What is Mechanics: Definition and 999 Discussions

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. Clout

    Fluid mechanics - pump in a horizontal pipe connecting two pipes

    So when the velocity of v1 and v2 is 0 (because the tanks are much bigger), the bernoulli equation to dh is dh = (dp-dpl)/(rho*g) with dp = Phyd / V = 1000W / 0.01m³/s = 10^5 Pa and rho = 1000 kg/m³ So I am getting first without the pressure loss on the orifice dh = 10^5 Pa / (1000 kg/m³ *...
  2. K

    Structural mechanics: Distributed forces on a structure

    Problem Statement: What's your result of ##X_A##? I find mine is different from the standard answer. Relevant Equations: My answer for $$X_A =5 kN$$ Problem Statement: What's your result of ##X_A##? I find mine is different from the standard answer. Relevant Equations: My answer for $$X_A...
  3. T

    Graphene and Newtonian mechanics

    I am writing a paper for "Dynamics and statics" course. I am really interested in Graphene. I am not if this is a good topic for this specific course. Any suggestions? Thank you in advance
  4. O

    Clearing a wall with a golf shot

    Every trajectory follows a parabola if we neglect air resistance. So we can calculate the maximum distance in x direction s_max. Also we can determine the time it takes to hit the ground again t_max. If the ground is everywhere the same height, I can assume that at t_max/2 the height (s_y) is at...
  5. J

    Simple clarification regarding the sign convention for work

    Precursor : Sign conventions regarding Work by the system/on the system may even vary among Physics textbooks and among Chemistry textbooks and as a rule of thumb it is better to clearly mark out the convention used by the text being referred to specifically and remain consistent with it...
  6. A. Neumaier

    I Numerical simulations in Bohmian mechanics

    With respect to the following posts from a now closed thread, https://www.physicsforums.com/threads/copenhagen-restriction-on-knowledge-or-restriction-on-ontology.968982/post-6169047...
  7. tonnijames

    Simple mechanics question: will reading of the scale change?

    My reasoning is that 1)at initial condition, net force of stick on the beaker is equal to the weight of the weight minus the buoyant force applied by the water to the weight, which is the tension force in the string. The recorded weight should be equal to mass of beaker + water + net force of...
  8. bardia sepehrnia

    Time needed for a Force F to accelerate the crate to 2m/s? (Dynamics)

    So above is the question. The picture below is my attempt at the solution: However the answer at the back of the book suggest that T=1.929s
  9. A

    I Which operator for reflection in quantum mechanics?

    Hello, I know we have the parity operator for inversion in quantum mechanics and for rotations we have the exponentials of the angular momentum/spin operators. But what if I want to write the operator that represent a reflection for example just switching y to -y, the matrix in real space...
  10. M

    Fluid Mechanics: Momentum Equation- When to include p_atm in equation?

    So if we define point 1 at the entrance and point 2 at the exit, then we can write out Bernoulli's equation along a horizontal streamline as such: p_1 + \frac{1}{2}\rho v_{1}^2 = p_2 + \frac{1}{2}\rho v_{2}^2 = p_{atm} One question is: won't there be p_atm also contributing to the static...
  11. M

    Fluid Mechanics: Momentum Equation Propeller Question

    For this question, this is my working. The main issue is I cannot figure out where the factor of \frac{1}{2} comes from. So I consider a control volume right around the propeller (in the frame of reference of the propeller) and I apply R(-->) Force = Change in Momentum Flux F = \dot{m_{o}}...
  12. M

    Fluid Mechanics: Head Loss Question (Conceptual)

    I am not really worried about the numbers, but more about the simple concepts with head loss in these pipe flow questions. I want to confirm that head loss just means the change in static head, right? I have been advised that for a problem like this, it is nothing more than the conservation of...
  13. WhiteWolf98

    Fluid Mechanics: Flow rate required to achieve a constant height

    Some thoughts that I've had on the question are saying the volume flow rate (##Q##) in, must equal the volume flow rate out. If that's the case, then: ##Q_{in} = Q_{out}## ##A_1V_1=A_2V_2## But... no areas have been given. And height doesn't enter this equation at all. Then I thought it...
  14. L

