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. K

    Projectile Motion: stream of water

    Homework Statement (For this problem ignore the height of the firefighter) A firefighter, a distance (d) from a building, shoots a stream of water at an initial angle, above the horizontal, at initial speed (Vo). At what height (h) does the water strike the building? No values were given to...
  2. jaumzaum

    A PDF of random motion - similar to Browninan motion

    Hello guys, and sorry for my english in advance. I was presented some time ago with the following problem: Suppose there is a frog that jumps in any direction randomly, and all the jumps have size 1. What's the probability of, after 3 jumps, the frog be less than 1 unit from the origin. I...
  3. O

    Motion of a non-linear pendulum with air resistance

    Homework Statement I need to come up with an equation that would model the motion of a non-linear pendulum with air resistance. [/B]Homework Equations Fc=mgsintheta Fdrag=(1/2)p(v^2)CA The Attempt at a Solution I started with mgsintheta-(1/2)p(v^2)CA=ma After substituting v=r*omega and...
  4. thebosonbreaker

    B Is the lift generated by a hummingbird's wings an example of Newton's Third Law?

    Hello, I understand that Newton's laws of motion can explain how a hummingbird is able to hover in front of flowers. There is one question I have in particular, which is, Is the lift generated by the wings of the bird and its weight force an example of a pair of Newton's third law forces? They...
  5. J

    Help with a confusing free-fall motion physics problem?

    I'm taking physics for the first time, and I've been attempting the textbook problems, but I can't seem to get it. 1. West stands on the roof of a building, leans over the edge and drops a rock. Lindsay waits 1.25 s after West releases his rock and throws her own rock straight down at 28.0...
  6. Suyash Singh

    Projectile motion and parabola

    Homework Statement A partice is projected at an angle 60 degrees with the speed 10 m/s. Then latus rectum is ? g= 10 m /s^2 Homework Equations i calculated the maximum height.Now what?? The Attempt at a Solution h= u u sin theta sin theta/2g
  7. Y

    Simple Harmonic Motion in x direction

    Homework Statement A simple harmonic oscillator, with oscillations in the x direction, has velocity given by: $$v_{x} = (2.2 \frac {\mathrm{m}} {\mathrm{s}}) \sin [(6.9 \frac {\mathrm{rad}} {\mathrm{s}}) t]$$. Find the values of ##\omega , A, f , T ,## and ##\phi## Homework Equations $$v_{x} =...
  8. L

    Marble rolling on ramp harmonic motion

    Homework Statement A perfectly solid marble of radius R rolls without slipping at the bottom of a spherical bowl of a radius 6R. The marble rolls back and forth in the vertical plane executing simple harmonic motion close to the lowest point. How long does it take the marble to go down one side...
  9. Hiero

    I Center of Mass Motion: Velocity & Momentum

    If we have a system of masses in motion, will the velocity of the center of mass always be given by the net momentum divided by (1/c^2 times) the total energy of the system?
  10. G

    Oscillatory motion equation in sine function

    Homework Statement The equation y = A sin(kx - wt + pi/2) is the same as a. y = -A sin(kx - wt + pi/2) b. y = A cos(kx - wt) c. y = -A cos(kx - wt) d. y = -A sin(kx - wt - pi/2) e. y = A sin(kx - wt + (3pi)/2) Homework Equations y = A sin[(2pi)/lamda * x - (2pi)/period * t + (phase constant)]...
  11. Wrichik Basu

    How to find time period of SHM from equation of motion?

    Homework Statement :[/B] Say for example I've got the equation of a SHM as: $$x = A \cos (\omega t + \phi)$$ where ##A## is the amplitude. How do I find the time period of this motion? Homework Equations :[/B] Stated above. The Attempt at a Solution :[/B] I tried by finding the second...
  12. I

    Need a little help with motion on an inclined plane

    Homework Statement On a plane tilted at the angle of 30 degrees with the horizon lies an object, whose weight is equal to 1.4 kg. The coefficient of friction between the object and the plane is equal to 0.2. Find acceleration. m = 1,4kg; (weight) Angle (A) = 30 degrees. COF µ = 0,2 Ff -...
  13. nagyn

