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. amandela

    Rolling Motion (Stone Gets Stuck in a Tire Going Forward)

    So I thought the stone would initially experience acceleration in the backward (leftward) direction then continually accelerate in the inward direction of the tire (i.e. upward then rightward then downward then leftward, etc.) as the tire moves forward. But the answer is immediately upward...
  2. pedrovisk

    Thermodynamics and harmonic motion

    TL;DR Summary: Problem said that the ball moves in a harmonic motion and asked to prove it. The process is adiabatic Problem said that the ball moves in a harmonic motion and asked to prove it. The process is adiabatic. I did the development, but at certain point I'm having a problem. The...
  3. Ineedhelpwithphysics

    Sign of Work (Negative or Positive)

    Im confused I did 850*9.8*14.7 = 1.2x10^5 Why is it not negative since the force is opposite to the motion?
  4. C

    Physics 1 Parabolic Motion Question Confusion

    Problem: A small forest animal jumps with an initial speed of v0 = 15.0m/s and travels to a maximum height of 2.160m. What horizontal distance would the animal travel if the launch angle is i) 45.0 degrees or ii) 42.0 degrees? Correct Answer: i) 24.95m ii) 25.02m My professor solved this by...
  5. Ineedhelpwithphysics

    Two dimensional motion problem (kicking a soccer ball into the goal)

    I did this too fast idk if I'm wrong So for the x component use the formula d = rt / delta x = v*t 26 = vcos(theta) y component use the displacement formula 19.6 = vsin(theta) tan^-1(19.6/26) = 36.5 degrees the answer key says 20.2 degrees idk whats wrong
  6. robotkid786

    B Is perpetual motion a forbidden topic in the scientific community?

    I've only just clocked this to be the case. I asked chat gpt and the say big bang has a lot of merit apparently
  7. Q

    Motion of Sphere Rolling Down Rotating Cone

    I am trying to understand the motion of the sphere in the image above, and I am a bit confused about the motion. How does the ball move down the cone? Will the rotation of the cone cause the ball to rotate with it, and which direction would the static friction be in? What does the path the ball...
  8. nrsakinh

    Need a real life example where a partial derivative is used in motion

    my group is preferring the ue of partial derivative to find the acceleration of a car or the projectile motion of something being launched
  9. Jolene

    Circular motion of a rollercoaster car on a loop-the-loop

    Can someone please check if I got the correct answer. Thank you! I got: Fy= N + Fg = mac N + mg = mv^2/r g = v^2/r r = v^2/g r = (48.61)^2/9.8 r =...
  10. S

    B Launch of a rocket - its initial displacement and velocity

    so then when we model the velocity of the motion of a rocket (e.g., in a mathematics report), is it reasonable to assume that the initial velocity equals zero? I also apologise for my lack of information if I made a huge mistake in my question 🙏🏻
  11. James1019

    Projectile motion only provided acceleration diatance

    TL;DR Summary: Find initial vertically upward speed of the ball Find horizontal speed of the speed Find angle How to: Find initial vertically upward speed of the ball Find horizontal speed of the speed Find anglei try to solve it but it didn't work
  12. James1019

    Projectile motion when only given distance and acceleration

    TL;DR Summary: Find horizontal velocity? I have no idea how to solve the problem, the question only provide distance 16cm(h),3.6cm(v) and acceleration = 0
  13. K

    Finding value of g given a motion map

    I tried using all equations of motion but couldn't get the correct answer. Any hint would greatly help. I've tried doing this for two days now!
  14. F

    Adjustable Hand Stroboscope, how to use?

    What kind of lab activity would you use an Adjustable Hand Stroboscope for? https://prolabscientific.com/Education-supplies/Physics/Force-and-motion/Stroboscopes/Hand-Stroboscope-Adjustable.html Would it purely be a qualitative activity? I can't imagine you can do anything really quantitative...
  15. MatinSAR

    In a constant acceleration motion, Is it possible to have constant speed?

    I think it's not possible. In 3D for constant acceleration we have : ##\vec v = \vec v_0 + \vec a t## It's a line in 3 dimension so velocity's magnitude(speed) is changing with time. I appreciate any better idea.
  16. P

    Help with question on motion: Avoiding a rear-end collision

    The question : A car and a truck are both traveling with a constant speed of 20 m/s. The car is 10 m behind the truck. The truck driver suddenly applies his brakes, causing the truck to slow to a stop at the constant rate of 2 m/s2. Two seconds later, the driver of the car applies their brakes...
  17. hyksos

    I Observation of the effect of gravity on the motion of antimatter

    The Alpha Experiment at CERN has finally produced a paper on whether antimatter falls towards the earth under gravity. The research confirms that antimatter acts identically to regular matter in regards to gravity. Observation of the effect of gravity on the motion of antimatter. Anderson...
  18. Lotto

    How many discs will slide off the board as it decelerates?

