What is Velocity: Definition and 1000 Discussions

The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object's speed and direction of motion (e.g. 60 km/h to the north). Velocity is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of bodies.
Velocity is a physical vector quantity; both magnitude and direction are needed to define it. The scalar absolute value (magnitude) of velocity is called speed, being a coherent derived unit whose quantity is measured in the SI (metric system) as metres per second (m/s or m⋅s−1). For example, "5 metres per second" is a scalar, whereas "5 metres per second east" is a vector. If there is a change in speed, direction or both, then the object has a changing velocity and is said to be undergoing an acceleration.

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  1. Lay1

    Finding the acceleration of the ball in contact with the ground during bouncing

    the v before hitting the ground immediately=4.85m/s the v after hitting the ground immediately= 3.96m/s I considered the down positive, then v= u+at 3.96= 4.85+ (a*0.16) so a= -5.56m/s*s The answer is 55m/s*s The parts that I don't get are why it must be -3.96 and why that velocity becomes...
  2. A

    Finding kinetic energy and initial velocity of a cart over time

    Here's my list of variables and things to account for: m=100kg Wnc=5000J Wfriction=-500J -Kinetic energy will be doubled (though I don't know how that plays into it exactly) -I don't think there's any PE because it's on level ground My idea of what the equation might be: Wnc +1/2mv^2initial =...
  3. Stewkatt

    Motion of an Object: Displacement & Average Velocity

    An object starts from rest and accelerates at 3.0 m/s2 for 4.0 s. Its velocity remains constant for 7.0 s, and it finally comes to rest with uniform deceleration after another 5.0 s. Find the following: a. the displacement for each stage of the motion b. the average velocity over the whole time...
  4. B

    The Traditional Bernoulli Eqn Derivation of Rocket Exhaust Velocity

    If you've seen it, they chose one point in the combustion chamber and the other in the exhaust nozzle. I think they're assuming that we have a gas both places. They say that the pressure in the nozzle is atmospheric pressure, or it you're in outer space, zero. That makes perfect sense...
  5. frost_zero

    I Hypothetical Velocity Faster Than C: Exploring Relativity

    I know it isn't possible for any mass/massless body to have velocity more than the speed of light in vacuum but what if it was done hypothetically? As far as I know length and time of an object undergo a transformation so that the laws of physics remain same between observers at rest and...
  6. P

    B What gives satellites their tangential velocity?

    What gives satellite a tangential velocity?
  7. J

    Velocity, traveling distance and friction force on a sliding object

  8. Remixex

    Estimating the velocity of seismic waves through an idealized Earth

    Hello, this is a repost from a much less-clear question I posted before (link to question: https://www.physicsforums.com/threads/triangles-inside-a-circle-to-represent-raypaths-inside-an-ideal-earth.1011998/#post-6596165). It's kind of a loaded question, however it can be expressed as triangles...
  9. J

    What is the relationship between angle and static friction?

  10. Istiak

    Velocity along the cylinder axis

    Since the question says that "velocity along the cylinder axis" and "magnetic field perpendicular to the cylinder axis". So cross product of velocity and magnetic field becomes their magnitude. ##\vec v\times \vec B=||v|| \\ ||B||## So ##\vec F=qvB## ##mg=qv\frac{\mu_0 nI}{4\pi r}## At first...
  11. jellybean-spider

    Fields (Gravitational fields) -- Escape Velocity from the Moon

    It's an MCQ, and I chose 4/81 v(esc). Is this correct? There isn't a marking scheme... :cry:
  12. e2m2a

    How can velocity be plotted in Vpython?

