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. ZdMh

    About difference in Velocity and motion in Jet engines

    I was watching a video about jet engines, and it was obvious for me and for the instructor that if we compress air at high speed from the gas turbine inlet, then after multiple stages collide with the turbines blades inside, the body will move in the sense of difference in velocity, so forward...
  2. Kairos

    B V=dx/dt (relative velocity between two inertial observers)

    In special relativity, when writing the relative velocity between two inertial observers v=dx/dt, I suppose that "dt" is a coordinate time interval? But as it is not measurable, is the velocity correct and the same for both observers if each one uses his proper time intervals?
  3. Mohammad Sakib

    Why the temperature of a car does not increase with velocity?

    We know temperature is a measure of average kinetic energy of molecules/particles of a system. Now if a car starts to move, its velocity increases so does its kinetic energy. Therefore all the molecules are gaining velocity too. Shouldn't this increase the temperatre as average kinetic energy of...
  4. H

    Engineering Highest velocity of a girl running a 60m dash

    So i know the total time is 8.6 s t1 + t2 = 8.6s And from the (v^2 - v0^2 = 2as) i will get that after 15m the velocity which is also the highest velocity v^2 = 30a And then after that the velocity will be constant (s = v*t) 45/t2 Now i am stuck here because i have 3 equations but 4...
  5. B

    2 Carts on a Track Compressed by a Spring -- What are their Velocities?

    a)What is the total energy in the system? Only energy acting on the system assuming the track is level and there is no potential energy of the carts, is the potential energy of the spring. Comes out to 7.8125 using the potential energy of a spring equation. b) What are their velocities if the...
  6. J

    Lorentz Velocity Addition Problem

    So for the formula, u'=u/(δ(1-(uv)/c^2) u=2.06E8 and v=0. I am only looking at the y components here. Since v=0 it really becomes u'=u/δ or u'= u*sqrt(1-(u^2)/c^2)). Anyways when I plug this in I am getting 1.49E8 when the answer should be 0.951E8. Am I not using the correct formula here?
  7. momoneedsphysicshelp

    Finding Angular Velocity in Rotational Motion Problems

    53 rpm equals 5.55 rad/sec multiply 5.55 by 2pi to get angular velocity of 34.8717 Is the answer 34.8717? What should I have done to more accurately solve the problem with a better understanding? What other steps should I take when solving similar problems? and lastly, Is the mass relevant...
  8. T

    Measuring high velocity airflow

    I have a fan that consumes 60 W and blade diameter is 12 inch. If it's just 60% efficient, then the velocity of air coming out of it is around 9.5 m/s. I also have a nozzle inlet of which fits the fan and the diameter at the throat cum exit is 3.5 inch. I want to know how to measure the velocity...
  9. lahanadar

    Cause-effect relation between pressure & velocity

    For a steady, non-viscous and incompressible flow, one can apply both Bernoulli's principle (no potentials) as $$p+\frac{\rho v^2}{2} = p_t$$ where ##p##, ##\rho,##, ##v##, and ##p_t## are static pressure, density, flow velocity, and total pressure, respectively, and continuitiy principle as...
  10. Pipsqueakalchemist

    Engineering Zero Velocity & Acceleration of Point of Contact: Problem Explanation

    For this question the ball is rolling without slipping so that means the velocity of the point of contact is zero. Does that also apply to the acceleration of the point of contact? Because that’s what I assumed and I applied the relative acceleration formula above and use the starting point to...
  11. V

    Determine time after which 4 persons meet in given scenario

    The point of confusion is deciding the direction each persons sets out in i.e. velocity direction of each person. Knowing this will probably help in getting the solution. At t=0, I can say that velocity of each person is as shown in diagram below.
  12. TheArrow

    Calculating Rate of Climb from T/W, L/D and Velocity

    Hello everyone, I'm trying to solve a problem from a textbook suggested by a fellow member here: To help me visualize the problem, I made the diagram below (not necessarily to scale or accurate, just an organizational aid): The textbook gives a simplified equation of...
  13. flyparnape

    Finding the Velocity of a Projectile knowing only Launch Angle and Flight Time

    I don't know the distance or the horizontal velocity so I can't find any logical solution
  14. Pipsqueakalchemist

    Engineering Solving for Angular Velocity at Point A - Confused!

