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. Ranku

    Escape velocity and gravitational freefall

    Is an object with escape velocity in gravitational freefall?
  2. G

    Find the velocity of the wind relative to the boat

    Could someone please help me see where I am going wrong here? During a race between two boats A and B there is a wind of 18 km/h blowing from due north. The resultant velocity if A is 12 km/h on a bearing of 060. Find the direction of the wind relative to A. My reasoning: (Relative to the...
  3. Amik

    Velocity of the center of mass of the system

    I believe they are the same?I think i am wrong.
  4. Frigus

    Why a force perpendicular to the velocity doesn't change the magnitude?

    As I have shown in the picture even if their is minimal change but shouldn't it increase after a long time as minimal changes will keep accumulating.
  5. wicker558

    Object thrown at an angle: Initial velocity has to equal speed at t

    My solution is very sketchy, but we want the math right. However, I've came to 2 thoughts that helped me get to the solution, and those are: The only way that you can launch a ball at a velocity and have it be the same velocity two seconds later, is if it's already reached its maximum height...
  6. Bob3141592

    I Velocity of Bosons: Massless Particles & Electromagnetic Force

    I get it that nothing can travel faster than the speed of light in a vacuum, and that only massless particles can move that fast. Must move that fast. A photon, the massless boson that carries the electromagnetic force, moves as c, which is given by the inverse root of the electric permability...
  7. Saptarshi Sarkar

    Velocity of a Maxwellian gas

    I expanded it as shown above and got ##<v²> + <\bar v²> - 2<v><\bar v>## = ##v_{rms}^2 + \bar v^2 = \frac {3kT} m+\frac {8kT} {πm}## I used ##<v> = 0## as the velocity is equally likely to be positive as it's likely to be negetive. From the above I get the answer ##\frac {kT} m(3+\frac 8...
  8. Saptarshi Sarkar

    RMS velocity of molecules in a mixture

    I know that for a single monoatomic gas with RMS velocity ##v_{rms}## , $$\frac 1 2mv_{rms}^2 = \frac 3 2k_bT$$ where ##m## is mass of a single molecule, ##k_b## is Boltzmann constant and ##T## is temperature of the gas. For a mixture of gas, I know that the average kinetic energy after mixing...
  9. E

    B Misunderstanding of "proper velocity"

    I've been looking around and have gotten quite muddled about some concepts in special relativity. In the following I won't use four-vectors since I'd like to clear up the confusion first before adding more complexity! The proper velocity/celerity is said to be ##\frac{dx}{d \tau} =...
  10. computing

    Has this particle exceeded 30 km/h on a velocity vs. time graph?

    hi how can i draw velocity - time graph to determine whetere this particle has ever exceeeded the 30 km/h velocity or not ?
  11. polytheneman

    What is the derivative of velocity with respect to position?

    I'm reading a book on Classical Mechanics (No Nonsense Classical Mechanics) and one particular section has me a bit puzzled. The author is using the Euler-Lagrange equation to calculate the equation of motion for a system which has the Lagrangian shown in figure 1. The process can be seen in...
  12. Saptarshi Sarkar

    Terminal Velocity of a Falling Parachutist

    I tried to calculate it by the way I know, i.e., setting the right hand side of the equation of motion to zero and getting v² = 25g = 2500 (taking g =10) => v = 50m/s But this answer is incorrect. How do I use the information of the initial velocity and why would it effect the terminal...
  13. T

    How to find the velocity needed to melt a snowball

    I attempted a solution, but I was unfortunately confused and did not know how to do the problem. As a result, I did not do any work.
  14. E

    Inclined Planes, finding final velocity

    I determined 42m to be the hypotenuse so I used sine law to find the height of the incline, 10.87m. I used this height in the equation Ei=Ef, since they should be equal. Ei=Ef mgh=1/2mv^2 (at the start there is no kinetic energy, at rest. at the end there is only kinetic, no potential)...
  15. J