    Can someone tell me how to plot/graph velocity in vpython? All the documentation I see just deals with plotting the position of the object, nothing on plotting the velocity.
  13. Istiak

    Find out velocity of an observer (relativity)

    Initial observer is at rest. So ##x\prime=0##, and according to question they are 10 meter apart. So lorentz transformation becomes ##vt=x## ##v=\frac{x}{t}## ##=\frac{10 \\ \mathrm m}{13\times10^{-9} \mathrm s}## But I don't get the expected answer. I believe if I had took ##\beta c## instead...
  14. Istiak

    Find the equation of this magnetic field

    When I try following numbers from internet then I don't get an expected answer. ## \mu_0 = 1.25663706 × 10-6 m kg s^{-2} A^{-2}## ##q =1.60217662 × 10^{-19} coulombs ## ##r=2.82x10^{-15} m## Velocity of that electron is given in question ##\vec v= 2 \times 10^6 \\ \mathrm{ms^{-1}}##Since...
  15. rudransh verma

    Integration of velocity to get displacement

    Integration of v= integration of##(alpha \sqrt x)dx##. But I am getting wrong answer.
  16. P

    The velocity of a movable block that is penetrated by an arrow

    This problem is in a chapter on momentum in the book basic engineering mechanics explained. Help me Mario
  17. Istiak

    Find second object's velocity in relativity

    > A particle of mass M at rest decays into two particles of masses m1 and m2 traveling in opposite directions at velocity v1 and v2 respectively. Express v2 in terms of v1, m1, m2, and M. Since both objects are from a single object that's why I took relativistic mass of both objects are same. I...
  18. rudransh verma

    B Speed/velocity as a derivative

    [Note: Link to the quote below has been pasted in by the Mentors -- please always provide attribution when quoting another source] https://www.feynmanlectures.caltech.edu/I_08.html Let s=16t^2 and we want to find speed at 5 sec. s = 16(5.001)2 = 16(25.010001) = 400.160016 ft. In the last...
  19. R

    Mass, acceleration and velocity

    Good Evening All, I have an assignment i am struggling with really hope you can help. The question reads Describe how force, momentum, Angular momentum, kinetic and potential energy are linked with respect to mass, acceleration and velocity I know the following Force – the push or pull...
  20. Send-Help

    Find tangential velocity given radius and the coefficient of friction

    I have attempted to solve for the velocity by setting the centripetal force (mv2)/r to the normal force pointed to the center of rotation (mg). This approach seems to give the incorrect solution and I am unsure of my misunderstandings.
  21. R

    SOS -- Questions about mass, acceleration and velocity

    Please some one help! I am about to go stir crazy. I am really struggling to answer a the following question...describe how force, momentum, Angular momentum, kinetic and potential energy are linked with respect to mass, acceleration and velocity. Its probably really easy but science is not my...
  22. e2m2a

    I Angular Velocity: Vector or Not?

    I understand that angular velocity is technically not a vector so does that mean the cross product of the radius vector and the angular velocity vector, the tangential vector, is also not a vector?
  23. M

    B Measuring Light Velocity Correctly: Thought Experiment

    Let there be a track 450,000 km long and a rocket 300,000 km long with a laser attached to the bottom of it's back end with a clock beside it, and a second synchronized clock attached to bottom of its front end. Both clocks were also synchronized with a track clock while the rocket was parked...
  24. S

    Calculating the velocity of a head-on impact between two suns

    Firstly I would like to start with solving the problem with energy conservation principle which most solutions to the question show. -Gmm/r= 1/2 mv^2 +1/2mv^2 -Gmm/2R Where m= mass of planet r= initial seperation v= final velocity. R=...
  25. binis

    A How is phase velocity related to deflection angle?

    Refractive index is a function of velocity in the medium. How is this related to deviation angle inside the medium? I am not asking for the known formula, but for the mechanism behind it.
  26. duchuy

    Determine the velocity of a particle in mass spectrometry

    Hi, I am trying to determine the velocity of the particle with the mass m coming out of the acclerator. I tried writing : Ep(i) + Ec(i) = Ep(f) + Ec(f) Ec(f) = Ec(i) - Ec(f) But at this step, I'm no longer sure how to express Ep with V because : In my textbook, it's written : Ep = 0,5...
  27. F

    I How to change CSpice initial velocity from an Asteroid SPK file?