    Spin of a charged sphere in a non-uniform magnetic field

    Homework Statement Consider a solid spinning sphere of negative charge in a non-uniform magnetic field: http://d2vlcm61l7u1fs.cloudfront.net/media%2F2f8%2F2f840122-3d7f-4af3-98a7-efa9b2e7d26a%2FphpBOhfaK.png (the rotation illustrated at the top is supposed to be counter-clockwise). What...
  14. G

    Ways to Spin a Flywheel using linear motion

    I am to try to find simple way to spin a spinning flywheel. What linear motion device acting on the outside edge of a spinning flywheel can be used to increase the speed of the flywheel. Need to use a repeating pattern such as pushing your hand down over and over on the edge of the wheel to...
  15. C

    Uniform circular motion - origin of speed

    I am having trouble understanding tangential speed as it applies to uniform circular motion and I would appreciate any help. Say I have a ball on the end of a string that I hold with my hand and rotate at a constant speed. If the string provides the centripetal force and acceleration, where...
  16. william

    Harmonic motion of loudspeaker

    Homework Statement the cone of a loudspeaker vibrates in SHM at frequecy of 262Hz. the amplitude at the center of the cone is A=1.5X10^-4m and t=0 and x=A (amplitude). 1) what equation describes the motion of the center of the cone ? 2) what are the velocity and acceleration as a function of...
  17. A

    Vertical circular motion in container

    Homework Statement We have an object rotating inside a circular container. The rotation is vertical (see picture below). The radius r of the container is given. Find the frequency (which then ties back to finding the centripetal acceleration) necessary, so that the objects rotating inside the...
  18. Specter

    Circular motion grade 12 physics

    Homework Statement Keys with a combined mass of 0.100 kg are attached to a 0.25 m long string and swung in a circle in the verical plane. a) What is the slowest speed that the keys can swing and still maintain a circular path? b) What is the tension in the string at the bottom of the circle...
  19. W

    Motion of a particle from its momentum distribution

    Hi all, I recently learned the concept of Maxwell's speed distribution and became interested in how to use similar momentum distributions to study the probabilistic motion of a classical free particle. I have done some of my own reading on probabilities and distributions (no formal lessons yet)...
  20. Jay123

    Working on a simple(ish) projectile motion problem for a gaming program

    Hello ladies and gentlemen I am working on a Unity 3d game project and I am in need of some physics guidance. You probably know Unity3d has a built in physics engine, and if you don't you do now. :) I am determined to figure this out more or less on my own but I need some assistance with the...
  21. Spinnor

    I Open string end points, their motion in spacetime

    I have some questions and refer you to the image below the caption of which states, "D-branes may be of exceptional importance in the explanation of elementary particles of the Standard Model. However, it still remains to find a solid connection between the M-theory and the Standard Model."...
  22. F

    Energy conservation in circular motion

    Homework Statement An object of mass m = 1 kg moves along a circular frictionless path of radius R = 0.5 m from point A to point B at which it makes an angle θ with the vertical direction as shown in the figure. If the object is release from rest (VA = 0) and θ = 30° , what is the normal force...
  23. Richie Smash

    Motion of a Door as I Walk by it Quickly (no contact)

    Hey this is just a random question, but recently I've started studying physics, only last year. Before this I never used to question really a lot of things i took for granted, but now I see the world with a different light although I'm still quite the novice. Something that used to make me...
  24. thebosonbreaker

    Why were Newton's laws of motion discovered so late?