    G-force experienced by a jumper, using a DE

    We are given that ##v' = \frac{1}{10}v^2 - g##. I tried using implicit differentiation so that ##v'' = \frac{1}{5}vv' = \frac{1}{5}v(\frac{1}{10}v^2-g)## and set this equal to 0. Hence we have 3 critical points, at ##v= 0##, and ##v = \pm \sqrt{10g}##. Calculating ##v''(0)=-120##, we know the...
  16. H

    Finding the velocity of an emitted particle from a decay

    So I know that the total energy of the system initially is 775.5MeV, because the meson is at rest. Also by conservation of energy I know that the total final energy of the system is the same thing. I also know that the initial momentum of the system is 0 because the particle is at rest. This...
  17. Prabs3257

    Velocity of an object on an inclined plane

    I used work energy theorem between initial top point and point x along the incline(downwards) i got the expression of v then diffrentiated it to get a maxima but it gives me a wrong ans which is 10/6 but the actual ans is 10/3 please tell me what i did wrong
  18. B

    Calculating Escape Velocity for Earth: Where Am I Going Wrong?

    I really cannot understand where this is going wrong... Plugging in the constants, I get vescape=Sqrt(2(6.67x10^-11)(5.976x10^24kg)/6378). (6.67x10^-11)(5.976x10^24kg) gives me 3.99x10^14, and multiplied by 2 gives me 7.97x10^14. 7.97x10^14/6378=1.25x10^11. The square root of 1.25x10^11 would...
  19. nineteen

    What is the minimum velocity needed?

    I tried to solve this problem and this is what I could come through: When the object is moving, the force acting on object is the frictional force, so, it got to be μmg. So, F = ma and as F is μmg μmg = ma μg = a So, to find out the magnitude of the initial velocity v given to the smaller...
  20. Arman777

    I Which redshift value is used in the velocity measurement of distance

    Let us say that we have a stellar object so its total velocity is defined as $$ v_{tot} = v_{pec} + V_{rec}$$ Where $$V_{rec} = H_0r$$ and $$V(z) = \frac{cz}{1+z}[1+\frac{1}{2}(1-q_0)z - \frac{1}{6}(1-q_0-3q_0^2+j_0)z^2]$$ for small z.So my first question is what is the $z$ value here? Is...
  21. G

    I Escape Velocity, Gravitational Velocity & Time Dilation

    The is a question about gravitational time dilation and escape velocity. As others have pointed out, you may use escape velocity to calculate gravitational time dilation in a gravitational field. (Interestingly, you can't use gravity to calculate gravitational time dilation, which makes...
  22. L

    A Solved: Velocity of Isolated System in Different Inertial Sys.

    A problem of an isolated system's velocity in different inertial systems, in special relativity ##\ \ \ \ \ ## In the inertial reference frame ##K##, the velocity of each component of an isolated system in ## x## direction is zero at a certain time. ##\ \ \ \ \ ## The inertial reference frame...
  23. H

    Unit of Velocity from a Random Walk measured by an accelerometer

    Hi, I am working on a kalman filter where my measurement equation involves "-g + v" , where g is in m/s^2 and v is velocity random walk given in m/s/sqrt(hr). Feels like a stupid question, but how can I transform the unit of velocity random walk so I can do the calculation correctly?
  24. S

    Calculating Average Linear Velocity: 1.66m/s to 1.73m/s

    First i need the average linear velocity 100L/min = 0.1m3/min 0.00167m3/sec Cross Sec Area = Pie r2 =pie(0.0175m)2 9.61x10-4 m2 0.0016m3/s / 9.61x10x-4m2 = 1.66m/s But my notes say this should be 1.73 m/s Once i have the average linear velocity i can calculate Re. Help appreciated
  25. anonymous99

    What would be the optimum torque/angular velocity for a waterwheel?

