Motion Definition and 999 Threads

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. A

    Constant acceleration problem: Dog chasing a surprised cat

    Here I'm not worried about the solution as I got it. There are two ways I could come up with: Either finding the time it takes the cat to leap through the window, use that time to find what distance does the dog cross through the room Or: finding both times, for the dog and the cat to cross the...
  2. CRJ

    Circular motion and moment of inertia - circle loop

  3. T

    Engineering Time interval until a ball returns to its orign

    This is my solution below.
  4. theblazierbroom

    Deriving the particle's motion using numerical integration

    When I used differential equation techniques, I found the function of x and v to be a negative exponential function. However, based on the notes, I believe the problem wants me to use finite summations as the relevant equations above. This stumps me because the acceleration is dependent on the...
  5. Zayan

    I Why do objects follow a geodesic?

    Gravity is considered as a bending of spacetime due to massive objects. And hence other objects around the curvature follow a geodesic path. My question is, why do they follow the path? Can't they be stationary? What's the cause behind objects even moving in the first place? I sometimes hear the...
  6. bremenfallturm

    Absolute motion analysis of pulley-spring system

    Hello! I have this problem from an old exam I'm trying to solve. The problem is in Swedish so I've translated it: NOTE that I accidentaly wrote $$C\neq 1$$ in the picture below. The correct problem statement is above. But that part is not what I have problems with. The answer key says "if the...
  7. S

    Vertical circular motion

    So far I believe that speed changes during vertical circular motion, and its very hard to get uniform circular motion that is in the vertical plane. This is because there is a difference in vertical height between the bottom/top of the circle so at the top the object must have done work against...
  8. painter

    B Generating Energy from Molecular Motion

    This question really troubles me. Since we all know that the molecules are in perpetual random motion, why can't we make a perpetual motion machine by using molecular's always-moving energy?? I‘m a Grade 9 student and I'm unsure about this. :doh::doh::doh:
  9. T

    Engineering Determining how far a body will move up an inclined plane and the time to reach the highest point

    15cos25 - 0.25N = ma.
  10. H

    A Equations of Motion for Torsional Inverted Pendulum on a moving cart

    Hello I am trying to figure out the equations of motion for the following scenario: a mass m is held upright on by a massless rod mounted on a cart that is being pulled by a linear force. The caveat is that the rod is mounted on the cart via a torsional spring which causes a restorative torque...
  11. A

    Projectile Motion Problem Involving Initial Velocity and Gravity Only

    Ok, so to start, the easy part, the velocity in the horizontal x direction (vx): vx = 20m/(2.5s) = 8m/s So far so good, but then for the vertical y velocity (vy), my answer is different than the book. I use the equation for position in the y direction, set the y value to 0 (the 2.5s it takes...
  12. tellmesomething

    Circular motion doubt: Angular velocity vector for general planar motion about a point in the plane

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  13. chwala

    Find the initial velocity ##U##

    Now in determining the initial velocity; in my understanding, if ##s=1.8## then we consider the stone's motion from the top to the ground. Why not consider ##s=3.6##, the total distance traveled by stone from start point ##t=0##? Is it possible to model equations from this point? The stone...
  14. A

    B Terminology for motion in the solar system, ecliptic maybe?

    Just looking for terminology here. If an object moves through the solar system, what is the simplest terminology that relates to how the object moves through the solar system? What are the words for if an object moves towards the sun (radially inwards) away from the sun (radially outwards)...
  15. R

    I How Does a Polygon Topple Without Sliding or External Force?

    How does a polygon shaped body's toppling shifts from one edge to next adjacent edge when the object is already in motion without any sliding and no external force is applied ? Explain it with the case of hexagon or octagon both ways, with and without including CoM.
  16. hello478

    Arrow being fired to centre of target

    i solved it like this... s = ut + 1/2 at^2 t= 1.08 (from part a) u= 65 sin4.30 a= 9.81? or -9.81 the answer said -9.81 why? wouldn't acceleration change from -9.81 to +9.81 because it moves up then down??? its soo confusing...
  17. 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...
  18. pedrovisk

    Where Did I Go Wrong in Proving Harmonic Motion in an Adiabatic Process?

    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...
  19. 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?
  20. 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...
  21. 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
  22. 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
  23. ritzcrackers

    Maximize Your Swinging Ball Force with These Expert Tips

    idk
  24. 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...
  25. nrsakinh

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

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  26. Jolene

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

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  27. S

    B Launch of a rocket - its initial displacement and velocity

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  28. James1019

    Projectile motion only provided acceleration diatance

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  29. 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
  30. K

    Finding value of g given a motion map

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  31. F

    Adjustable Hand Stroboscope, how to use?

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  32. MatinSAR

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

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  33. 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...
  34. 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...
  35. 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...
  36. 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...
  37. 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
  38. 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...
  39. 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...
  40. Sh4dman

    Velocity-time graph from distance-time table

    Question: Answer:
  41. 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!
  42. 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
  43. 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)?
  44. 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...
  45. 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...
  46. 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...
  47. 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...
  48. feesicksman

    Newton’s laws of motion -- Does the 1st Law presuppose the 2nd Law?

    .
  49. 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...
  50. 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...
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