    I Definition of a symmetry transformations in quantum mechanics

    By the Wigner theorem, symmetries transformations are implemented by operators ##\hat{U}## that are unitary or antiunitary. This is what is written in most books. But I have read somewhere that, to ##\hat{U}## represent a symmetrie, it's necessary that ##\hat{U}^{\dagger} \hat{H} \hat{U} =...
  15. B

    Bodies connected by a light inextensible string on an inclined plane

    Here is the question (Qu 9): Here is what I have attempted: assumed that the accelerations are equal, found a value for the acceleration, thus worked out the time taken for A to reach the bottom. then assumed that the tension becomes 0 once A hits the floor, and then worked out B's new...
  16. snoopies622

    What is the logic behind Lagrangian mechanics?

    I like using the Euler–Lagrange equations to solve simple mechanical systems, but I'm not perfectly clear on the theory behind it. Is it derived by assuming that action is minimized/stationary? Or does one define a system's Lagrangian according to what makes the Euler–Lagrange equations...
  17. Clara Chung

    Work check and advice on a statistical mechanics problem

    b) Consider P_j(n) as a macrostate of the system, Bosons: P_1(1) = P_2(1) = 1/2*1/2=1/4 ,P_1(2)=P_2(2)=1/2*1/2=1/4 Fermions: P_1(1)=P_2(1)=1 (Pauli exclusion principle), P_1(2)=P_2(2)=0 Different species: P_1(1)=P_2(1) = 2*1/2*1/2=1/2 (because there are two microstates with corresponding to...
  18. Clara Chung

    Statistical mechanics problem of a book shelf

    Equations that might be helpful: Attempt: a) (N_max)!/(n!*(N_max-n)!) i.e. N_max C n b) Total Z = sum n=0 to N_max [(N_max C n) e^(buN)] = (1+e^(bu))^N_max Individual Z = 1+e^(bu*1) = (1+e^(bu)) so individual Z^N_max = total Z c) Now, I use Z to represent the total Z, By equation...
  19. EEristavi

    Relation between Potential Field, Force, Kinetic Energy and Abs.Energy

    I understand that the work done is Change of Energy. W = ∫xixf F dx = ΔEThe force is gradient of potential energy F = -∇U (For conservative forces of course) from here, we can say that change of potential energy is W: ΔU = -W but also ΔU = -W = ΔE I'm little bit lost here.. Can you help me...
  20. Clara Chung

    Statistical mechanics problem about a paramagnet

    I don't know how to solve part c and d. Attempt: c) B_eff=B+e<M> Substitute T_c into the equation in part b, => (B_eff-B)/e = Nμ_B tanh(B_eff/(N*e*μ_B)) Then? Thank you.
  21. P

    I Lawrence Krauss: Quantum Mechanics is deterministic (video)

    I understand partly what he is saying, but can you discount the measurement effect as a feature of the world? Aren't measurement effects going on all the time between macroscopic and microscopic systems, making it in practice, at times, an indeterministic world? Or is he assuming that...
  22. Celso

    Show that the terminal speed of a falling spherical object ....

    To write ##v## as a function of time, I wrote the equation ##m\frac{dv}{dt} = c_{2}v^2 + c_{1}v - mg \implies \frac{mdv}{c_{2}v^2 + c_{1}v - mg} = dt## To solve this, I thought about partial fractions, but several factors of ##-c_{1} \pm \sqrt {c_{1}^2 +4c_{2}*mg}## would appear and they don't...
  23. A

    Courses Electromagnetism 1 vs. Quantum Mechanics 2

    Hi all, I am an undergraduate junior majoring in materials science who would like some advice with respect to which courses to take for the fall semester of my senior year. Some background: I am a materials science student and I intend to study spintronics and topological insulators for my...
  24. T

    Mechanics question (beginner level)

    I'm okay with the concept of resolving into two components. BUT, with re: to resolving perpendicular to the acceleration, I don't understand how 25cos80 comes into? Surely it should be included when I'm resolving in the direction of the acceleration?
  25. A

    Fluid Mechanics, Particle Size, Bouyouncy Force

    1. What should be the size of object/Particle (sphere) so that it should remain suspended (neither it should sink nor it should float)? container dimensions 30*25*25, density of fluid 0.9g/cm3 , density of particle 0.86g/cm3 , particle is coated with aluminium having density of 2.07g/cm3.(if...
  26. A

    Rigid body mechanics, solution seems incorrect?

