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. V

    Find the point when velocity is momentarily zero

    Homework Statement [/B] A block travels in the positive x-direction with some velocity ##v_0##. It is subject to a drag force $$F(v)=-F_0e^{Kv},$$ where ##F_0,\,K## are positive constants. Find the point in time when the velocity of the block momentarily goes to zero. Find how far the block has...
  2. B

    Calculate final velocity of electric particle

    Homework Statement A particle of mass 7.3 × 10−5 g and charge 24 mC moves in a region of space where the electric field is uniform and is 6.3 N/C in the x direction and zero in the y and z direction. If the initial velocity of the particle is given by vy = 4.1 × 105 m/s, vx = vz = 0, what is...
  3. S

    Velocity Vectors of a Boat Relative to the Shore and River

    Homework Statement The water in the river moves southwest (45 degrees south of west) at 4 mi/h. If a motorboat is traveling due east at 15 mi/h relative to the shore, determine the speed of the boat and its heading relative to the moving water. Homework Equations Vector summation The Attempt...
  4. E

    Calculating Surface Shear Stress in a Boundary Layer with Given Velocity Profile

    Homework Statement If the velocity v of the air in a boundary layer having a dynamic viscosity of 18x10-6 kg/ms is given in terms of the distance y from the surface by v = ay + by2 where a and b are constants, calculate the surface shear stress if at 1.5 mm from the surface the velocity is 75...
  5. M

    I Understanding Time Dilation and Velocity: Debunking Common Misconceptions

    Hello. I have a question. If I am moving with velocity v for an observer O. If I experience and kind if time dilation and my time slows down with respect to observer O's time. But if my time slows down. For O I will be moving slowly in time. If time dilation is large enough. I will almost freeze...
  6. D

    Velocity Potential of a Moving Cylinder

    Hi, i need help in deriving the velocity potential of a moving 2D cylinder (circle) in potential fluid. The cylinder is moving in negative x direction U(t). I can derive the velocity potential of fluid past a cylinder (cylinder is stationary, in which it is the scalar summation of uniform...
  7. Rainie Metis

    Comparing Crushing Forces: Human vs. Fly

    Homework Statement Hello All, I might be at best HS level physics understanding but I’m quick study and need guidance. I am in a debate with someone who thinks a body can be crushed to the point of dust. I’d like to know if a comparison can be made, basic ratio: Human crushed by a building at...
  8. K

    Is the Velocity of the Grapple Accurate Using Jacobian's Transformation?

    Hello! I have some problems with geometry/kinematics, therefore i require in your help. :nb) I need to estimate the velocity of manipulator's grapple. I have found one solution (with the use of Jacobian's transformation), but i don't know, right it or wrong. Let's check together :wink: Maybe...
  9. jonnybmac

    Linking gravity, angular velocity and radius

    Homework Statement I am having trouble linking gravity to the radius of the Earth and angular velocity. I was using this as a solid method to confirm the equation for values of a different sort based on centripetal acceleration. When inputting the values though it does not add up and I cannot...
  10. C

    Velocity of a cylinder on a horizontal plane

    Hi, I appreciate any help. Thanks in advance! Homework Statement The image shows the top view of the set-up. Basically, it is a cylinder (resting on a horizontal plane) with two rods on either side attached in line with the centre of mass of the cylinder. Two pieces of string are then taped...
  11. B

    Initial velocity of ball B hit a free falling ball A

    Homework Statement A boy release ball A from height 5m from ground at the same time other boy throw ball B vertically upward to exactly strike ball A. When ball B released it was 1m from ground find minimum initial velocity of ball b. Given g=10m/s^2 a) 2m/s b) 3m/s c) 4m/s d) 5m/s Homework...
  12. S

    Finding the velocity of flow described by a vector field

    Homework Statement Consider the surface, S, in the xyz-space with the parametric representation: S: (, ) = [cos() , sin() , ] −1/2 ≤ ≤ 1/2 0 ≤ ≤ os(). The surface is placed in a fluid with the...
  13. F

    What is the Velocity of Thermal Neutrons at 25 Degrees Celcius?

