What is Motion: Definition and 1000 Discussions

In physics, motion is the phenomenon in which an object changes its position over time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed, and time. The motion of a body is observed by attaching a frame of reference to an observer and measuring the change in position of the body relative to that frame with change in time. The branch of physics describing the motion of objects without reference to its cause is kinematics; the branch studying forces and their effect on motion is dynamics.
If an object is not changing relatively to a given frame of reference, the object is said to be at rest, motionless, immobile, stationary, or to have a constant or time-invariant position with reference to its surroundings. As there is no absolute frame of reference, absolute motion cannot be determined. Thus, everything in the universe can be considered to be in motion.Motion applies to various physical systems: to objects, bodies, matter particles, matter fields, radiation, radiation fields, radiation particles, curvature, and space-time. One can also speak of motion of images, shapes, and boundaries. So, the term motion, in general, signifies a continuous change in the positions or configuration of a physical system in space. For example, one can talk about the motion of a wave or about the motion of a quantum particle, where the configuration consists of probabilities of occupying specific positions.
The main quantity that measures the motion of a body is momentum. An object's momentum increases with the object's mass and with its velocity. The total momentum of all objects in an isolated system (one not affected by external forces) does not change with time, as described by the law of conservation of momentum. An object's motion, and thus its momentum, cannot change unless a force acts on the body.

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  1. alexm

    Motion of rotating rig, find the angle variation with control rod length

    Summary:: We have a rotating arm, offset from the centre of rotation by a certain length, which is controlled by varying the length of a control rod. Need the angle of the rotating arm in terms of length of the rod. The blue line is a fixed column structure. CE and BD form the rotational...
  2. LawH

    B Energy, Mass, Speed of Light: Can We Reach It?

    Hello everyone! Let's say that you were to attempt to go as fast as possible on a spaceship with the mass of an average car in an absolute perfect vacuum. What I am wondering is, that if you were to reach a certain speed, and stop applying energy to this imagined spaceship, would the spaceship...
  3. Erucibon

    Circular motion and g forces in rollercoaster

    I my attempt, I set the drop height to 20m and using conservation of energy, i calculated the speed at the bottom. Calculating centripetal acceleration, if the radius of the circle is less than 10m then the g force is greater than 5, if equal to 10m the velocity at the top is 0 and there is 0...
  4. MIN JIN

    Circular motion of a car on a banked road

    f=(m v^2)/r
  5. R

    Movement contraptions that inspired Newton's 2nd law of motion

    Besides gravity that always works perpendicular to Earth and thus pulls apples from apple trees towards the ground, there must have been some sort of mid 17th century human made contraption, that used a constant force, produced to move objects with or without wheels, in a direction parallel to...
  6. Alexanddros81

    Vector Mechanics — Double Gear Rolling on a Rack

    Hi! My first question: How does he get the equation ##\frac {x_A} {2πr_1} = -\frac {θ} {2π}## ?
  7. jamiebean

    Why Does Projectile Motion Involve Zero X-Component Acceleration?

    I intended to finish the question with the equation of linear motion with constant acceleration, but it didn't work out. And I have no idea about the t^3 and t^4 of the position. How can I find the x component of the acceleration at time 3.4 s ? Where is the acceleration rate?
  8. T

    Projectile Motion — How far from the gun does the bullet land?

    I don't know how to link the x-component and y-component together.
  9. F

    Slip stick motion and a glass harp (singing glasses)

    -
  10. bri_garcia11

    How can I draw a motion diagram?

    I attached an image
  11. simo22

    Finding motion where the acceleration depends on position and time

    I have computed that the acceleration in my problem is a(t) = -gj - k/m(|r(t)| - L_0) * r(t)/|r(t)| Where a(t) is the acceleration vector, g is the gravitational acceleration, j is the unit vector in y-direction, k is the spring constant, m is the mass, r(t) is the position vector, |r(t)| is...
  12. S

    Projectile motion on an inclined plane

    a. I tried to "rotate" the inclined plane so the surface of the inclined plane becomes horizontal h = Vi sin θi . t - 1/2 g cos ∅ t2 and when it falls to the plane, y = 0 so: 0 = Vi sin θi . t - 1/2 g cos ∅ t2 t = (2 Vi sin θi) / (g cos ∅) Is this correct?b. Particle hits the plane vertically...
  13. P

    Rotational Motion Problem with Varying Centripetal Force and Friction

    Hello, I'm stuck in this rotational motion problem (advanced high school level). Source: Problems in General Physics- IE Irodov My attempt(s): First I tried using work done by the moment of friction (mgkR) and equated it with change in KE. I got the answer as ## \frac{R (\omega_0)^2}{8 \pi...
  14. russ_watters

    Insights Why We Don’t Discuss Perpetual Motion Machines (PMM)

    Continue reading...
  15. PeterDonis

    A Puzzle Involving the Moon's Orbital Motion

    This is a puzzle involving the orbit of the Moon around the Earth, based on the well-known story of Newton observing a falling apple and wondering if the same force that made the apple fall could also explain the motion of the Moon. The story goes that Newton considered the following: the...
  16. H

    What is the inverse of the covariance operator in Brownian motion?

    in fact the answer is given in the book (written by philippe Martin). we have $$ (\tau_1| A^{-1} | \tau_2) = 2D \ min(\tau_1 ,\tau_2) = 2D(\tau_1 \theta (\tau_2 -\tau_1)+\tau_2 \theta (\tau_1 -\tau_2))$$ So $$-1/2D \frac{d^2}{d\tau_1^2} (\tau_1| A^{-1} | \tau_2) = \delta( \tau_1 - \tau_2) $$...
  17. R

    Elliptical motion: An object is moving at a constant speed?