    So for this question I got the right angular velocity. But I don’t get the same velocity for point A. I don’t understand why it’s cos30, problem asked for V_a when theta = 45 so I used cos45. I have my work below.
  15. akashpandey

    Direction of Angular velocity and Angular momentum?

    I am very confused when textbooks say the direction of Angular velocity is perpendicular ot radius and theta for that matter direction is in perpendicular direction. I know this comes from cross product rule but what is the meaning of Angular velocity and Angular momentum directing in upward...
  16. greg_rack

    Special relativity (length contraction, velocity composition) problem

    First, I calculated the velocity of the object with regards to earth, which is: $$v'=\frac{V-v}{1-\frac{vV}{c^2}}=0.34c$$ Now, the problem is solved if I consider the length ##l=45m##(so by calculating the ##\gamma## factor with ##v'##) to be the proper one... but since it's measured by the...
  17. Krokodrile

    Velocity equation and distance problems

    I try to resolved with my knowlegde of the dynamic class: Acceleration is known to be the derivative of velocity with respect to time. a = dv / dt; so that dv = a dt Replace: dv = (2.4 - 0.6v inch/s^2) dt Then: dt = dv / (2.4 - 0.6v inch/s^2); we integrate t between 0 and 2; v between 0 and v t...
  18. J

    Trying to find HOW to get the velocity.

    This is a practice problem so I know that the answer is 750 m/.s. Not totally sure what to do with the friction or if any of my listed equations are relevant here but here goes what I've tried: .45 kg = v(0.8 sec) + 1/2(-9.8 *0.1435) * (0.8)^2 .45 kg = v(0.8) + 1/2(-1.4063) * 0.64 .45=v(0.8) -...
  19. V

    Does the exhaust of a truck match the velocity of the truck?

    My doubt is whether its correct to assume that the exhaust is having the velocity of truck when it comes out of the exhaust pipe. So, I am not sure if Ve = Vt. Should not the exhaust come out in a south direction from exhaust pipe since truck is moving in north direction? If yes, then it cannot...
  20. Pipsqueakalchemist

    Engineering Dynamics rigid body question -- Velocity of points on a car's wheel

    The solutions used the spend of the wheel and its radius to find the angular velocity. I’m confused because I thought to find angular velocity you use the speed at the points of the radius not the translation speed of the wheel itself. Can someone explain this to me please
  21. G

    Einstein velocity addition solving for v

  22. P

    Velocity addition formula in X and Y axes (Relativity)

    The problem: Visualising the problem (My question is with regards to this): Why is the above set-up correct? In the above diagram, S would be moving at velocity -v relative to S', instead of v. Is this because the question says "speed v", and so we can set the direction as such? Why would the...
  23. binis

    I What is the angular velocity of a satellite?

    Angular velocity ω is by definition the runned angle dθ per time dt elapsed: ω=dθ/dt. If the time elapsed in the center of the Earth is dt, the dilated time elapsed on satellite is dt′. What is the satellite's angular velocity? Is it dθ/dt or dθ/dt′?
  24. H

    What is the final angular velocity of the system after the collision?