    I am designing a pitchback waterwheel for a head of 1m and flow rate of 20l/min. I've calculated that the theoretical power available to me is 3.27W and I know that the mechanical power I can extract is the product of torque and angular velocity but I'm struggling to find information on optimum...
  26. A

    Kinematics without rolling or sliding

    I initially thought it is v, because the speed shouldn't change when the tape is on top.
  27. jisbon

    Angular velocity of a pendulum

    So this question has something probably due to the conservation of angular momentum. I am able to find the moment of inertia about the pivot, which is : $$\dfrac {1}{3}mL^{2}+\left( \dfrac {1}{12}ML^{2}+mL^{2}\right) =\dfrac {17}{12}ml^{2} $$ Now to find angular velocity when angle =0, how am I...
  28. maistral

    2D advection-dispersion velocity component for fluid flow in a pipe

    Pardon if the answers to my questions are obvious, because as usual I am trying to decipher everything on my own (as the material has not been taught to us quite well; then again it's graduate school). I just need someone to reassure me that I am understanding this correctly. Say for example I...
  29. G

    To find the velocity of a mass attached to the midpoint of a spring

    Could I please ask for help regarding part (a) of this question: If I get part (a) then part (b) will follow. So, here's my answer to part (a): I'll be using the formula Elastic Potential Energy in a spring = (Yx^2)/(2a) Where Y is the modulus of the spring, x the extension and a the natural...
  30. J

    Translational and rotational velocity

    For a cylinder rolling down an inclined plane, does the tangential velocity of a point a distance R from the axis of rotation equal the velocity of the center of mass?
  31. B

    Finding the final velocity of a volleyball

    First I calculated the y component of the initial velocity vector: vy1 = 8.5 m/s * sin32 = 4.7 m/s next the change in distance Δd = d2 - d1 = 3.6m - 1.4m = 2.2m Then I put these numbers into the equation v2y^2 = v1y^2 + 2aydy v2y^2 = (4.7 m/2)^2 + 2(-9.8 m/s^2)(2.2m)...
  32. F

    Measuring the Transverse Velocity of a Galaxy

    See the attached figure. I understand that we look for the apparent transverse velocity v , for example through v = d/t (d - distance, t - time). The distance to the galactic nucleus is known as D. Though I am not sure how to read off the time from this figure.
  33. A

    B How to calculate time with delta-v and velocity?

    Is this correct? Why the time is minutes instead of seconds? Thanks!
  34. R

    Exploring Trigonometric Functions & Physics: Velocity, Distance, & Dimension

    Hello, It has been a long time since I first looked at this, so thought I might ask for some help in clarifying this problem: Is an equation of the form --> Velocity = (Distance) * (Trigonometric function) a valid one in physics? If so, what is the relationship of trigonometric functions...
  35. IgorIGP

    B Special case of relativistic velocity addition law

    Hi gentlemen. My model is simple. Imagine, I watch a body which approaches me with velocity of w which value I can measure . I know that this a body has velocity v in a some reference system which aproaches me with same velocity of v. This velocity needs to be calculated (I can not mesure it)...
  36. A

    Angular acceleration and velocity in a circle

    33.33 RPM (1min/60second)(6.28 radian/1 revolution) = 3.45 rad/s linear velocity=3.45 rad/s * 0.1524m=0.526 m/s linear acceleration= (0.526 m/s)^2 /(0.1524m)=1.814 m/s^2 1.814 m/s^2=(0.1524m)(rotational acceleration) rotational acceleration=11.9 rad/s^2 ω1= (3.45 rad/s)+(11.9rad/s^2)(10s)...
  37. hmorenom111

    Finding the equation for final velocity in a perfectly elastic collision

    So after not being able to solve this problem I did some researching online. I was looking around and came across this video, where they give the following equations for solving for the final velocities of both balls: v1f=((m1-m2)/(m1+m2))*v1i v2f=(2m1/(m1+m2))*v1i I plugged in my numbers and...
  38. spacestrudel

    Using Impulse to Solve For the Final Velocity

    Hi there, Just asking a logistics question since I want to be sure I am approaching this problem correctly. My professor showed me an example of a bullet being fired from a barrel, given its initial velocity was 0. The change in time was 0.1 seconds. The mass of the bullet is 0.02 kg. The...
  39. MikeyDoubleDEE

    Need to find the spring constant to achieve Max Velocity

    Hello All. I am mentoring a high school student in my area with his class project for school. He has chosen he wants to launch an object (in our case, a softball) into a 5' diameter area. The idea is to build basically an oversized slingshot using an extension spring as the source of energy. We...
  40. Adi6677