    Homework Statement Estimate the velocity of thermal neutrons at 25 degrees celcius Homework EquationsThe Attempt at a Solution I attempted to use KE=0.5mv^2 but I realized that I didn't know the Kinetic energy
  14. Abhimessi10

    Difference between relative velocity and effective velocity

    Can anyone tell me the difference between concept of relative velocity and effective velocity and when to use the concept of relative velocity? For example, if a guy throws a ball from a moving object at an angle theta it undergoes projectile motion we write horizontal velocity as...
  15. K

    Finding the units in an algebraic equation for velocity

    Homework Statement During a short interval of time the speed v in m/s of an automobile is given by v = at^3 + bt^4 , where the time t is in seconds. The units of a and b are respectively: (a) m⋅s^2 ; m⋅s^4 (b) s^3/m; s^4/m (c) m/s^2 ; m/s^3 (d) m/s^3 ; m/s^4 (e) m/s^4 ; m/s^5 Homework...
  16. X

    Velocity of the center of mass for MD simulations

    When calculating the center of mass for an MD simulation, I've seen a few codes that subtract the average velocity from each atoms velocity. I think the reasoning behind this is that you want the velocity of center of mass for the simulation to be zero, which I understand, but I don't understand...
  17. M

    Air flow velocity - big to small and vice versa

    Hi there, prob a simple question for you physics gurus, but this application is for a race car, and question relates to air flow velocity through a pipe, in particular exhaust and intake. Now, my thinking for the exhaust (push) is that by going from a small diameter to a large diameter will...
  18. karush

    MHB Eb3 Velocity and Time: Calculate $V_{av}, v_{av}$, and Time to Fly $3.5 \ km$

    1 What must your car’s $V_{av}$ be in order to travel $\textbf{235 km}$ in $\textbf{2.75 h}$ \begin{align*}\displaystyle V_{av}&=235km/2.75h \, km/h \\ &=\color{red}{85.45 \, km/h} \end{align*} 2 A particle at $t_1 =–2.0 s$ is at $x_1 = 4.8 cm$ and at $t_2 = 4.5 s$ is at...
  19. Pushoam

    Calculating angle between velocity and position vector

    Homework Statement Homework EquationsThe Attempt at a Solution I took ## \frac { d\vec r}{dt} = 0 ## . This gives ##t_m = \frac { 1} {\sqrt{ 2}} ## ...(1) To calculate ## \alpha ## , ## \cos{ \alpha } = \frac { \vec v \cdot \vec r}{|\vec v||\vec r|} ## ...(2) Then, magnitude of...
  20. scott ketter

    What is the final velocity of a ball rolling through a tube?

    I am making a physics simulator and this problem is tricky. You have two freely moving objects with known masses and velocities in a frictionless environment. The first object is a ball and the second is a pipe. They are moving toward each other. I need to know what formulas are used to simulate...
  21. Dank matter

    Velocity persistence in Chapman-Enskog theory

    Hi guys! My question is about the diffusion coefficient of the mixture of gases. Consider two gases in thermal equilibrium (Maxwell velocity distribution) having different densities n1 and n2. Let's suppose that the molecules are rigid spheres with diameters d1 and d2 and masses M and m...
  22. W

    Change in Momentum of a Hockey Puck

    Homework Statement A hockey player hits a slap shot, exerting a constant force on a 3.06 kg puck for 0.06 seconds. What is the change in momentum of the puck? Homework Equations Impulse = Mass x (Change in velocity) = Force x time (I think that’s all needed? Most likely missing one.) The...
  23. PhysicallyAmazing

    I Velocity Relativity: Solving a Complex Problem

    A problem I struggle to conceptualise as I have began leanring about relativity and seek your guidance and knowledge on: Consider a stationary observer at point A. Relative to the observer there is a train traveling at -0.6c. A passenger on board the train has a particle gun, and fires it in...
  24. Pranav

    B F=ma -- True or an Illusion....

    Imagine, There's a ball in deep space traveling with a constant velocity of 25m/s and is having mass 25kg. Now as I said, ball is traveling with a constant velocity that simply means acceleration=0 and now if we calculate the force with F=ma we will end up with 0. But if that ball collide with a...
  25. T

    Is the velocity of this object increasing or decreasing?

