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. N

    Atwood's with a cylinder - Rotational Motion

    I am confused about three things: (i) To prove that accelerations are same, in the book it is given: ##mg−T=ma_1## (for the block) ##mg−T=ma_2## (for the cylinder) ##(a_1 = a_2 = a)## And thus the accelerations should be same. I can see that the same forces are acting on the bodies and that...
  2. L

    B Friction and Newton's laws in car braking systems

    When tires lock, the tires exert a forward force on the ground and the ground exerts a reaction force (kinetic friction) on the tires in the opposite direction. But if the car brakes slowly, the tires are still rotating and so they exert a backward force on the ground, and the ground exerts a...
  3. nightsailor833

    How to solve this kind of problem? (Mechanics Theory)

  4. Islam Hassan

    I Lagrangian Mechanics, Continuous Particle Paths and QFT

    In the following thread: https://www.physicsforums.com/threads/particle-movement-in-quantum-mechanics.1054807/ the discussion established/confirmed that the matter of a particle’s continuity of movement in Quantum Mechanics QM is not a scientific question in QM, refer to PeroK post # 6...
  5. misu

    A chain suspended on a Pulley

  6. N

    Two bars connected by a spring on a floor with friction

    So I do realise that this problem involves energy, I still wrote equations for forces acting on each block. I will assume coefficient of friction to be ##μ## for convenience. For block 1: ##F - kx - μm_1g = m_1a## For block 2: ##kx= μm_2g## I then wrote an energy equation assuming a velocity...
  7. mathisrad

    Looking for good books explaining Lagrangian and Hamiltonian Mechanics

    TL;DR Summary: Need some sources for Lagrangian and Hamilton Mechanics. I was looking through some of my physics books, and in one chapter they mentioned Hamiltonian and Lagrangian Mechanics, I thought it seemed pretty useful and looked into it some more. I noticed that these mechanics were...
  8. daisy7777

    Engineering Solving for the Reaction Force by taking Moment about a Point

    For this problem, I took the moment about point B to 'get rid' of the tension force in the cables BA and BC. By doing this, I figured I could solve for the x and y components of the reaction force at D. From there, I could solve for the tension in BA and BC in the x and y and then solve for Dz...
  9. N

    A microwave oven of mass 13.0kg is pushed a distance 8.80m up a ramp

    For this one, am i supposed to use W = change in KE where i calculate work as ((F - friction - mgsintheta) times d), or am i supposed to do the change in -mgh plus Wfriction = change in KE (where if it is in this case, is the friction going to be a negative number?)
  10. yawmid

    Optimal roller distance for dynamometer

    I am currently building a dynamometer to measure the power consumption and rpm of a mars prototype. The plan is to place each wheel of the rover onto a pair of rollers but I am currently struggling with determining the optimal roller separation. If they're too far apart, the wheel might not...
  11. BvU

    Sell Bjorken and Drell

    Classics ! James D. Bjorken, Sidney D. Drell - Relativistic Quantum Mechanics (1964) James D. Bjorken, Sidney D. Drell - Relativistic Quantum Fields (1965) Sold as a pair (reasonable infraction on the 1 book/thread guideline) Mint condition
  12. J

    Quantum Identifying old quantum mechanics text book

    Hello everyone, I'm trying to recall the title and author of a quantum mechanics textbook I read many years ago, likely a couple of decades or more. My local library had what I thought was a very good quantum mechanics book, which I worked through during the summer holidays after completing my...
  13. M

    Quantum Mechanics Boundary conditions

    For this problem, The solution is, I have a doubt about Step number 3 about boundary conditions. Someone maybe be able to solve that doubt? Kind wishes
  14. R

    I To predict the nature of Normal Reaction in any mechanics set-up

    Is it true that in any mechanical set-up, it is possible to predict the nature of Normal Reaction ( magnitude, direction, etc. ) without solving through the dynamical equations of motion and constraints for the set-up as Normal Reaction is completely unknown? I mean is it true that we can...
  15. S

    Questions about information limits in the Universe

    For a hammer all problems are nails, and for a signal processing animal like me, it is all about information :cool: The laws of mechanics limit the info needed to describe/define motion. The limited number of finite sized stable elements, built using smaller number of particles, limit the...
  16. QuantumOscillatorIII

    How friction acts on a block moving down a slope moving side to side

    TL;DR Summary: How friction acts on a block moving down a slope moving side to side I found this problem, and I've also attached its solution. My question is, if the block wants to move down the slope, and also wants to move side to side and follow the movement of the plane - where does...
  17. Jovin Sanga

    Hello Physicists! I'm a new member

    I found Physics Forums via Google search. I'm a Tanzanian citizen pursuing a bachelor's degree in Physics (minor in Economics) at The Open University of Tanzania. I'm a first year undergrad. I'm glad to be a part of a huge community of like-minded people. I'm especially passionate about...
  18. Y

    B Feynman's lectures: Newton’s Laws of Dynamics

    https://www.feynmanlectures.caltech.edu/I_09.html
  19. Quantum55151

    I Mechanics of an inertial balance

    In the following diagram (from Taylor's Classical Mechanics), an inertial balance is shown. Intuitively, I totally understand that unequal masses would cause unequal accelerations and therefore rotational motion of the rod. However, how does one prove this mathematically? The first thing...
  20. Quantum55151

    Classical What are the best intermediate Newtonian mechanics textbooks?