    I am confused why the acceleration doesn't point to the center of the ellipse or one of the focus, since it moves in circular motion. Shouldn't the acceleration be just in the radial direction
  18. SianRR

    Motion in Electric and Magnetic Fields -- (Uni Level Dynamics)

    I've attached my attempt at a solution below, I thought integrating it would be the best way to go but I'm just getting so confused and could use some help. This isn't my first attempt at a solution either I've been working on this for just under two hours now.
  19. J

    Perpetual Motion Idea: Is It Possible?

    Hi all,Minimal math/physics background here, so bare with me. Imagine a smooth track or tube that tightly spirals downwards into smaller and smaller circles. Now imagine if a ball rolls down that spiral, gaining speed. At the bottom/end of the spiral the track/tube goes underneath the spiral...
  20. P

    Equation of Motion of a Particle acted on by a retarding force

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  21. Beelzedad

    How to know whether motion is simple harmonic motion or not?

    I am reading "Coulomb and the evolution of physics and engineering in eighteenth-century France". There it is said in page 152 para 1 that "Coulomb found that within a very wide range, the torsion device oscillated in SHM". My questions are: (1) By just looking at the time period of the...
  22. tanaygupta2000

    Motion involving drag force

    Since given F = -kdx/dt so I equated mx'' = -kx' which gave x(t) = A + B exp(-kt/m) hence v(t) = (-kB/m) exp(-kt/m) and using v(0) = u, v(t) = u exp(-kt/m) then I...
  23. M

    Derivation of the Equations of Motion for a System

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  24. L

    Projectile motion of a two-point rigid body

    I would like to patch some gaps in my physics background. For example, I've been trying to come up with the sollution to the following: I have a model rigid body made up of two mass points and a massless rod connecting them. I throw the body with initial velocity under some angle of elevation...
  25. JD_PM

    Get all possible constants of motion given an explicit Hamiltonian

    I do not understand the following sentence (particularly, the concept of extra symmetry): 'If all ##\alpha^i## are the same, then there is extra symmetry and corresponding constants of motion'. OK so let's find the Lagrangian; we know it has to have the form: $$L(q, \dot q) = T(q, \dot q) -...
  26. R

    Question about the Signs of Rotational Motion

    I got a confusion about the sings in the angular acceleration. When dealing with system of pulleys, how to define where is the positive and negative direction of the motion and will the choose of positive direction of angular acceleration will effect the positive direction of linear acceleration
  27. T

    Projectile Motion with Air Drag

    Tell me now if this question is posted in the wrong place. This isn't a homework problem per se, it's just a question I need answered and I'm not sure how to answer it. If there is any information missing, chances are I know it and forgot to post it, so please ask if something is missing. I...
  28. T

    Deriving Momentum From Newton's Second Law of Motion

    Hello everyone I was hoping someone could shed some light on the following:- I am trying to derive the equation of Momentum from Newton's 2nd Law. What I know is the following:- I don't know how to get from Force = Mass * Acceleration TO Momentum = Mass * Velocity. I have attempted to...
  29. J

    Motion of 2 masses connected by a rod to a pendulum

    I am not sure which other forces I should consider besides those 3. I cannot consider tensions due to the massless rod on the masses since those will not add up to zero.
  30. JD_PM

    Using Noether's theorem to get a constant of motion

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  31. T

    Simple Harmonic Motion Amplitude

    Using A = x0, B = v0/ω I get ω = 4π, A = 1, B = 1/4π then converting to phase/magnitude form \sqrt{A^{2} + B^{^{2}}} = \alpha \sqrt{1^{2} + \left ( \frac{1}{4\pi }\right )^{^{2}}} = \alpha = \frac{1}{4\pi }\sqrt{16\pi^{2} +1} However the answer in the back of the book has α = 1 Is...
  32. JD_PM

    Equation of motion of a simple pendulum

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  33. cemtu

    Classical Mechanics "variable mass" linear motion problem in one dimention.

