 200kg is being winched up a slope of length 10m which is at an angle of 6 degree to the horizontal. The slope is rough and the coefficient of friction is 0.4. The winch provides a force of 1000N parallel to the slope. At the bottom of the slope the bag is moving at 2 m/s...
  10. Soyuz42

    Work Done by Elevator Cable in Sample Problem 7-6

    As stated, part (a) says that the work done by the gravitational force ##\vec{F_g}## is 59 kJ. If ##W_T## is the work done by the elevator cable during the 12 m fall, then using the work-kinetic energy theorem, \begin{align*} K_f -K_i &= W_g + W_T\\ \frac12m({v_f}^2 - {v_i}^2) &= 59000 + W_T\\...
  11. S

    MHB Mechanics: Friction - Wheelbarrow Mass 8kg, Coeff. 0.6, Force 50N, Angle 30°

    A gardener is pulling a wheelbarrow of mass 8kg from rest along rough horizontal ground. The coefficient of friction between the wheelbarrow and the ground is 0.6. The gardener provides a force of 50N at an angle of 30 degree above the horizontal as shown in the diagram. a) Find the...
  12. S

    MHB Coefficient of Friction: Finding in a Factory

    In a factory, a machine picks up a box by clamping it on both sides. The box of mass 4kg is held clamped on both sides by identical clamps with the contacts horizontal. The machine provides a contact force of 50N with each clamp. Find the minimum coefficient of friction between each clamp and...
  13. S

    MHB Boy Exerts Force on 6kg Chair to Prevent Slipping

    A chair of mass 6kg is at rest on a rough horizontal floor with coefficient of friction 0.35. It is pulled horizontally by a force of 25N. A boy pushes down on the chair so that the chair is on the point of slipping but remains at rest. Find the force that the boy exerts on the chair.
  14. S

    MHB Find Magnitude of Total Contact Force on 20kg Box in 3 Cases

    A box of mass 20 kg is at rest on a rough horizontal ground. Find the magnitude of the total contact force in each of the cases. a) The box is pulled horizontally to the right by a force of 40N b) the box is pushed to the left by a force of 50N at 15 degree above the horizontal . c) the box is...
  15. P

    I Fictitious forces and their associated energies

    I understand the idea of a fictitious force. What I am confused about is the energy/potential associated with it. For example, if a cylinder of water is rotating, there apparently exists this centrifugal potential energy, which is obtained by integrating mrw^2 dr. Why is it that the...
  16. andrewkirk

    Troubleshooting a Frozen Far Roller on a Marcato Atlas 150 Pasta Machine

    This is a not very physics-related question, but I suppose fixing mechanical things involves a bit of physics, so I thought I might as well ask here. I have a Marcato Atlas 150 pasta machine that has stopped working. The crank won't turn because the rollers won't turn. The crank directly drives...
  17. A

    The Lagrange equations from mechanics

    I was having a doubt about the Lagrangian mechanics. Possible we can derive the lagranges equations of by extremisation principle of action, that is assume we already guess what is the lagrangian of the systeme. I say that minimisation procedure rely on assume a lagrangian, and then show it...
  18. P

    Moment of Inertia of a sphere about an axis

    I = 2/5M R^2 + Md^2 This is analagous to Earth's movement about the Sun. Is the moment of inertia of Earth about the centre of mass of the Earth Sun system = 2/5MR^2 + Md^2, where: M = Mass of earth, R = Radius of Earth, d = distance from Earth to centre of mass of earth-sun system.
  19. Y

    Rolling pendulum angular acceleration

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  20. J

    I Simulation of non-Hermitian quantum mechanics

    I noticed the research on NHQM in the following news release. New physics rules tested on quantum computer Published: 19.2.2021 Information for relevant paper is provided as follows. Quantum simulation of parity–time symmetry breaking with a superconducting quantum processor Shruti Dogra...
  21. D

    Confused about some basic mechanics principles (force , PE)

    Hi - i am confused about the following basic mechanics principles Consider a large cubic mass ( mass M ) on the ground with a small cubic mass ( mass m ) placed on top of it. The surface between the 2 masses is frictionless 1 - if a push (apply a force ) to the large cube does the upper...
  22. P

    If I pull a pulley, what is the tension in the string around it?