    Hello, I've made a SPK file for asteroid 7482 (1994 PC1) with Horizon. I wan't to change the initial velocity with cspice, because I want to know where it will be in a future time at the speed changed. (now I'm using Newtons calc but is slow an error increases with time). This is for calculating...
  28. chwala

    Find the velocity of the airplane if there was no wind

    Find the question and its solution below; Ok i realized that we could also use cosine rule here, in my approach i considered the sketch below; ##V_b= 18,125- (2×50×125×cos 135)## ##V_b=164.2## To find direction, i used sine rule; ##\frac {125}{sin α}##=##\frac {164.2}{sin 135}## ##α=32.56##...
  29. AntSC

    Acceleration-Time Graph and Velocity Multiple Choice Question

    The variation with time t of the acceleration a of an object is shown What is the change in velocity of the object from ##t=0## to ##t=6##? A. ##6ms^{-1}## B. ##8ms^{-1}## C. ##10ms^{-1}## D. ##14ms^{-1}## So apparently the answer is B, which I am having trouble reconciling. Using methods...
  30. K

    B Locus if velocity component is zero

    Figure shows a locus of the figure axis of a symmetrical top on a unit sphere such that ##\dot{\theta}=\dot{\psi}=0## at the upper bounding circle. Where ##{\theta}## is the polar angle and ##{\psi}## is the azimuthal angle. Suppose the figure axis is at the upper circle, since...
  31. LCSphysicist

    Wrong sign in my answer, why? SR + Addition of velocity....

    Adopt the speed of light equals one. Calls ##cos = c##, ##sin = s## $$ux' = \frac{v-uc}{1-uvc}$$ $$uy' = \frac{us}{\gamma(1-uvc)}$$ $$tan \theta' = uy' / ux' = \frac{us}{\gamma(v-uc)}$$ So that's basically my solution. The problem is: The answer is ##\frac{us}{\gamma(v+uc)}##. Now, i can't...
  32. T

    Sonic velocity at the throat of a convergent-divergent nozzle

    Sufficiently pressurised (difference between inlet and release pressure is enough to create supersonic flow) gaseous fluid is being released through a convergent-divergent nozzle. And it's a known fact that if pressure difference is sufficient, a convergent-divergent nozzle can release gaseous...
  33. Iwanttolearnphysics

    Help Me Solve This Khan Academy Question: Friction and Initial Velocity

    Here's a picture of the question: This is a Khan Academy question and although I could just click on hint to find out what the answer is, I think it would be helpful to still ask this here before looking at the answer over there, so that I know what I did wrong. Thank you in advance to anyone...
  34. D

    Angular velocity of pinned rod

    My line of thinking is as follows: \omega_{PQ} = \frac{v_{\perp}}{\ell} = \frac v\ell \frac{\sqrt3}{2} Similarly for rod ##QR## \omega_{QR} = \frac{v_{\perp}}{\ell} = \frac v\ell \frac{\sqrt3}{2} Is my reasoning correct?
  35. G

    B What experiments confirmed the constant velocity of light?

    What other experiments, besides the M&M experiments confirmed the constant velocity of light? Thank you in advance for the response.
  36. Iwanttolearnphysics

    About Work done when velocity is constant

    Here's where I got the questions: These are from a worksheet I downloaded online: Answer Key The answer key says that the answer to the first question is 500J and for the next question it's 433J. It says constant speed though, so I don't understand why the answers aren't zero. I get how they...
  37. L

    Calculate the angular velocity for each case

    First case, descends with the wheel: mgh = .5(I)(w^2) ———- GPE converted to wheel energy w = .1095. ———- rotation result is .1095 Second case, allow to free fall and impulse: mgh = .5(m)(v^2). ———- GPE converted to kinetic energy v = 7.746 ———-...
  38. E