    Please help please
  34. B

    Rotational motion: Number of revolutions before a flywheel comes to rest

    Hi there I have been having a go at this question and I'm uncertain if my answer to part b) is valid? The problem is when I plug this into the calculator I get 6.379... revs however this doesn't make sense to me. 2*pi is roughly 6.28 radians so doing 4.061... rads / 6.28 rads = 0.647 revs...
  35. B

    Rotational motion and finding the moment of inertia

    Here is the problem that I am finding difficult to answer I had tried using conservation of energy to do this question Where I know that the gravitational potential energy at the top of the slope equals to the sum of both the linear and rotational kinetic energy at the bottom of the slope...
  36. T

    Help with a problem about motion — bullet striking a block of wood

    I first plugged my given values into m1v1+m2v2=(m1+m2)vf. (0.002)(600)+(5)(0)=((0.0020)+(5))vf vf=0.24 m/s Next, I plugged my given values into F=ma. ((0.002)+(5))(9.8) F=49.02 N Next, I plugged my given values into Fdeltat=mdeltav. deltat=mdeltav/F ((0.002)+(5))(0.24)/(49.02)...
  37. spacepirat

    Engineering Sectional Lift/Moment coefficients w/ sinusoidal motion

    I cannot figure out how to even start this.
  38. JD_PM

    Deriving the Equation of Motion out of the Action

    Exercise statement: Given the action (note ##G_{ab}## is a symmetric matrix, i.e. ##G_{ba} = G_{ab}##): $$S = \int dt \Big( \sum_{ab} G_{ab} \dot q^a\dot q^b-V(q)\Big)$$ Show (using Euler Lagrange's equation) that the following equation holds: $$\ddot q^d +...
  39. Alexan

    Please can I get some help finding the function of motion

    Homework Statement:: find the function of motion Homework Equations:: none i could find the amplitude and the phase angle but i can't find the phase difference and the function of motion.
  40. F

    Horizontal Circular Motion With Lagrange

    In the situation described in the problem, the mass is moving on a horizontal circular path with constant velocity. Wouldn’t this make L and U both constant? Then the Lagrange equation would give 0 = 0, which isn’t what I’m looking for. Any help would be appreciated.
  41. nineteen

    What is the minimum velocity needed?

    I tried to solve this problem and this is what I could come through: When the object is moving, the force acting on object is the frictional force, so, it got to be μmg. So, F = ma and as F is μmg μmg = ma μg = a So, to find out the magnitude of the initial velocity v given to the smaller...
  42. N

    Relativistic motion of an electron in a uniform electric field

    dv/dt is the acceleration, so I thought I could find the acceleration from F = qE = ma = dp/dt. But this is a relativistic case, so the proper acceleration is a = F/mγ3, where v in the gamma is the v of the electron and F = eE. However, I'm not sure if this is correct, because the constant τ...
  43. JuanC97

    I Do 4-divergences affect the eqs of motion for nth order perturbed fields?

    Intuitively, I'd say that adding a 4-divergence to the Lagrangian should not affect the eqs of motion since the integral of that 4-divergence (of a vector that vanishes at ∞) can be rewritten as a surface term equal to zero, but... In some theories, the addition of a term that is equal to zero...
  44. Adesh

    Can a magnetic field ever cause a translation motion?

    Lorentz Law says that for a charged particle moving with a velocity v in a magnetic field B then the force on it is given by $$ \mathbf{F} = q (\mathbf{v} \times \mathbf{B}) $$ Now, if I say that particle’s velocity and the magnetic field are aligned then according to Lorentz Law there will be...
  45. R

    Projectile Motion : Work and Energy

    The problem is based on a projectile-spring launcher. A ball is loaded into a tube that pushes back a spring and is then launched. The ball was launched straight horizontally not at an angle. I'm trying to find the work done on the ball by the spring. The info I have: Displacement of spring =...
  46. jedimath

    Exercise about Constant Motion

    NOTE: Sorry for my english. I use Google Translate! Comparing the performance with a friend of mine who is passionate about physics (and he is studying it by himself) we came to the same conclusion. In other words, we have calculated the time taken by both riders to reach the finish line. From...
  47. E

    Some quick questions concerning uniform acceleration and linear motion

    Hello, I hope you are all having a great day ! I've got a physics test in a couple of days and I have some questions:1. In a calculation, if the acceleration is in m/s², I presume the speed also has to be in m/s and not in km/h ? 2. So with this graph (v with t), I have to find the total...
  48. P

    Clarifying Ambiguities in High School Physics Problems

    I tried using the equation E(k)=1/2mv^2 and isolating for v but no mass was given. Then, I tried W=fd but there is no distance given. I don't know how to solve this.
  49. Z

    I QM & Motion: Is There Consensus?

    Is there consensus on the stance of QM in regards whether motion is actually continuous or not?
  50. A

    Harmonic motion of four meter sticks

    inertia of center = [(1/12) m*L^2 + m(L/2)^2]*4 inertia of center = (4m*L^2)/ 3 inertia around pin = (4m*L^2)/ 3 + 4m(L/ 2^(1/2) )^2 inertia around pin = (10m*L^2)/ 3 inertia around pin = (10*0.1*1^2)/ 3 = 0.33 kg*m^2 d= 1/2^(1/2) = 0.707m (m*g*d/inertia)^1/2 = 2pi/period...
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