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. Hoophy

    Circular Motion With Constant Angular Acceleration

    Homework Statement Question: A 600 g steel block rotates on a steel table while attached to a 1.20 m-long hollow tube. Compressed air fed through the tube and ejected from a nozzle on the back of the block exerts a thrust force of 5.01 N perpendicular to the tube. The maximum tension the tube...
  2. Hoophy

    Uniform Circular Motion, Find the Tension

    IMPORTANT! TEXT IN GREEN HAS BEEN ADDED AND IS CORRECT TEXT IN RED HAS BEEN REMOVED AND IS INCORRECT 1. Homework Statement Question: An energetic father stands at the summit of a conical hill as he spins his 25 kg child around on a 5.7 kg cart with a 2.3-m-long rope. The sides of the hill are...
  3. CVRIV

    Help with a problem involving motion in two dimensions

    I attached an image with problem and the associated illustration. I don't know what the relevant equations are for this problem. Each and every time I read the problem I keep drawing a right triangle to represent the velocity components. The problem says the river is flowing east at 5km/h. I...
  4. T

    Circular Motion Application Question

    Homework Statement First problem: The speedometer in a car is driven by a cable connected to the shaft that turns the car's wheels. Will speedometer readings be more or less than actual speed when the car's whells are replaced with smaller ones? Second problem: Keeping in mind the concpet from...
  5. D

    Circular Motion Problem: Particle Velocity and Acceleration Calculation

    Homework Statement A particle A moves along a circle of radius ##R = 50 cm## so that its radius vector ##r## relative to the point O (Fig. 1.5) rotates with the constant angular velocity ω = 0.40 . Find the modulus of the velocity of the particle, and the modulus and direction of its total...
  6. P

    The Importance of Understanding Different Formulas in Uniform Circular Motion

    https://i.imgur.com/4nynNBg.png I cannot understand for the life of me why this problem doesn't just use T = 2πr/v to solve for the period to get T = 2π(Lsinβ)/v. Instead, it rearranges the formula for a(rad) = (4π^2R)/T^2 to solve for T, and arrives at a totally different answer, T =...
  7. ju456one

    Projectile Motion: Pitcher throwing a ball to a catcher

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  8. S

    Motion of masses connected by a string over a pulley

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  9. M

    Derive the equations of motion

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  10. Pushoam

    Using symmetry of action to find the constant of motion

    Homework Statement Homework EquationsThe Attempt at a Solution I need help in solving second part of this question. I put ## e^{i \alpha }\psi ## instead of ##\psi ## and got to see that the integrand doesn't change which means the given transformation is a symmetry of the given action. But...
  11. D

    1D Angular Motion with different velocity stages

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  12. sweet springs

    B Time Dilation and thermal motion

    [Mentors' note: This thread was split off from another thread about the cosmic ray muon measurements] The particle at rest in the moving ship is moving against the Earth. The particle at rest on the Earth is moving against the moving ship. A scientist in the moving ship measures the life time...
  13. K

    Baseball in the air 2D motion question

    Homework Statement A baseball is hit into the air, nearly vertically, with a speed of 27 m/s. When it comes down, the ballplayer catches it in his glove. Air resistance (drag) is actually fairly important for a baseball in flight, but for now let’s assume it is negligible. (a) How high does...
  14. S

    Converting a nonlinear eqn of motion to a state-space model

    Homework Statement equations above are descriptive of a system with two configuration variables, q1 and q2. inputs are tau1 and tau2. d and c values are given. the question is about conversion of above equations to a state-space equation where the state-variables are x1 = q1_dot, x2 = q1_2dot...
  15. W

    B The unusual motion of stars in galaxies

    Ive been lying in bed this morning wondering about the unusual motion of stars in galaxies.The whole disc rotating like a record at the same speed.Does it mean that the effects of gravity are simply altered by speed?Much like a wonder-wall.So the faster the speed of the object,or stars,the less...
  16. T

    Projectile motion, ideal angle

    Homework Statement A frog jumps at t=0s and follows a projectile motion. The maximum height he reaches is 0.45m. The air resistance can be neglected. a) What is the initial speed of the frog in y-direction and how long is the total time until he lands on the ground? b) At which degree should...
  17. doglover9754

    Why does water not follow the law of motion?