    Hi, I had a thought recently which gave rise to a rather interesting query. A helicopter works and is able to fly due to Newton's third law of motion. The propellers rotate at a high speed and exert a force on the air beneath them. By N3L, the air therefore exerts an upwards force on the...
  25. K

    Motion involving speed cameras

    Homework Statement Homework Equations [/B] Equations of motion: v = u + at s = 1/2 (u + v) t s = ut + 1/2at^2 v^2 = u^2 + 2as 3. The Attempt at a Solution Hello, on a i used the 2nd equation: 30m = 1/2 (3*10^8m/s+3*10^8m/s) t so -> t = 1*10^-7s but to get the correct solution i...
  26. V

    Classical mechanics: motion and acceleration

    Homework Statement Referring to the attached diagram, the object ABCD is kept in an isolated system where it is under no external influence of any kind. A· An instantaneous force F acts along the edge BC of the block ABCD, where M is its mass, with its center of mass located at O...
  27. R

    Equation of motion of a Lagrangian density

    Homework Statement from the lagrangian density of the form : $$L= -\frac{1}{2} (\partial_m b^m)^2 - \frac{M^2}{2}b^m b_m$$ derive the equation of motion. Then show that the field $$F=\partial_m b^m $$ justify the Klein_Gordon eq.of motion. Homework Equations bm is real. The Attempt at a...
  28. J

    Relative motion of converging objects

    If two objects are traveling on paths at 90 deg to each other such that they will converge at a point how do we describe that motion. For example 2 cars are approaching a 4 way intersection and will collide. They see each other as moving diagonally yet when they collide one will t-bone the...
  29. T

    Understanding Random Particle Motion in a Monoatomic Gas

    We consider a monoatomic gas in a closed box. A textbook says : Since the assumption is that the particles move in random directions, the average value of velocity squared along each direction must be same. Why the assumption is that the particles move in random directions implies that the...
  30. M

    Solving Linear Motion Problems: Initial Speed, Time, and Height

    Homework Statement "A ball thrown straight up with an initial speed of 30/m/s. (a) Show the time it takes to reach its trajectory will be 3m/s (b) Show that it will reach a height of 45m" Homework Equations h=ut+1/2g^2 1/2gt^2 The Attempt at a Solution Part a of the question I am fine with...
  31. J

    Simple harmonic motion springs

    I have a spring with mass M attached, and leave it at equilibrium. Then I displace it some more by stretching it down a bit more. Displacement due to the mass= X, displacement due to stretching it even more=Y. Why isn't the amplitude of oscillation= X+Y, but is only actually only Y? This is...
  32. R

    Derivation of the Eqation of Motion from Fermi Lagrangian density

    Homework Statement Hello, I am trying to find the equations of motion that come from the fermi lagrangian density of the covariant formalism of Electeomagnetism.Homework Equations The form of the L. density is: $$L=-\frac{1}{2} (\partial_n A_m)(\partial^n A^m) - \frac{1}{c} J_m A^m$$ where J...
  33. F

    Newtonian physics and motion of a wiggling rope

    What types of objects does Newtonian mechanics deal with? Is it just rigid bodies? I’m not sure how Newton’s laws could explain something like the motion of a wiggling rope.
  34. E

    Circular motion and Kinematics

    Homework Statement l=2m b=1.5m The mass of the chair is 5kg. A boy with a mass of 50kg sits on the chair. The distance of the chair from the pole is 3m, and it spins around it horizontally with a radial velocity of 1.95 rad/s. The boy drops a ball at some moment, what would be its distance...
  35. F

    Cirular Motion - car on a circular ramp

    Homework Statement A 1200 kg car has a speed of 5 m/s at the top of a circular ramp of 10 m in radius. The normal force exerted by the seat of the ramp on the car is : A) 9000N B) 9600 N C)11250 N D)13650 N E)14150 N Homework Equations ∑F=ma ac = m v^2 /r The Attempt at a Solution...
  36. K

    Centripetal motion, the tension at the bottom of a circle

    Homework Statement A mass m, at one end of a string of length L, rotates in a vertical circle just fast enough to prevent the string from going slack at the top of the circle. Assuming mechanical energy is conserved, the tension in the string at the bottom of the circle is: a) 6 mg b) mg +...
  37. R

    Projectile motion above ground given only angle and height

    Homework Statement I'm having trouble with part A of this question 1. A ball is fired out at an angle of 30° from the platform of height h = 0.5 m as shown in Figure 1. It is subjected to the gravitational force only thus follows a projectile motion. It falls onto the ground after 0.6...
  38. L