    I don't undertand the equation. It is Newtons's second law of motion, so it decribes a force that acts on a single disc relative to the ground. So when the force is proportional to velocity, shouldn't it be ##-bv##? Because the dics's velocity is ##v## relative to the ground. Relative to the...
  19. N

    I Newton's Second Law - variable mass case

    Dear Experts. In a problem where we need to calculate the acceleration of a satellite in a force free space which sweeps and collects interplanetary dust and a certain rate (dm/dt), I believe that the equation F = m(dv/dt) + v(dm/dt) can be used, by putting F=0 and substituting the function...
  20. Lil123

    Solve Disk & Coil Spring Motion: Get Amplitude Help

    I was able to solve part 1 but I am not not getting how to find new amplitude of the motion . Please help me
  21. MatinSAR

    Analyse motion of an oscillator: x(t)=0.2cos(12*pi*t)

    Hello. I have tried to solve it using x-t Graph. We know that period of this function is ##T=\frac {1}{6}s##. Then I've used ##x(t)=0## to find the times in which the oscillator is at ##x=0##: ##t=\frac {k}{12} + \frac {1}{24}## for ## k \in Z.## Now I can draw x-t graph. We should check time...
  22. D

    Translating reciprocating motion into a 45 degree rotation

    I'm trying to design a mechanism to translate reciprocating motion into a 45 degree rotation. Here's the idea: A pin will push against the part marked in red, causing part of the desired rotation. Then, when the pin is pulled back, its interaction with the blue part will complete a 45 degree...
  23. Xiothus

    Solve First Year Harmonic Motion Problem: Cylinder Rolling

    Thank you guys for taking the time to read this - I'm decently struggling with first year and need some tips on how to properly conceptualize problems and learn what the right approach is on certain problems. Have a wonderful day, again thank you for checking this post out!
  24. ARoyC

    Total Force on a Point Charge in Motion

    As the observer is moving, there will be a magnetic force. Electric Field of the Rod = λ/2πεr r̂ Electric Force on the Point Charge = qλ/2πεr r̂ Magnetic Force on the Point Charge = q(vxB) = qvB n̂ = qv(µI/2πr) n̂ = qv(µλv/2πr) n̂ = µqλv²/2πr n̂ Total Force = Electric Force + Magnetic Force
  25. Baela

    A Are equations of motion invariant under gauge transformations?

    We know that all actions are invariant under their gauge transformations. Are the equations of motion also invariant under the gauge transformations? If yes, can you show a mathematical proof (instead of just saying in words)?
  26. P

    I Rolling Motion direction of Velocity center of mass

    Hi I have come across something confusing in rolling motion. If an object moves with a positive V_cm meaning to the right its angular velocity will be clockwise or negative. The formula is V_cm=wR but for a positive V_cm you get a negative w as it moves clockwise if V_cm is to the right...
  27. LCSphysicist

    Majorana Fermions: Lagrangean and equations of motion

    $$i \gamma^{\mu} \partial_{\mu} \psi = m \psi_c \\ i \gamma^{\mu} \partial_{\mu} \psi_c = m \psi $$ Where ##\psi_c = C \gamma^0 \psi^*## Show that the above equations can be obtained from the followong lagrangian $$ L = \overline{\psi} i \gamma^{\mu} \partial_{\mu} \psi - \frac{1}{2} m \left...
  28. F

    Tusi discovering laws of planetary motion before Kepler?

    I was reading about the Tusi couple and read it "as a solution for the latitudinal motion of the inferior planets, and later used extensively as a substitute for the equant". Since the Tusi couple is related to plotting out an ellipse, did Nasir al-Din al-Tusi already discover the laws for...
  29. A

    Circular Motion: A coin on a rotating disk

    I believe I've solved this problem, however, I got through it pretty quickly and since it's the last problem on the assignment, I feel that I may have had an oversight. For part a, I got: fs=md(α^2)(t^2) and for part b, I got: ω=Sqrt((µs*g)/d) Could someone confirm my answers? I've attached a...
  30. A

    Circular Motion - Newton's Second Law: Bead on a Rotating Hoop

    For whatever reason, I'm having a hard time conceptualizing this problem. I understand that the tangential components of all forces involved need to cancel out in order for the bead to be stationary. I also understand that there is a mgsinθ in the negative θ-hat direction. What I don't...
  31. A

    B The synchronization of clocks and the relativity of motion

    In his thought experiment on the relativity of simultaneity, Einstein synchronizes two clocks A and B (at either end of a rod) to the clock C in a stationary frame, while A and B (the rod) is moving relative to C. The equations Einstein finishes with demonstrate how observers moving with A and...
  32. jed1408

    I Can angular motion exist outside of a gravity field?