    I am currently looking for a good textbook on Newtonian mechanics but am unable to find anything that suits my specific needs. I have already done an advanced high school mechanics course and would like to take a more sophisticated look at the subject over the summer, in preparation for a course...
  21. M

    QM time independent perturbation theory

    The lowest two energy level corrections (l=0, s_{z}=-1/2 and l=0, s_{z}=1/2) are easy to work out since the eigenvalues are not degenerate and the unperturbed energy levels also happen to be eigenstates of H'. However I have three degenerate energy levels for the third eigenvalue of the form...
  22. L

    Quantum Mechanics - Time dependent solution - x's and t's not mixed up

    Next, we assume a solution in this form: Which simplifies (according to my notes) to this: In the middle equation, we have factorised out the F(t). My question is why is it wavefunction(x,t) rather than wavefunction(x). I first thought it was a mistake in the notes, but it uses the same...
  23. D

    B How do physicists know if limits exist, things are integrable, etc?

    My last thread had too many questions, so I was told to make a new one. The question in this thread does not seem the same as the ones in the last thread, but I supposed that this is the root of my problems, so I started here. Also I wasn't sure whether to put this in the physics section or the...
  24. M

    Two masses connected by Pulley - Lagrangian problem

    For this problem, My solution to (a) is, We have constraint ##x + y = L##. There are many places we could define our (x,y) Cartesian coordinate system. However, the most easiest I think for the problem would be to attach a ##x^*## and ##y^*## coordinate system at the COM of ##m_1##. We define...
  25. W

    I Question about Cartesian Tensors

    I am not a mathematician but an Engineer-in-Training studying mechanics. That being said why does equation I-10 equal 1 when k equals i and 0 when k does not equal i?
  26. Elaren

    Quantum Better advanced Quantum Mechanics book than Sakurai?

    Sakurai's Modern Quantum Mechanics is 1/2 of a very good graduate textbook. Unfortunately Sakurai passed away midway through writing it, and it is very obvious exactly where it swapped from their writing to just using their notes. The back half of the book, while by no means bad, is notably less...
  27. B

    Force on a rotating wheel/disc

    TL;DR Summary: A force which stops a wheel/disc from rotating Hi! I made a problem myself inspired by a typical mechanics problem, where you have two equal forces acting on each end of a wheel/disc and a third one that is suppose to stop the wheel/dic from rotating. So let me get into the...
  28. Spathi

    Can quantum mechanics be combined with game theory?

    I suppose, anybody here knows about the Elitzur–Vaidman bomb tester and the counterfactual definiteness: https://en.wikipedia.org/wiki/Elitzur–Vaidman_bomb_tester https://en.wikipedia.org/wiki/Counterfactual_definiteness I have a question: can this experiment be performed at the level of...
  29. B

    Textbook 'The Physics of Waves': Reason to force us to consider complex solution for harmonic motion?

    TL;DR Summary: The reason to force us consider complex solution for harmonic motion. Reference textbook “The Physics of Waves” in MIT website: https://ocw.mit.edu/courses/8-03sc-physics-iii-vibrations-and-waves-fall-2016/resources/mit8_03scf16_textbook/ Chapter 1 - Section 1.3 (see attached...
  30. T

    IPHO classical mechanics: A mass falls on an exoplanet

    Attempt: I assume that the position of the mass ##M## after it is realised its position is given by the position vectors from the origin, ##\vec m = -m(t)~\hat m## if ##m(t) > 0## or equivalently ##\vec m = m(t)~\hat m## if ##m(t) < 0## Either one we can use for energy conservation (I am...
  31. D

    B Sign conventions in torque and non-uniform circular motion

    Sorry for the overly general title but my problem is regarding a specific problem: find the net force on the bob of a pendulum as a function of ##\theta##, the angle it makes with the vertical (assuming the observer is stationary with respect to point from which the string is hung and the...
  32. K

    Engineering Which is the strongest of these 3 beam cross sections?