    I calculated as attached and got it right. However, I just wonder why we can't use conservation of energy as the question has already specified 'frictionless', meaning no energy loss and energy distributed to the rotation only.
  25. H

    Calculating Velocity in the Millikan Oil Drop Experiment

    Hi, I try to find the velocity for a oil drop. I found the forces. ##F=ma => m\frac{dv}{dt} = \frac{4\pi a^3(\rho - \rho_1)g}{3} - 6\pi n a v## with v on the right side, I don't see how to get the solution. I found the solution on few websites, but without the path to find the solution from...
  26. bob1352

    Solving a Problem with Velocity: Stuck and Need Help

    I sent the work divided by two equal to the velocity part of the problem then got stuck.
  27. greg_rack

    Angular velocity of a weighted rod left free to rotate around a pivot

    Hi guys, I don't really know how to solve this problem. The point is finding ##\omega## when ##m_2## passes from ##m_1##'s original position. Ideally, I'm thinking about some conservation of energy/momentum to apply here, but I'm quite confused. Any hint?
  28. G

    Solving for relativistic velocity using Newtonian physics

    The answer is tD = [D_0 - 3/4ct - 1/2ct] I just have 2 questions. I realize for 2 vectors approaching it is negative for distance and for velocity positive. What be the rule for time? How do I find vector answers for velocity and distance and time? I am confused why I have "td = ..." ? Can...
  29. S

    Group velocity dispersion on two pulses of different lengths

    $$\tau _{01} = 10 \tau _{01}$$ If I calculate ##\frac{\tau_{p1}}{\tau_{p1}}## and set z=d=1cm I do not know how to continue from there as I can't solve the equation without knowledge of τ0 for D. $$\frac{\tau_{p1}}{\tau_{p1}} = \frac{\tau_{02} \cdot 10}{\tau_{02}} \sqrt{\frac{1+\frac{d^2 \cdot 4...
  30. B

    What is the angle between the acceleration and velocity when rotating?

    ##ω = \frac {k} {\sqrt{φ}}## What is the angle between acceleration and velocity after 1spin (2π radians)? First I decided to find out what is the angular acceleration: ##α = \frac {dω} {dt} = \frac {dω} {dt} \frac {dφ} {dφ} = \frac {dω} {dφ} ω \implies ##after integrating ##\implies α = -...
  31. Strand9202

    Velocity of an Object given its position as a function of time

    Attached is the problem and my work through the problem. I got the problem correct, but my teacher said this could be done quicker on a calculator. Any idea how it could be done quicker.
  32. dahoom102

    Getting the angular velocity using the angular acceleration graph

    The answer here is A What i did is getting the area as follows, 2×4×1/2 +3×-6×1/2 +4×-6 = -29 and then use this Δω=ωf-ωi -29=ωf-5 ωf=24 but there is no such choice.
  33. J

    B Velocity Addn Paradox: SR Postulate Explained

    Velocity addition paradox: In observer A's frame, observers B and C move away from him at the speed of light c, B to the left and C to the right. In B's, frame A and C are both moving away from him at c, i.e. at the same speed. In both A's and C's frames they are moving at different speeds...
  34. ilper

    Constant velocity in a central force field

    A body on a circular orbit in the field of a central force (satellites in gravity field of Earth; a charge in a magnetic field) is subjected to a force which is always perpendicular to its initial velocity v, hence in a time period dt it acquires an additional velocity dv, which is also...
  35. duchuy

    Determine initial velocity of a vertical throw

    Hi, I was given this problem saying that a ball is thrown vertically up in the air and returns to its initial position after 4 seconds. The acceleration due to gravity is given to be equal to 10m/s^2. I tried to attempt this problem by using the equation : v^2 - v0^2 = 2ah by considering...
  36. S

    Understanding Griffith's Velocity Argument for Charge Integration

    In Griffith’s section 10.3.1, when proving why there is an extra factor in integrating over the charge density when it depends on the retarded time, he makes the argument that there can only ever be one point along the trajectory of the particle that “communicates” with the field point. Because...
  37. J

    Finding the maximum velocity and PE of the block between 2 springs

  38. J

    Expressing horizontal velocity as a function of time for a wave

    This is more of a conceptual question. To find the horizontal velocity as a function of time for the above wave function, you take its partial t derivative and insert x=4. In other words the function would be -2.4sin(1-12t). Im wondering why you take the partial t derivative and not to partial...
  39. momoneedsphysicshelp