    Homework Statement Hi everyone, 8th grade physics teacher here. We are doing a handout where we have to identify time-velocity graphs with descriptions. Can you help me with this one? https://imgur.com/a/vEIkg A) The velocity is increasing at a uniform rate. B) The velocity is decreasing at...
  26. Alexanddros81

    A block is released from rest, determine its velocity

    Homework Statement 14.10 Solve Prob. 12.47 by the work-energy method 12.47 When the 1.8-kg block is in the position shown, the attached spring is undeformed. If the block is released from rest in this position, determine its velocity when it hits the floor Homework EquationsThe Attempt...
  27. E

    Velocity and Distance involving springs

    Homework Statement A spring with an elastic constant of 120 N/m is compressed 0.2 m, then launches a block of mass 0.5 kg on a table with friction 0.49, and it travels 0.9 m before stopping. If the block is then released at the edge of a table top 1.2 m above the ground, how far will the block...
  28. I

    A weird velocity/acceleration question

    Homework Statement This problem showed up in my final review packet, and I /think/ it should be basic kinematics, but I don't even know how to approach it with the second half of it. An object moves according to the equation x = vt + ke^(bt), where k, v, and b are constants, x represents...
  29. R

    Gravity, friction and tangential velocity

    Hi everyone, Me and a friend discussed a problem relating to a rotating reference frame, and somehow got to this question which we can't fully figure out, or maybe we are missing something. so, here goes: On Earth's equator, our tangential velocity is ~1700 km/hr. A satellite orbiting right...
  30. L

    Help with Final Velocity Collision Problem

    Homework Statement Homework Equations change in momentum = m1v1 = m1v1+m2v2 center of mass = m1x + m2x / (total mass) The Attempt at a Solution m1v1= m2v2 + m3v3 m1 = 2 v1 = 4 m2 = m1 divided by 2 m3 = m3 divided by 2[/B] 2*4 = 1*12 + 1v3 v3 = -4 v3= -4? in the x directioncenter of mass...
  31. L

    Finding a bullet's velocity over time

    Hi, I engage in physics as a hobby, and I'm not extremely familiar with things reaching into calculus levels of math. That said, how would I find the velocity of a bullet at a given time or distance, taking wind/humidity/etc. out of the equation? I know the muzzle velocity only applies to the...
  32. karush

    MHB UP 2.1 Rocket Average Velocity

    $\tiny{UP 2.1}$ $\textsf{A rocket carrying a satellite is accelerating straight up from the Earth's surface}$ $\textsf{At 1.15 after liftoff, the rocket clears the top of its launch platform, 63m above the ground.}$ $\textsf{After an additional 4.75s it is 1.00km above the ground.}$...
  33. K

    Solve Physics Q: Acceleration & Velocity of Object

    An object, moving in a straight line, has a velocity of 5.0 m/s at time t = 0. From t = 0 to t = 5 s its acceleration is 2.5 m/s2 , while from t = 5 to t = 11 s its acceleration is - 0.1 m/s2 . Over the time interval t = 5 s to t = 11 s its average velocity is: (a) 15.0 m/s (b) 12.5 m/s (c) 17.2...
  34. L

    Finding the angular velocity of a rotating rod

    Hi everyone, sorry for bothering y'all again but here is another problem that I'm struggling with! This is the question and the professor's solution guide: When I solve the problem, I always end up getting 7.67 rad/s instead of 3.83 rad/s. My understanding of the solution is this: This is...
  35. 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...
  36. I

    Is Velocity Conserved in an Elastic Collision Between Two Cars?