    Velocity of fluid flowing from a hole at the bottom of a conical shape

    My approach was that I consider the pressure of cross section A first Pa= P + dgh Now by writting Bernoulli's Equation between the cross-section A and the opening : $$ Pa + 2dgh + 2dV^2/2 = Pb + 2dV'^2/2$$ Where Pb is the pressure of the opening which is equal to the atmospheric pressure...
  41. J

    Particle bouncing between walls

    I thought it would be a good idea to pretend that the walls are stationary and that each time the particle hits a wall, it gets a velocity addition of the velocity of the wall it’s hitting. Using this I ended up at the formula V = initial velocity of particle + n(velocity of left wall) +...
  42. N

    Solve velocity addition problems using 4-vector

    I used the two equations above to solve for u_x and u_y and got u = 0.987c, where u_parallel = u_x and u_perpen = u_y. I wonder if I can use velocity four-vectors to solve this problem. Modify η'μ = Λμνην so we can use it for velocity addition?
  43. C

    How to find an average acceleration using an average velocity?

    I calculated the average velocity in a previous problem and got 1.146788991m/s over a time of 8.72s. I know I can’t use a_ave=(Vf-Vi)/(Tf-Ti) because I don’t know the final velocity and have no way to find it. Do I multiply average velocity by time?
  44. A

    Escape velocity of an iron asteroid

    Homework Statement: Jack can jump upwards a distance 1.4 meters when he is on the surface of the Earth. What is his initial velocity when he jumps? Most of the time, however, Jack is in space. He is an asteroid miner: he looks for asteroids made out of useful metals. His job involves landing on...
  45. n3pix

    Converting Velocity Formula: Polar to Cartesian

    I have a little question about converting Velocity formula that is derived as, ##\vec{V}=\frac{d\vec{r}}{dt}=\frac{dx}{dt}\hat{x}+\frac{dy}{dt}\hat{y}+\frac{dz}{dt}\hat{z}## in Cartesian Coordinate Systems ##(x, y, z)##. I want to convert this into Polar Coordinate System ##(r, \theta)##...
  46. Like Tony Stark

    Finding angular velocity for a rope to be cut

    I wrote Newton's equations for each body (I took ##x## as the axis aligned with the tension) ##m_1##: ##x)f*_1 -T_1+T_2=0## Where ##f*_1=\omega ^2 r_1## ##m_2## ##x)f*_2 -T_2=0## ##x)f*_2=T_2## Where ##f*_2=\omega ^2 r_2## I wrote that ##T_2=1100 N## and solved for ##\omega##, and I got...
  47. Like Tony Stark

    Finding the angular velocity of a rotating arm

    A) The slider experiments three forces, all of them are on the ##x## axis (considering ##x## axis as the axis aligned with the arm): Normal force (exerted by the support), elastic force and centrifugal force, which is ##m.(\omega^2 r)## Elastic force is equal to ##Fe=-k \delta =-2 (R-2R)=2R##...
  48. M

    Α baseball player throws the ball....

    Hi all ! I wonder if I'm right. (From : Fundamental University Physics, Volume 1 (Mechanics) - (Marcelo Alonso, Edward J.finn) Addison Wesley 1967) This is my try: * I have the Greek version of the book and there is no answer.Thanks.
  49. K

    Closest approach from initial velocity and impact parameter

    Here were my assumptions: Energy and angular momentum are both conserved because the only force acting here is a central force. The initial angular momentum of this particle is ##L = mv_0b## and we can treat E as a constant in the homework equation given above. I solved for the KE (1/2 mv^2) in...
  50. Alexandra Fabiello

    Finding distance east given west dist., velocities, and average velocity

    6.44 km * 1000 = 6440 m/2.51 m/s = 2565.737052 s = west time av = (6440 m + - east distance)/(2565.737052 s + east time) 2565.737052 s + east time = total time 1.28 m/s * total time = (6440 m) - (0.495 m/s * east time) 1.28 m/s * (2565.737052 s + east time) = (6440 m) - (0.495 m/s * east...
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