    So I was in the bus going to school. I sat in the back not directly underneath the emergency exit but more like behind it. Anyways, since it’s been raining consistently, the emergency exits sometimes leak. So I’m sitting down and my jacket sleeve gets wet with a drop from the emergency exit. I...
  18. G

    Modeling a mass hanging by a spring: motion in 3D time/freq domain

    Hello everyone, I am new here, and wondering if anyone would have some knowledge on a current problem I have been working on. I am trying to create time- and frequency domain 3D models of an object hanging using a spring from a fixed point within a shell. I am trying to figure out how the...
  19. F

    Intrinsic coordinates and an intrinsic description of motion

    Hello, For 2D motion, I understand that velocity, position and acceleration of a point object can be described using the fixed basis vector ##\hat {i}## and ##\hat {j}## and the rectangular coordinates ##x(t)## and ##y(t)## which which are functions of time ##t##. Another option is to use...
  20. T

    Simple harmonic motion equation

    Homework Statement Calculate the harmonic motion equation for the following case A=0.1m, t=0s x=0.05m, v(t=0)>0 a(t=0)= -0.8m/s^2 Homework Equations x(t)= +/-Acos/sin ( (2pi/T)/*t) The Attempt at a Solution [/B] A is given to be 0.1 so I simply place it into the equation. Now I have to...
  21. Abhishek11235

    Deriving the small-x approximation for an equation of motion

    Homework Statement The problem is taken from Morin's book on classical mechanics. I found out Lagrangian of motion. Now to solve, we need small angle and small x approximation. The small angle approximation is easy to treat. But how to solve small x approximation i.e how do I apply it...
  22. Abhishek11235

    Find Lagrangian: Morin's Classical Mechanics Q6.10

    Q)6.10 in Morin's Classical Mechanic. All that I have to do is find Lagrangian here. After that only simple motion. Finding Lagrangian: Choose the coordinate system at the centre of hoop as shown in 2nd attachment. Then,I found out Lagrangian of the system. Invoking E-L Equations to find the...
  23. opus

    Projectile motion problems with No horizontal acceleration

    For projectile motion problems, we say that the horizontal component of the ball's path has no acceleration. The vertical component does, which is due to gravity, but in projectile motion it is true that horizontal and vertical motion are independent of each other. My question is in regards to...
  24. opus

    Understanding the Symmetry of Motion in a Parabolic Trajectory

    Homework Statement You throw a ball straight upward with initial speed ##v_0##. How long does it take to return to your hand? Homework Equations ##v=v_0+at## ##x-x_0=v_0t+\frac{1}{2}at^2## The Attempt at a Solution My question is a general one that relates to the described solution. According...
  25. Leo Consoli

    Why Does Gravitational Potential Energy Seem Absent in Magnetic Field Motion?

    Homework Statement A particle of mass M, with charge Q is left at the point A. After reaching point P the particle is at the effect of a constant and uniform magnetic field of intensity B reaching point Q. Find H. Homework Equations P=mg Fm=qvB Ke=(mv^2)/2 U=mgH The Attempt at a Solution...
  26. T

    Describing the Motion of a String at the Antinodes

    Homework Statement How would you describe the motion of a string at two adjacent antinodes? Homework Equations N/A The Attempt at a Solution So would the antinodes not be moving since it's a standing wave? Or would they be moving in phase because they are propagating together?
  27. J

    MHB 2nd order differential equation - equation of motion

    Hi There is an example in my textbook worded as follows; A particle of mass 2kg moves along the positive x-axis under the action of a force directed towards the origin. At time t seconds, the displacement of P from O is x metres and P is moving away from O with a speed of v ms^-1. The force has...
  28. F