    I've attached the problem and solution as picture. To my understanding, the gear E and the rod OB are taken together as the rotating rigid body. However, the equations of motion and (##∑F = macm##) are applied to the center of mass of the rod, G, rather than the center of mass of the rigid body...
  27. R

    Mechanics Problem from MEXT scholarship 2007

    <Moderator's note: User has been warned to show some effort.> 1. Homework Statement Here this is a problem that I get troubled from MEXT scholarship examination. And the problem is Homework Equations F = mg Fx = cosa Fy = sina The Attempt at a Solution Is anyone can help me to solve the...
  28. stevendaryl

    I Wallis' Formula and Quantum Mechanics

    Does anybody know what the connection is between Wallis' formula for ##\pi## and quantum mechanics? There was an article about it: https://www.eurekalert.org/pub_releases/2015-11/aiop-ndo110915.php but like all articles for the lay public, all the details were left out. Wallis' formula is...
  29. K

    Need help finding the restraining reaction force for a beam

    1. The illustrated structure is affected by a known couple, and try to figure out the restraining reaction force of the hinge A and hinge E. We should analyse ECD instead. Since arm CD is a two force members, so N(C) in in the direction where CD connects by these two points. The distance from...
  30. astrocytosis

    Volume integral over a gradient (quantum mechanics)

    Homework Statement 1) Calculate the density of states for a free particle in a three dimensional box of linear size L. 2) Show that ##\int f \nabla g \, d^3 x=-\int g \nabla f \, d^3 x## provided that ##lim_{r \rightarrow \inf} [f(x)g(x)]=0## 3) Calculate the integral ##\int...
  31. L

    I Symmetries in quantum mechanics and the change of operators

    When we make a symmetrie transformation in a quantum system, the state ##|\psi \rangle## change to ## |\psi' \rangle = U|\psi \rangle##, where ##U## is a unitary or antiunitary operator, and the operator ##A## change to ##A'##. If we require that the expections values of operators don't change...
  32. R

    Mechanics of a car turning left

    Imagine a carom shot in a perfect world. A ball travels diagonally from the lower left-hand corner towards the right cushion and bounces off to head towards the upper left-hand corner. The ball has X and Y momentum. On the collision, the cushion absorbs and then return all the -X momentum to...
  33. LordGfcd

    A fluid mechanics problem -- Shape of a falling water drop

    Homework Statement A drop of water fall towards the ground with initial mass [m][/0] and radius [r][/0] (assume the initial shape of that water drop is sphere). the air resistance is F=½.ρ.A.[v][/2].C (C is the drag coefficent, A is the area that the air contact with the water drop and ρ is the...
  34. A

    I Black hole orbital mechanics questions

    What are some of the challenges associated with calculating orbital parameters of objects around a black hole (I.e. Orbital velocity, period, semi major axis, kinetic energy). At what point can classical physics no longer provide accurate results?
  35. jehwig0107

    A question regarding energy and momentum conservation

    I have a problem in mechanics. On the wedge and block only the gravisational force (mg) is exerted (and there is no friction in this system). What is asked in the question is the final velocities of the wedge and the block (vB, vK). The velocity of the block is conserved when it reaches at the...
  36. cHaRLie Bi0NiC

    B Quantum entanglement mechanics

    I should clarify, I am a linux administrator by trade and I have no physics or scientific background outside of working at a medical institute, So if my ideas are off and seem wild and misguided, please forgive my ignorance, and while you are at it be grateful for a fresh perspective. (joke) So...
  37. Demirci Kawa

    B Does the brain use quantum mechanics?