    I assumed that each of the masses attached to the string would be pulled with a force F, instead of F/2, which appears to be the correct value. Why is it F/2? I suspect the fact that the pulley is "weightless" has something to do with the F/2 value. What is it? Thank you.
  23. I

    Classical Reading Goldstein's Classical Mechanics as an Undergraduate

    We were prescribed Goldstein, Taylor and Marion/Thornton for our first course in analytical mechanics, and I'm about to finish up the course but I feel like I have not gotten a good physical, intuitive grasps of the concepts, so I've been trying to read the texts a bit more. Taylor and...
  24. Admiralibr123

    Sign of potential term in Lagrangian mechanics

    I have heard many times that it does not matter where you put the zero to calculate the potential energy and then ##L=T-V##. But mostly what we are doing is taking potential energy negative like in an atom for electron or a mass in gravitational field and then effectively adding it to kinetic...
  25. Sophrosyne

    A philosophy of quantum mechanics question

    There is an interpretation of quantum mechanics out there, and I was not sure if physicists take this seriously, or if it's one of those woo-woo popular misunderstandings of quantum mechanics. So I am posing it to our esteemed physicists here. It says that there can be all sorts of universes...
  26. P

    Is the Book Right? Examining Conservation of Momentum

    My proposed solution: When the student stops at the end, suppose the carriage is moving at speed u. 0 = (M+2m)u - m(v - u) ==> u = mv/ M+3m After jumping out, the total momentum of the Carriage + collector system is 0 - mu = -m^2v/ M+3m. By conservation of momentum for the Carriage +...
  27. P

    I Does the Normal contact force act through the centre of mass?

    Consider the following situation: You have 1 rectangular block lying on a table, and an identical block is placed above the block on the table. Now, this new block is constantly pushed to the right, right before it topples off. Consider the torque about an axis passing through the rightmost...
  28. P

    I Why is my derivation of the catenary wrong?

    Important note: I only derived the differential equation, I did not solve it. What I think caused the mistake: - the tangent approximation (tan(theta+dtheta) ~ tan theta + d theta
  29. P

    Why is static friction not considered in the work-energy theorem?

    My question is this: - Friction exists (for no slipping/pure rolling to occur) - Why is the work done against friction not accounted for in the conservation of energy equation? Thank you!
  30. P

    Conservation of energy in rotating bodies

    The conservation of energy equation is basically GPE is converted to KE of block and KE of cylinder. To get the correct answer, the KE of the cylinder is 1/2mv^2, where m is its mass and v is the velocity of its COM (which is the centre of cylinder). However, I viewed the cylinder as rotating...
  31. J

    I Origin of Probabilities in Quantum Mechanics?

    The non-normalized wavefunction of a general qubit is given by: $$|\psi\rangle=A|0\rangle+B|1\rangle.$$ The complex amplitudes ##A## and ##B## can be represented by two arrows in the complex plane: Now the wavefunction can be multiplied by any complex number ##R## without changing the...
  32. P

    Understanding basic statistical mechanics formulas

    Firstly, I would like to check my understanding of the first formula: Using velocity distribution = f(v), speed distribution = fs(v): fs(v) = f(vx)f(vy)f(vz)dxdydz, since dxdydz = 4pi*v^2*dv, fs(v) = 4piv^2f(v) The second formula is the confusing one: What does it mean? What is the...
  33. wrobel

    A Something about configuration manifolds in classical mechanics

    I think it could be interesting. Consider a mechanical system A circle of mass M can rotate about the vertical axis. The angle of rotation is coordinated by the angle ##\psi##. A bead of mass m>0 can slide along this circle. The position of the bead relative the circle is given by the angle...
  34. B

    Question concerning the mechanics of a magnet's attractive force

    Does a force exerted by a magnet change if we do not change the distance between a magnet and the body, but change the direction of the magnet (tilt)?
  35. cybernetichero

    Orbital mechanics question about Star Trek

    I'm watching the Next Generation episode Relics and Riker has just ordered the helm to "go into orbit above that point" which I took to mean geosynchronous orbit. No biggie except that the point is on the outer surface of a Dyson Sphere with a RADIUS of more than 1AU. So, assuming the sphere has...
  36. AuntyMatter

    A Shakespearean Guide to Quantum Mechanics

    When we think of the fathers of quantum mechanics we tend to think of Max Planck, Albert Einstein, Niels Bohr, Louis de Broglie, Max Born, Paul Dirac, Werner Heisenberg, Wolfgang Pauli, and Erwin Schrödinger. However I think I am in solid ground in suggesting that William Shakespeare was way...
  37. D

    I Shankar Quantum Mechanics, Chapter 5, Page 160-161

    For the case of general potential V(x), what does it mean when he says that there are always one more constraint than free parameters? At each interval, ψ and ψ' must be continuous, so that is 2 constraints at each interval, and I understand that there are 2 parameters of the wavefunction in...
  38. W

    Does any classical mechanics textbook solve Kepler's Problem?