    Velocity vector addition problem

    Hello, guys. Interesting riddle here. I have no idea how to solve it. Tried different methods, but point is answer is always wrong, exact answer Downriver, at an angle of 53.13(degree) to the bank. That exercise is from "Pohl’s Introduction to Physics"
  39. P

    Angular velocity of rod and bug

    I(i)w(i)= I(f)w(f) I(i)= 1.08 x 10-3 kg·m2 w(i)= 0.221 rad/s I(f)= mr^2 + I(i) = (5 x 10^-3)(.138)^2 + (1.08 x 10^-3) (1.08 x 10-3)(.221) = ((1.08 x 10^-3)+9.22 x 10^-5))w(f) w(f) = (2.3868 x 10^-4)/(0.00117522) w(f)= 0.203094 rad/s This is my attempt; however, I cannot seem to get it...
  40. J

    Solving for Distance, Velocity and Acceleration

    Distance: substitute t=5 into x=3e^(0.4t) 22.17m Velocity: v=dx/dt =1.2e^0.4t____(1) Sub t=5 back into (1) v= 8.867m/s Acceleration: a=dV/dt =0.48e^0.4t____(2) sub t=5 back into (2) a= 3.547 m2/s I am not sure if i am doing this right on dx/dt and dv/dt
  41. brochesspro

    Relative Velocity of a Passenger Hitting the Dashboard in a Car Crash

    Where exactly have I gone wrong? I think it is the part where I assume that the person gains the deceleration of the car, but I have no other way to proceed in this case. Also please only use the equations that I have posted below, and it would help if you would not use the equation for...
  42. Andrew1235

    Mass conservation in a sphere to find radial velocity of a flame

    I am not sure what form of mass conservation to use to solve the above problem from An Introduction to Combustion by Stephen Turns. Can anyone explain what form of mass conservation applies to a sphere in this context?
  43. J

    I Does Escape Velocity depend on a rocket's direction away from Earth?

    He explain escape velocity in example where rocket goes straight up,isnt escacpe velocity ,velocity where centrifugal forces and gravity are equal,so refers only when rocket going in circle/orbit? Can rocket really leave Earth in straight line like he show in video once reach this velocity and...
  44. kara123

    Solving for Time Given Acceleration & Initial Velocity

    assuming initial velocity is 0 and we have the value for acceleration I'm unsure how to still use any of those equations because you must have a time value at least or a final velocity
  45. A

    Trouble with Part B of Physics Problem: Velocity

    I am having trouble with part b). I found the answer to part a) is -0.4 and for part b) the mark scheme says that the velocity of the 2nd bag is 1.6m/s but how do I find that out? If someone could perhaps show step-by-step of part b)? Thank you!
  46. J

    Working out steam velocity with only pressure difference

    I am currently doing an assignment on nuclear power and in the turbine, the steam is moving from pressure of 6Mpa to 0.008 Mpa. is there any way to work out the velocity of the steam when moving between these pressure differences?
  47. P

    How does a mass moving up a ramp change its velocity?

    A point mass is moving at speed v, on a horizontal plane, until it reaches an incline. Immediately after just climbing up the incline, its speed remains at v, but its direction changes. How does this happen? Q2: Now, I drop a point mass such that it falls vertically downward onto a fixed ramp...
  48. P

    Bragg curve -> observing dependence on velocity

    We can read: "The velocity dependence of the stopping power, increasing with decreasing velocity, is obvious from Fig.4". I know why the stopping power depends on velocity as Bethe equation states, but I do not know how I can observe that dependence on a Bragg curve.
  49. rudransh verma

    What kind of motion is this? (bicycle velocity vectors)

    How the heck the bicycle reach from point A to point B with that velocity vector directions?
  50. Physil

    An expression for the vertical velocity as a function of time

    A rocket of initial mass m0 is launched vertically upwards from the rest. The rocket burns fuel at the constant rate m', in such a way, that, after t seconds, the mass of the rocket is m0-m't. With a constant buoyancy T, the acceleration becomes equal to a=T/(m0-m't) -g. The atmospheric...
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