    We need quantum physics for cognitive neuroscience ?
  38. T

    How come "terminal velocity" and "final velocity" are different?

    Homework Statement Someone shot the bullet perpendicular to the ground. And there is air resistance. Velocity of bullet is v^2 = Ae^(-2kx)-g/k upward v^2 = g/k-Be^(2kx) downward A,B is constant, g is a gravitational acceleration, k = c2/m , c2 is a resistance constant, m is a mass...
  39. P

    I Where to publicise some notes on quantum mechanics

    I've struggled to understand quantum mechanics for many years. I've recently written some notes on the subject that address some of the issues that I've found confusing and that I think might be helpful to others. The moderators on Physics Forums, quite reasonably, won't allow me to publicise...
  40. J

    I What is Stochastic Quantum Mechanics (in simple terms)?

    Could someone, in laymen's terms explain to me what stochastic mechanics is?
  41. Alexanddros81

    I want to understand this equation - Fluid Mechanics

    Hi all! I have started reading Fluid Mechanics at my own pace (no university study) and really I would like to grasp the ideas behind it. So I have Fluid Mechanics by Cengel - 4th edition. At page 45 the coefficient of compressibility or bulk modulus of elasticity (κ) is introduced. ##κ =...
  42. B

    Textbook for calculus of variations? Hamiltonian mechanics?

    I need to learn about Hamiltonian mechanics involving functional and functional derivative... Also, I need to learn about generalized real and imaginary Hamiltonian... I only learned the basics of Hamiltonian mechanics during undergrad and now those papers I read show very generalized version...
  43. Danielpom

    Newton's 2nd law with oscilations

    Homework Statement a car moving to the left with constent accelration. a ball is hanging from the ceiling held in 90 degrees to the ceiling until t=0, then it is realesed and start to swing. find the max angle. Homework Equations Newton's second law The Attempt at a Solution...
  44. Demystifier

    Insights 9 Reasons Quantum Mechanics is Incomplete - Comments

    Greg Bernhardt submitted a new blog post 9 Reasons Quantum Mechanics is Incomplete Continue reading the Original Blog Post.
  45. learn.steadfast

    I Interpretations of diffusion in Quantum Mechanics.

    Recently, I've been told I was wrong concerning the nature of stationary states and diffusion being related. Even though I pointed out to the people involved that I was merely paraphrasing Max Born, who was apparently quoting the same idea as Linus Pauling. No one has been able to tell me...
  46. WhiteWolf98

    Fluid Mechanics: Determining Elevation in a Piezometric Tube

    Homework Statement [/B] Homework Equations ##P=\rho gh## The Attempt at a Solution So this is the first time I'm doing fluid mechanics, and I'm trying my best to understand it. This was the first question, and truth to be told, I'm not very confident. I know what gauge pressure is: the...
  47. A. Neumaier

    A Initial-value problem for Bohmian mechanics

    Does Bohmian mechanics have a mathematically well-defined initial-value problem with unique solution for given initial data? The right hand side of the guiding equation has singularities at all configuration space positions where ##\psi## vanishes. Thus the particle dynamics breaks down. Thus...
  48. K

    Quantum The main source books for quantum mechanics?

    I would like to know which books are the main sources for the Quantum mechanics 1/2 courses, and the professors use them most during their courses? Thanks for you reply in advance.
  49. D

    Quantum Quantum mechanics Zettili 3rd Edition available yet?

    Hi. I really like this book (2nd edition) and was thinking of buying it. I have seen mention of a new edition , the 3rd edition but it seems to be unavailable to buy. Anyone know if the 3rd edition is out yet or soon ? Thanks
  50. I

    I A question about velocities in Bohmian mechanics

    Hi all, In 'Bohmian mechanics,' (BM) velocities are given by the 'guiding equation' as explained, for instance, in this article of the Stanford Encyclopedia of Philosophy https://plato.stanford.edu/entries/qm-bohm/#DefiEquaBohmMech These velocities can, in principle, be greater than c. This...
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