    Exploring Projectile Motion in Reduced Gravity: Calculating Football Distance

    Homework Statement A student can throw a football a max range of 60 meters. How far could he throw it if the Earth's gravity were reducted to 1/6 of its normal value , similar to the moon's gravity? Homework Equations v = .5at^2 The Attempt at a Solution I feel like i did this wrong but x =...
  39. M

    A Lorentz-Einstein law of motion for a point particle

    I shall try to expose my question as briefly and clearly as possible. Within a very old and classical approach (Newton), discussions take place in a three-dimensional Euclidean space and the concept of force is represented by a vector which is proportional to the mass of the object at hand (m...
  40. K

    Circular motion, string and ball in a horizontal circle

    A mass m = 0.15 kg is attached to a massless string and rotates at constant speed v = 4 m/s in a horizontal circle of radius 2 m. The tension T (in N) in the string is: (a) 1.1 (b) 1.9 (c) 2.4 (d) 3.3 (e) 4.9 I would assume that first I calculate the centripetal acceleration by using v^2/r =...
  41. A

    Circular Motion - Hanging object swinging around

    Homework Statement An object of mass m is rotating, hanging from a string of known length l. The string is attached to a pole, which rotates with a known angular velocity ω and forms a to-be-determined angle α with the string. Find α. I think I have solved it (the numbers match the results of...
  42. K

    (Rotational Motion) Calculating maximum velocity.

    Homework Statement If I have an object with mass M. Place it on a spinning disk at radius R and the coefficient of friction is μ what is the maximum velocity I can spin the disk without the object slipping? I have the actual values for the problem, but I'm much more interested in how to get...
  43. N

    B What is the physics of motion through space?

    The metric expansion of the Universe does not seem to cause some of the mechanical effects typically associated with motion (commute) of massive objects through space. For example, distant galaxies can be "flying away" from each other at speeds exceeding the speed of light. It seems that space...
  44. ferrariistheking

    Centripetal Force and circular motion

    Homework Statement Gravity causes a centripetal force that allows satellites to travel around planets. How fast must a 102-kg satellite travel to maintain a circular orbit 352 km above Earth's surface? Homework Equations F=m(v^2/r) -----> (F/m) x r= v^2, then square root F= force m=mass...
  45. F

    Motion predicted by Newton's laws

    Hello The following thought is confusing me a little. Let say we have sphererical planet with a certain mass and radius fixed in space. Now we have a point particle that at time t0 has a velocity vo that is perpendicular to the vector from the center of the plant to the particle and has a...
  46. parshyaa

    Question about circular motion and acceleration

    In circular motion 1) V = rw and ##\vec V## = r ω##\vec e_{tan}## 2) a = rα and ##\vec a## = -##\frac{v^2}{r}####\vec e_{rad}## + rα##\vec e_{tan}## Where ##\vec e_{tan}## is the unit vector along the tangent in increasing direction of θ And ##\vec e_{rad}## is the unit vector along the radial...
  47. J

    Vibration Energy Harvester from Brownian motion

    Hi all, been a while since I studied physics but I saw something that I found strange, This device: https://researchfrontiers.uark.edu/good-vibrations/ from University of Arkansas A free floating graphene sheet extracting energy from brownian motion and converting that to electric current...
  48. A

    Circular Motion — Object on a rotating conic surface....

    I need help understanding what kind of problem this is at all, since I'm really lost. I'm missing the specific topic name (I called the topic "circular motion" because it's got something to do with it, but maybe it has a more specific sub-topic name), probably missing key formulas, and generally...
  49. NoahCygnus

    A question about rolling motion of a wheel on a frictionless surface

    Let's imagine a situation where we have a wheel of mass ##M## and radius ##R## on a frictionless surface, and we apply a force ##\vec{F}## as shown in the diagram. The force will produce both linear acceleration of centre of mass ##a## and angular acceleration ##\alpha##. The wheel starts to...
  50. R

    Particle motion + electric field when voltage varies

    Homework Statement Two parallel plates located at a distance "L" from each other they maintain a potential difference "V" because of a battery (as shown in the picture). Through a small hole, made in bottom plate, electrons get into system (with mass "m" and charge "-e"), with velocity "v" and...
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