    Solving for the velocity of a Pendulum

    I think the answer is 6.2 but I also got 40m/s. Which one is right?
  40. Leo Liu

    Conservation of energy in a CM system moving at constant velocity

    My book uses ##1/2m_1v_{1c}^2+1/2m_2v_{2c}^2=1/2m_1v_{1c}'^2+1/2m_2v_{2c}'^2## to show that the angles of deflection of the collision between two particles are the same in the centre of mass frame. However, I am doubtful that one can apply the conservation of energy to a "moving" system because...
  41. winnie_d_poop

    Prove that the derivative of the position vector equals the velocity vector

    1.)##\dot{\vec{r}}=\dot{x}\hat{i}+\dot{y}\hat{j}+\dot{z}\hat{k}=\dot{r}\hat{r}## since the unit vector is constant 2.) ##\dot{r}\hat{r}=\frac{x\hat{i}+y\hat{j}+z\hat{k}}{\sqrt{x^2+y^2+z^2}}\frac{\dot{x}x+\dot{y}y+\dot{z}z}{\sqrt{x^2+y^2+z^2}}##...
  42. SebastianRM

    Slip Conditions for flow between Parallel Plates

    The problem states: Two parallel plates separated by distance h, the plate at the top moves with velocity V, while the one at the bottom remains stationary. My initial approach was: I considered, ##du/dy = V/h## and for the shear stress ##\tau = \mu \frac{\partial u}{\partial y}## For...
  43. R

    Relativistic Relative Velocity Problem

    Heres how I tried to set up the problem. I took the laboratory to be S and the frame of the particle whose speed we know to be S', so that the speed of S' relative to S is u = 0.65c. Also, by convention, S' moves to the right of S, so that S moves to the left of S'. Next, we know that the...
  44. F

    I Does mean velocity equal group velocity of wave packets in QM?

    Does mean velocity of particle equal group velocity of wave packet in QM?If they do not equal which of them is classical velocity?
  45. A

    Engineering How to find the angular velocity of a rotating drum?

    Good day here is the exerciceThe only velocity I do have is the velocity v os the center of pulley 5, I tried to find the center of instantaneous velocity to find the angular velocity of pulley 5 but I couldn't, any hint would be highly appreciated! Best regards!
  46. J

    Can the velocity in a funnel be higher than in freestream?

    If I put funnel out of car when driving 100km/h, can speed in narrow section in funnel be higher than 100km/h(freestream) and does bernuli equation works for this case?
  47. mattlfang

    Find the velocity and acceleration of a pulley in a mass-spring system

    This looks like a classical setup but I can't find a solution. We can calculate the energy of the system by looking at the work done by the gravity and the spring. But how do we divide the energy between the kinetic energy of the pulley and the rotation of the pulley?
  48. E

    I Relativistic Velocity, Perp. Accel., Momentum: Explained

    A stationary observer sees a particle moving north at velocity v very close to the speed of light. Then the observer accelerates eastward to velocity v. What is its new total velocity of the particle toward the north-west relative to the observer? I ask because while the particles total...
  49. Leo Liu

    Sum of oscillating frequency and angular velocity

    The "egg" initially spun around axis 1 with at ##\omega_s##. After being disturbed, it has started to possesses angular velocities along 2 and 3. The question is to find the rotational speed of ##\vec \omega=\vec\omega_1+\vec\omega_2+\vec\omega_3## to a fixed observer. It is calculated that...
  50. PhysicsTest

    To find the parameters of velocity in an electric field

    i have drawn the E field as below, hence the F will be in the upward direction for electron a. Using energy is constant, the velocity ##v_x## as it crosses A is ##0.5mv_x^2 = q*V_a## ##v_x = \sqrt{(\frac{2qV_a} m)} m/s## one doubt i have here is, the question mentions electrons, but i have...
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