    Rigid body kinematic motion and rotation

    Hello everyone, A rigid body is a system whose points, pairwise, always keep a constant mutual distance. Let's say the body is in a certain configuration ##C_0## at time ##t_0## (which means that each point has a specific velocity and position relative to a fixed lab reference frame) and the...
  29. opus

    Motion through a circular path

    Homework Statement Making a turn, a jetliner flies 2.1 km on a circular path of radius 3.3 km. Through what angle does it turn? Express in 2 significant figures. Homework Equations Arc length = ##S=rθ## The Attempt at a Solution Please see the attached image. I've tried multiple different...
  30. opus

    Motion problem -- The plug and chug at the end

    Homework Statement A car and motorcycle are racing along a runway. The motorcycle first takes the lead because it's constant acceleration ##a_m=8.40~\left(\frac{m}{s}\right)^2## is greater than the car's constant acceleration ##a_c=5.60~\left(\frac{m}{s}\right)^2##. But it soon loses to the car...
  31. Abourque72

    Period of Motion from Equations of Motion

    I would like to preface this by saying that I solved the homework problem, but my professor gave me an added challenge of finding the period of the motion described in this problem. 1. Homework Statement The pendulum bob of mass m shown in the figure below is suspended by an in-extensible...
  32. Rodney-Believes

    I Theory behind how expansion moves mass but doesn't interfere with inertia?

    If expansion is moving objects away from each other in space, does that imply an interface of some sort between space and mass, a connection, or friction? If so, how is it that mass can drift through space and not eventually come to a stop? If moving space exerts a force on mass, why wouldn't...
  33. JD_PM

    Dimensional analysis of an equation of motion

    Homework Statement The evolution of the density in a system of attractive spheres can be described by the following dynamic equation. $$\frac{\partial}{\partial t} \rho (r,t) = D_o [\nabla^2 \rho (r,t) + \beta \nabla \rho (r,t) \int dr' [\nabla V (|r-r'|)] \rho (r',t) g(r,r',t)]$$ a)...
  34. H

    Varying Gravity and Air Resistance in projectile motion

    Salutations, I have been trying to approach a case about projectile motion considering variation of gravity acceleration and air resistance: A spherical baseball with mass "m" is hit with inclination angle $\theta$ and launching velocity $v_0$, then, the wind has a drag force equals to ##F=kv##...
  35. W

    MHB What is the Magnitude of Force P to Keep a Block Stationary Against a Wall?

    A block of mass 3.00kg is pushed up against a wall by a force of P that makes a 50.0 degree angle with the horizontal (REFER TO PICTURE). The coefficient of static friction between the block and the wall is 0.250. Determine the possible values for the magnitude of P that allow the block to...
  36. K

    Rolling motion of Cylinders and Plank on a Slope

    Homework Statement A thin plank of mass M is placed centrally across two solid cylindrical rollers each of mass m, and the system is allowed to move freely from rest without slip down a slope of angle θ as shown in the figure below. (a) Derive expressions for the initial accelerations of the...
  37. S

    What is the Velocity of a Rotating Weight?

    Homework Statement A weight is suspended from a spring 50 cm long and stretches it by 1 cm. Take the other end of the spring in your hand and rotate the weight in a horizontal plane so that the spring is stretched by 10 cm. What is the velocity of the weight? (The force with which the stretched...
  38. Abdullah Wahid

    Perceived gravity in circular motion

    Is there any thing like perceived gravity in circular motion?? If I consider that it is in opposite direction to centripetal force, then both perceived gravity and centripetal should cancel each other and object should move in a straight line. Why does it nit happen?
  39. T

