Velocity Definition and 1000 Threads

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. L

    Relative velocity of exhaust in Ideal Rocket Equation

    In this derivation of the Ideal Rocket Equation (https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation#Most_popular_derivation), they use the fact that ##V_e = V - v_e##, or that the velocity of the exhaust in the observer frame ##V_e## is the velocity of the rocket ##V## minus the speed of...
  2. K

    Calculating Velocity of Water Flow in Open Channel

    Homework Statement [/B] We have water flowing in an open channel. A small tube is placed in the channel, and the water raises to a height "l" above the water surface. The distance from the water surface to point 1/2 (points are at same height) is d. At point 1 the fluid velocity is V1 and at...
  3. Lucw

    Escape velocity when the rocket's mass is not small compared to the asteroid

    Hello When one calculates the speed of liberation of an object with respect to a star, one takes into account the force exerted by the star on the object. But not the force exerted by the object on the star. For small objects, this is valid. But what is the speed of release of a 1000 kg rocket...
  4. T

    Angular velocity inside a vortex tube

    I hope many here know about vortex tube and its application. I myself have done some study but were unable to find one answer. If we know the speed of the inlet fluid, then how can the angular velocity of the fluid during its rotational motion can be determined.
  5. Lukeblackhill

    Measuring Velocity of a Sphere - Impulse & Energy Conservation

    Morning! I was performing some experiments about impulse and conservation of mechanical energy, and for that I was looking to good ways of measuring the velocity of a sphere under the action of a force. In free fall, having the height H it was falling along, I have used the formula v =...
  6. J

    Evidence that the ship had its engine turned on

    Homework Statement Homework Equations a = v/t p=mv(?) The Attempt at a Solution If an engine is turned on, that means that the ships are accelerating since the engine pushes back on air with a force and air pushes back to propel the ships forward, so I thought (A) would be the answer, even...
  7. R

    What is the velocity of the block pulled by strings

    Homework Statement :[/B]In the arrangement shown in the figure, the two ends P and Q of the light unstrechable string move downward with uniform speed u as shown. The upward speed of the mass m is v. Then which of the following is correct: A) v cos60°=u B) 2v cos60=u C) v =2ucos60 D) v= u...
  8. I

    A Calculating Distance from Hand Movements in Surgical Procedures

    I'm a surgeon, maths and physics study was a long time ago. I have been working on a project using an accelerometer and gyroscope.to.monitor hand movements during practice procedures. I thought to represent my 3 axis acceleration as a vector and then subtract from this 1g, to compensate for...
  9. Arka sarkar

    Longitudinal Wave Velocity: Why it's Greater in Solids

    Why the velocity of longitudinal wave in solid is greater than transverse wave
  10. E

    How kinetic energy is proportional to velocity squared

    I hear somewhere explanation why kinetic energy is proportional to $v^2$ and not to $v^3$, for instance. https://www.physicsforums.com/threads/quadratic-forms-and-kinetic-energy.826884/ I wish to find reference for this. Now I find your thread with the same question and very similar answers...
  11. steven george

    Average velocity of gas molecules in a container

    Homework Statement An ideal gas with molecules of mass m is contained in a cube with sides of area A. The pressure exerted by the gas on the top of the cube is P, and N molecules hit the top of the cube in a time Δt. What is the average vertical component of the velocity of the gas...
  12. M

    How can i calculate the velocity in a wind tunnel

    Ive done some wind tunnel experiments for a wing design i made, the wind tunnel was set to 50% power and the incidence angle was increased from -2 to 14 at 2 deg increments, how do i calculate the velocity for each recording? I've done this before but I am just having a mental block on...
  13. Andy Bloch

    I Momentum w/o Net Velocity? Exploring the Lorentz Factor

    (I hope this post doesn't cross the border into the forbidden realm of quackery and speculation.) I have what seems like a simple question about Special Relativity but I haven’t seen it discussed anywhere, nor has anyone I've asked. Does the nonlinearity of the Lorentz factor provide a way...
  14. N

    Velocity of a charged particle as it approaches infinity

    Homework Statement Homework Equations F = k(q1q1/r^2) K = (mv^2)/2 The Attempt at a Solution I got number 18 easy enough, number 19 seems simple but I'm not getting the right answer. I'm calculating Force exerted by each charge on the new charge using F = k(q1q1/r^2) for the three charges...
  15. P

    Differences in velocity conceptual question

    Homework Statement If I want to find the difference in velocities of 2 objects A and B We know the sum of their velocities is A + B But but is the difference B - A Why not A - B? Homework Equations This is from the equation of calculating restitution where (greek letter) = (The difference in...
  16. Hamza Abbasi

    How Fast Does Spaceship A Move Relative to Spaceship B?

    Homework Statement Two spaceships pass each other. Spaceship A moves relative to nearby planet at velocity v1 , while spaceship B moves at velocity v2 relative to the planet . How fast does spaceship A moves relative to spaceship B. Homework Equations Velocity Transformation : v* =...
  17. Gabriel Ulisses

    B How absurd are these numbers really?