    Added solutions. Check if there is a correct solution.
  33. Justina

    Enthusiast of Quantum mechanics

    Hi everyone I'm Justina. I'm excited in joining physics forums and I'm high school student who is interested in Quantum mechanics a lot .I used to spend lot of time on knowing Quantum mechanics and i learnt few little things. And this is my first time, joining an online community hope I will...
  34. barondress

    How can I maximise the exit velocity of an object catapulted up?

    n/a
  35. MatinSAR

    Statistical mechanics: particles in magnetic fields

    Let’s consider that the total energy of this system is represented as ##E=-2mB##. Question 1: how many microstates correspond to this energy level? We have ##2^4=16## microstates. ++++ Total magnetic moment: ##4m## Energy: ##-4mB## - - - - Total magnetic moment: ##-4m## Energy: ##4mB##...
  36. Sam Jelly

    2 Masses attached by a spring in the vertical axis

    I am trying to solve this problem without using energy conservation. How can I solve this using the 2 body system and center of mass. I know that in order for mass m at the bottom to be slightly off the ground the reaction force must be equal to zero. I don’t know if the reaction force before...
  37. G

    Force components for mass attached to two springs

    So at first I tried to express the potential energy as a function of x, y and z, but since I'm not quite sure about the geometry of the situation, I decided to separate out the potential energy into three components: ##V_x, V_y, V_z## (I'm pretty sure this is valid because in the partial...
  38. Sam Jelly

    Proving the gravitational force of a solid sphere using integration

    This is my attempt at the solution. x from the equation dF = GmdM/x^2 represents the distance between the circular plate’s center of mass and mass m.
  39. K

    Cantilevered and line-loaded steel beam

    I found the internal force Vxy 25 +6 =31kn. , bending moment Mmin -qb2/2 , M min- 14 kNm. delta =M/W I can't find Mmax and tau= V/As. So I need help to find Mmax and As wall area, how to find.
  40. lambdadandbda

    Can You Set Energy Conditions in Zwienbach Exercise 6.2?

    I can write $$\psi(x,t_0) =\frac{1}{\sqrt{2}}(e^{\frac{-iE_1}{\hbar}t_0}\psi_1(x) +e^{\frac{-iE_2}{\hbar}t_0}\psi_2(x))$$ for the second coefficient to be -1 i need ## -1=e^{-i\pi}=e^{\frac{-iE_2}{\hbar}t_0} ## so ##t_0=\frac{\pi\hbar}{E_2}## and the above equation becomes $$\psi(x,t_0)...
  41. G

    Finding slip-off angle for mass off of sphere?

    [Rewriting this as per the suggestions. Thanks once again.] I won't be using the Lagrangian because it was never explicitly stated that I have to so I'll just use conservation of energy. $$ T = \frac{1}{2}mv^2 = \frac{1}{2}m(R\dot{\theta})^2 = \frac{1}{2}mR^2\dot{\theta}^2 $$ $$ V = mgy =...
  42. Frabjous

    Quantum Constructing Quantum Mechanics by Duncan

    Anyone read these books and care to share their thoughts? https://www.amazon.com/Constructing-Quantum-Mechanics-Scaffold-1900-1923/dp/0198845472/?tag=pfamazon01-20 https://www.amazon.com/Constructing-Quantum-Mechanics-Arch-1923-1927/dp/0198883900/?tag=pfamazon01-20
  43. T

    Recommendation for a book on Hamiltonian Mechanics

    Homework Statement: Practical examples of Hamiltonian Mechanics sought Relevant Equations: Hamilton Jacobi Equations, MTW Hi, I'm currently a bit stuck on Box 24.2 in MTW. I really need to get a better understanding of Hamiltonian Mechanics to be able to work my way through this and I...
  44. Hennessy

    I Calculus Question within Lagrangian mechanics

    Hi all currently got a lagrangian function which i've found to be : \begin{equation}\mathcal{L}=\frac{1}{2}m(\dot{x}^2+\dot{y}^2+4x^2\dot{x}^2+4y^2\dot{y}^2+8xy\dot{x}\dot{y})- mg(x^2+y^2) \end{equation} Let us first calculate $$(\frac{\partial L}{\partial \dot{x}})$$ which leads us to...
  45. R

    Final velocity of the barbell dropped after a dead lift

    Eddie Hall is the current world record holder in the deadlift, a powerlifting maneuver in which a weighted barbell is lifted from the ground to waist height, then dropped. The figure below shows a side view of the initial and final positions of the deadlift. A side view of the initial position...
  46. kuruman

    Insights How to Solve a Multi-Atwood Machine Assembly

    Continue reading...
  47. C

    Calculate how much weight the crane could lift

    I think the first part is F = mxa? But given the jib is resting on a turntable at a certain distance, does that mean the longer and shorted ends experience different loads? Especially when the shorter end has a 16T counterweight? The second part, I have no idea how to calculate this nor the...
  48. GLD223

    Generalized coordinates and the Lagrangian

    So I think the mass can only move in two "coordinates" the axis of which the mass is connected to ##k_1## and the axis connecting it to ##k_2##. Therefore, the D.O.F is 2. I don't understand what it the meaning of "variables of integration" What does it mean? Apart from that, I attempted to...
  49. D

    I Why L=L（v^2) in inertial reference system?

    Why he said that beacause space's propertiy is the same in both direction, so L=L(v^2), or do I misunderstand him incorrectly? btw this conclusion appears in somewhere like page 5 and its about Galilean principle of relativity.
  50. TheePhysicsStudent

    Need help on some mechanics questions from a text book

    These are the questions I am failing to comprehend despite their very basic nature This is the wonderful support from the book explaining how to get the answer ! (It just gives you the answer no working out which is annoying) I
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