    I have several* classical physics and mechanics texts, and none solve the Kepler problem (as far as I can tell), succinctly, solving the Kepler equation, M = E - e*sin(E), for E given M and e, or more generally determining the equations of motion for an orbiting object. In fact none even...
  39. T

    On the non-applicability of Newtonian mechanics

    Hello. The questions are: Why Newtonian mechanics is not applicable to quantum mechanics and more natural phenomena in gravity? So, we needed general relativity which offers a metric theory about gravity and applies to more phenomena in nature, but how is this explained that special and general...
  40. J

    I Quantum mechanics supports solipsism?

    There is a lot of information on the Internet that quantum physics supports solipsism and that physicists believe in solipsism. I only trust this forum and the people who are here, so I want to ask you: 1. Is it true that quantum physics says solipsism is true? If this is true, then only one...
  41. binbagsss

    Drop out of PhD in fluid mechanics and switch to Mres in mathematical physics?

    A post doc in an area that differs from my PhD? I am currently doing a PhD in fluid mechanics but want to do mathematical physics tbh. In another thread I got an answer about a user who had done a PhD in accelerator physics and went to do a post-doc in condensed matter, vice versa even, but in...
  42. D

    Prerequisite mathematics for intermediate mechanics?

    I will be taking intermediate mechanics next semester, and am a bit concerned about potential gaps in my mathematical knowledge. Long story short, I used to be a physics major, switched to electrical engineering, and then decided to double major after a semester in EE. The issue is that, as a...
  43. sergiokapone

    I What does motion mean in quantum mechanics?

    Consider the Schrödinger equation for a free particle: \begin{equation} -\frac{\hbar^2}{2m} \partial_i^2\psi = i\hbar\partial_t \psi. \end{equation} Let us be interested in the motion of a free particle in quantum mechanics. We say ok, we have a solution to the Schrödinger equation for a...
  44. jay_chay22

    Engineering Frame and Machine (engineering mechanics statics)

    I have problem on this question on how to draw free body diagram. Can you please show me on how to draw free body diagram on this question ? The calculation part I think I do not have a problem with it. Thank you in advance ! I am really struggle with this question.
  45. duchuy

    Point mechanics -- Tension in a rope from a hanging mass

    Hi, I'm being asked to determine the tension of a rope only knowing that g = 9.8 m.s-2. I understand that in order to calculate tension, I would need to multiply mass with acceleration. But i don't understand how i would in this case. This is the question for reference. Thanks for your help...
  46. B

    The definition of generalised momentum

    Why, in lagrangian mechanics, do we calculate: ##\frac{d}{dt}\frac{\partial T}{\partial \dot{q}}## to get the (generalised) momentum change in time instead of ##\frac{d T}{dq}##? (T - kinetic energy; q - generalised coordinate; p - generalised momentum; for simplicity I assumed that no external...
  47. F

    A First Course in Graduate Quantum Mechanics Resources

    What are some resources that you would suggest for a first course in graduate quantum mechanics? This includes textbooks, online courses such as MIT OCW(includes homework/exams), and online lecture notes?
  48. Leo Liu

    Relativity Is it worth to read the chapters on relativity in K&K mechanics book?

    Hello. I have almost finished Kleppner's Newtonian mechanics book except the part discussing special relativity. I plan to read Purcell's EM book after finishing it. I've heard some people saying that Purcell presents some of the EM concepts in a relativistic way, so I am a bit worried that I...
  49. Someone_physics

    A Thought experiment in relativistic quantum mechanics?

    Background --- Consider the following thought experiment in the setting of relativistic quantum mechanics (not QFT). I have a particle in superposition of the position basis: H | \psi \rangle = E | \psi \rangle Now I suddenly turn on an interaction potential H_{int} localized at r_o =...
  50. C

    Intro Physics Best textbook for properties of matter and fluid mechanics

    I am a First Year Undergraduate Physics student. Which will be the best textbook for me to study properties of matter (Elasticity) and fluid mechanics? I prefer a better theoretical understanding.
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