    I can't find the answer anywhere here's my question. can a centrifuge exist outside a field of gravity. More specifically, in a theoretical void of nothing without stars in view or any point of reference for comparison how could motion like spinning or acceleration exist?
  33. A

    I Is it possible, that one physics law is "Everything is in motion?"

    Is it possible, that one physics law is "Everything is in motion?" (since zero doesnt belong to nature)...if so, does that implies that black holes move?
  34. C

    I On whether the motion of a Foucault pendulum bob is comparable to ballistics

    A recurring question is: while the motion of a polar Foucault pendulum is fairly straightforward, the case of a non-polar Foucault pendulum is quite difficult to visualize. In 2020, on physics stackexchange someone submitted that question and I contributed an answer. In a comment to another...
  35. strangerep

    QM Eigenstates and the Notion of Motion

    I'll risk a quick off-topic answer here, since I think it's straightforward QM, not vague "interpretation" stuff. :oldbiggrin: In QM (e.g., Ballentine p81), for a free particle, ##H = \frac12 \, M\, V\cdot V + E_0##. So in the ground state ##|E_0\rangle## we have ##H|E_0\rangle = E_0...
  36. V

    How to prove that motion is periodic but not simple harmonic?

    TL;DR Summary: Prove that a sum of trigonometric ratios is periodic but not not simple harmonic. We need to prove that ##x = sin{\omega t} + sin{2\omega t} + sin{4\omega t}## where ##x## is the displacement from the equilibrium position at time ##t##. I can see that each term is a SHM, but...
  37. A

    Friction, Mass and Acceleration: Analyzing Block Motion

    The block starts to slide if friction can no longer hold the block. F=u*n and F=(m1+m2)a so: (m1+m2)a=uN=>am1+am2=uN=>am2=(uN)/(am1) So:am2=(uN)/(am1) is the force. The answer is F=(u*m1g(m1+m2))/m2 I do not see how the acceleration terms are canceled. Is my answer equivalent to this?
  38. C

    Angle of acceleration in non-uniform circular motion

    For (c), Solution is Can someone please explain how they calculated that angle? I thought they would do ##arc\tan (\frac {32}{3.35})## Many thanks!
  39. themethetion

    Projectile Motion Using Vectors

    TL;DR Summary: Using vector functions how can I find the minimum average velocity (something greater than 11.86m/s) of a ball if the launch angle is unknown and if I have a point that the object must travel through (11.86, 3.47)? In my assignment, I developed a function for a lob shot...
  40. Sihas N

    A complicated problem of motion on rough surfaces

    I couldn't draw the motion after the collision, since the whole angular displacement of the plane got me confused.
  41. A

    I Is Brownian motion a purely classical phenomenon or is it also quantm?

    A water molecule is as tiny as 0.3 Angstrom. I would expect that quantum effects play a role. I'm wondering if its Brownian motion in a fluid is determined only by classical thermodynamics or if its collisional processes must take into account also quantum scatterings or other effects like...
  42. M

    Electromagnet Polarity Switching for Reversed Motion

    I am trying to understand the differences in design between a traditional solenoid with a ferrous plunger vs linear motors that use either induction or permanent magnets. From my understanding, a traditional solenoid, whether DC or AC, cannot fire in both directions with polarity switching since...
  43. E

    I Solving Spherically Symmetric Static Star Equations of Motion

    Hi guys, I can't seem to be able to get to $$ (\rho + p) \frac {d\Phi} {dr} = - \frac {dp} {dr} $$ from $$T^{\alpha\beta}_{\,\,\,\,;\beta} = 0$$ the only one of these 4 equations (in the case of a spherically symmetric static star) that does not identically vanish is that for ##\alpha=r##...
  44. Philip551

    Solving a Motion Problem with Work-Energy Theorem

    I have been trying to solve the following problem: Point-like object at (0,0) starts moving from rest along the path y = 2x2-4x until point A(3,6). This formula gives the total force applied on the object: F = 10xy i + 15 j. a) Find the work done by F along the path, b) Find the speed of the...
  45. DioMiner

    Why does this not work? Projectile Motion problem for Dynamics Class

    TL;DR Summary: I want to mainly figure out where in the problem solving I went wrong. I understand the correct answer (since I looked it up), but to me, it does not make any sense. I am honestly stumped at this point. Online solutions say that my equation y = 0.5774x-0.003354x^2 should...
  46. Z

    Solving for Simple Harmonic Motion: A Picture Problem

    Here is a picture of the problem It is not clear to me how to really prove that the equation for ##\theta(t)## is simple harmonic motion, and what the period of this motion is.
  47. N

    Is the Instantaneous Circle Proven When Centripetal Force is Removed?

    Can someone show that the instantaneous circle is indeed given by when the centripetal force is removed? This can be found at https://www.vedantu.com/iit-jee/circular-motion
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