    My question is, in an explosion, where 2 cars at rest are pushed apart by a spring between them, is velocity conserved? Does the total velocity for both cars before spring release equal the total velocity after release? Why or why not?
  37. S

    Velocity to land 1/4, 1/2, and around Earth

    Hi, I'm actually a teacher presently undergoing gravitation and circular motion with my students, and ran into a problem I forgot how to think through. I'm trying to explain Newton's cannonball thought process (shoot a cannonball fast enough off a mountain and it will circle the earth), and...
  38. C

    How to find velocity given force and time? (tennis)

    Hey all, so I've got a math project due this weekend and I could seriously use some advice. I am trying to figure out a way to calculate tennis serve speed given a video. I am using this 6000 FPS video here: Assuming the racket string tension to be 50 lbs (222.41N) I used vectors and geometry...
  39. karush

    MHB M2215b.14 Find the limiting velocity

    $\text{14 The velocity of a body of mass $m$ falling from rest of gravity is given by the equation}\\$ \begin{align*}\displaystyle V&=\sqrt{\frac{mg}{k}}\tanh\left[\frac{gk}{m} \right] \end{align*} $\text{$k$ is a constant that depends on the bodys aerodynamic properties \\ and the density...
  40. M

    Kinematics question(angular velocity)

    Homework Statement Question: A circular cylinder with mass of 1 kg and radius a=0.1 m is rotating about its cylindrical axis at a rate of 5 revolutions per second. It is then placed on a flat surface. Assuming that there is no dissipation at contact and the cylinder is rolling without slipping...
  41. M

    I Velocity difference not preserved in special relativity

    Consider single line motion. If an observer sees two objects, and one is seen moving say 50 m/s faster than the other, will all other observers measure the same velocity difference? The answer seems to be 'No' from the velocity addition formula of special relativity? Thus same velocity...
  42. J

    Fluid Velocity and Pressure in a *Closed* System

    In a closed fluidic system (with a pump), fluid velocity is constant throughout the system but what puzzles me is the pressure drop due to viscous effect. In a horizontal pipe, pressure decreases gradually (assuming low friction) down the pipe due to viscous effect. In this concepts, it's hard...
  43. U

    Calculating Diffusion Velocity in Electrochemical System

    Let's suppose an electrochemical system with given coordinates: We are interested in diffusion motion of ion ##i## in the direction of ##y## axis. Concentration ##c_i## is a function of both ##x## and ##y##. Concentration ##c_i## at ##y=0## is zero. The system is steady thus ##\frac{\partial...
  44. W

    Generalized Velocity: Lagrangian

    Homework Statement [/B] In this example, I know that I can define the horizontal contribution of kinetic energy to the ball as ##\frac{1}{2}m(\dot{x} + \dot{X})^2##. In the following example, Mass ##M_{x1}##'s horizontal contribution to KE is defined as ##\frac{1}{2}m(\dot{X} -...
  45. S

    I Velocity addition and conservation of the energy

    Hello everyone, For some time I'm a little bit confused about (at the first view) a very simple question, which is about the conversation of the energy of moving objects (in terms of special relativity). As an example let's talk about firearms. If the mass of the gun M1 is infinitely higher...
  46. S

    Stray/Parasitic Capacitance - Impacts phase velocity?

    Hey everyone, I'm trying to measure the stray capacitance in a circuit comprised of an rf signal generator, an oscilloscope, a coaxial cable (short-circuited) and some capacitors. I measured the resonant frequencies of the coaxil cable for varying values of capacity (0pF to 850pF) between 4MHz...
  47. T

    Calculate the Curl of a Velocity vector field

    Homework Statement The velocity of a solid object rotating about an axis is a field \bar{v} (x,y,z) Show that \bar{\bigtriangledown }\times \bar{v} = 2\,\bar{\omega }, where \bar{\omega } is the angular velocity. Homework Equations 3. The Attempt at a Solution [/B] I tried to use the...
  48. F

    Angular velocity and friction

    Homework Statement A coin stands vertically on a table. It is projected forward (in the plane of itself) with speed v and angular speed w. The coefficient of kinetic friction between the coin and the table is u. What should v and w be so that the coin comes to rest (both translationally and...
  49. flashsnack

    How to calculate velocity based on distance and time?

    Hi everyone, my first of what I can only imagine will be many questions here. I’ve been learning some kinematic equations and have been doing pretty well calculating acceleration. The issue I’m having is this. I found this tutorial...
  50. F

    Understanding Angular Velocity: Exploring Its Direction and Significance

    I’m not quite sure where to put this post so forgive me if it’s misplaced, but can somebody explain why the angular velocity in the picture here appears to be in the opposite direction as I would expect if the velocity is in the direction that is is. I’m not looking to solve this problem...
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