    Motion on a rough inclined plane

    Homework Statement A car is moving up a rough inclined plane/road of 10 degrees with a velocity of 10m/s. The coefficient of friction is equal to 0.5 and the mass of the car is 10kg. The car brakes. After what distance does the car stop? Homework Equations F=ma v^2=u^2+2as u= initial velocity...
  40. P

    Calculating Slingshot Projectile Motion - Finding Initial Velocity

    Homework Statement "The slingshot exerts 40 N for 0.25 s. If Red bird is released 5 meters above the ground, and kills the pig, how far away is the pig?" m = 0.75 kg; angle = 45 degrees Homework Equations x = (initial velocity in x-direction) * (time)[/B]The Attempt at a Solution In order to...
  41. S

    I Math of charts derrived from projectile motion equations

    Recently I was playing around with the idea of graphs of projectile motion and I started wondering what it would look like if someone were to graph every parabolic trajectory of a single initial velocity over all angles between o and 90 degrees above the horizontal. I decided to find out so in...
  42. Y

    Designing a Banked, Circular Highway Exit | Help with Homework

    Homework Statement The task is to design a highway. I did a similar project last year but I have completely forgotten and have no clue what to do. You have to design a banked, circular, clockwise highway exit. you knwo you have 5000 sq. meters. of land to build it on..you also know that the...
  43. N

    How to break up kinetic energy for circular motion?

    Homework Statement Homework Equations L = T-V For constant frequency tangential velocity is (radius)*(w) The Attempt at a Solution I need to find r(t) using the Langrangian L = T-V I just was not sure whether I am on the right track for calculating the total kinetic energy for the above...
  44. B

    Mathematica Equation of motion in Mathematica

    I have a question to a physical task in Mathematica. We have this equation of motion: For energy of masspoint there is the condition : I have to write a procedure that uses the law of the conservation of energy for the potential V(x) to calculate t(x_1) - t(x_0) when there are given two...
  45. A

    C 12B 2021 #23Analyzing Motion Graphs: Understanding Slopes and Acceleration

    Homework Statement [/B] picture 1: picture 2: Homework EquationsThe Attempt at a Solution For the first picture I was thinking answer B because at the start velocity increases, but as terminal velocity is hit the velocity doesn't increase as much.. why is it graph A? For the second...
  46. Bilal Rajab Abbasi

    Projectile motion problem, given the KE at the top of the parabolic arc

    Homework Statement Calculate the angle of Projection for which Kinetic Energy at the highest point of trajectory equal to one-fourth of its kinetic energy at point of projection? Homework Equations Range and height of Projectile equations The Attempt at a Solution [/B] I've made two...
  47. L

    Planetary Motion: Orbit Transfers, Hohmann transfer

    The thought of increasing a satellite's (for example) speed to allow it to transfer from a "higher energy" elliptical orbit to a "lower energy" circular orbit (in reference to the effective potential energy plot that arises after introducing the concept of an effective mass to simplify the...
  48. J

    Confused about a simple harmonic motion problem....

    Homework Statement A vertical block-spring system on Earth has a period of 6.0 s. What is the period of this same system on the moon where the acceleration due to gravity is roughly 1/6 that of earth? Homework Equations w = √(k/m) w = (2Pi)/T T = 2Pi*√(m/k)[/B] The Attempt at a Solution So...
  49. Dorian

    Position vs Time Graph: Simple Harmonic Motion

    Homework Statement [see attached photo] I seek specific help with (a) only. The answers to this question are provided in the back of the textbook, so I know the answers (I hope). Homework Equations ##x(t)=Acos(\omega t+\phi _{0}),## ##v_{x}(t)=-A\omega sin(\omega t+\phi...
  50. Cc518

    Object A is stationary while objects B and C are in motion.

    Homework Statement Object A is stationary while objects B and C are in motion. Forces from object A do 10 J of work on object B and –5 J of work on object C. Forces from the environment do 4 J of work on object B and 8 J of work on object C. Objects B and C do not interact. What are ΔKtot and...
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