    I stumbled upon these numbers on my test recently. It is raelly basic stuff, but i want to know, what would actually happen if such thing happened in the real world. We basically have a ball made of 20Kg of "person". And it it accelerates at 1.8*10^5 m/s² for 1/30 of a second reaching 6000 m/s...
  18. V

    Find the velocity when the ball rolls without slipping

    Homework Statement A thin spherical shell is sliding with velocity ##v_0## on a table initial until friction eventually causes it to roll without slipping. Find its translational velocity when the it rolls without slipping as a fraction of ##v_0##. Homework Equations $$I=\frac{2}{3}MR^2$$...
  19. BookWei

    Velocity is a vector in Newtonian mechanics

    I studied the vector analysis in Arfken and Weber's textbook : Mathematical Methods for Physicists 5th edition. In this book they give the definition of vectors in N dimensions as the following: The set of ##N## quantities ##V_{j}## is said to be the components of an N-dimensional vector ##V##...
  20. T

    Butanol at a temperature of 28 C is pumped at a velocity of....

    Homework Statement Butanol at a temperature of 28 C is pumped at a velocity of 14 m s-1 through a 100 mm diameter tube kept at a wall temperature of 90°C. The properties of butanol are given below. Determine the convective heat transfer coefficient (you will find the appropriate correlation...
  21. Suyash Singh

    Force on conductor in magnetic field

    Homework Statement Homework Equations Emf=B l V V is (velocity) F=QVB The Attempt at a Solution Emf=BLV Work=QBLV Force=BLV how come V=Q/m. its not possible or is it?
  22. N

    I Drift velocity in P-N Junctions

    When a P-N junction is in reverse bias, the drift velocity of the system increases, so why is there no current flow? Is the drift velocity not connected to the current? Thanks in advance.
  23. Muhammad Danish

    Relationship between Velocity and Acceleration

    When the driver applies brakes its velocity starts decreasing and direction of acceleration will be same to the direction of velocity. Is this statement True of False? Please explain the true concept of this scenario. As far as I understand is that Velocity will start decreasing. But I am...
  24. Theia

    MHB Max Horizontal Displacement of Projectile and its Velocity at T

    Let x = v_0\cos \alpha _0 t and y = y_0 + v_0 \sin \alpha _0 t - \tfrac{1}{2} gt^2, where v_0 is speed at time t = 0, \alpha _0 is the angle between positive x-axis and initial velocity vector (\alpha _0 \in (0, \pi/2)), t time in seconds, y_0 >0 the y coordinate at time t=0, g acceleration...
  25. Q

    Independence of Position and Velocity in Lagrangian Mechanics

    In Lagrangian mechanics, both q(t) and dq/dt are treated as independent parameters. Similarly, in Hamiltonian mechanics q and p are treated as independent. How is this justified, considering you can derive the generalized velocity from the q(t) by just taking a time derivative. Does it have...
  26. N

    Velocity of a football with and without drag

    Homework Statement A professional thrower projects a football straight up in the air. 1. Assuming there is no air drag on the football, find the speed of the football as a function of height as the ball goes up. 2. Assuming the air drag on the football varies linearly with speed, find the speed...
  27. S

    Calculating a push force using area, speed, and density?

    Homework Statement The doorway in the previous question measures 1.06 m x 2.04 m, and the wind blows parallel to the wall surface at 3.89 m.s-1. Calculate the force pushing the curtains out of the doorway. The density of air is 1.29 kg.m-3. Known data: A = (1.06m)(2.04m) = 2.162 m^2 v(wind)...
  28. M

    I How do we measure the velocity of stars in a galaxy?

    I have read somewhere that the parallax method can be used to measure the distance to stars up to 400 light years away. I did a quick calculation and estimated that it means that our telescopes can resolve an angular movement of 8.15x10-3 arc seconds. Taking the distance between the sun and the...
  29. Jan Nebec

    B Understanding Resistance of Acceleration: Velocity & Force

    Hello! Why does resistance to acceleration depend on both the velocity of the object as well as the direction of the force? In circular motion, we can measure the centripetal force and centripetal acceleration, then we can calculate objects mass. Speed remains constant. But we would get the...
  30. MIIF

    Is it possible to find dy given the values of dx and v?

    Homework Statement This isn't really a homework problem/question. I am just wondering if it is possible to calculate the vertical distance (dy) when the only given values are those of the horizontal distance (dx) and velocity (v). An example of this projectile-motion problem would be this: A...
  31. A

    Finding initial velocity of two elementary particles

    <Moderator's note: Moved from a technical forum and thus no template.> I'm not sure how they got the extra (1/2)mv^2? My question is shown using pink font in the image below as well as my attempt.
  32. Jan Nebec

    B Gravitational Mass & Velocity: Is There a Correlation?

    Hello! The equation for relativistic mass by special relativity tells us the relativistic mass for object in motion...but since inertia mass has same value as gravitational, does this formula also apply for gravitational mass? Thank you!
  33. Alexanddros81

    Motion of a particle and zero velocity

    Homework Statement 11.7 The motion of a particle is defined by the relation ##x = 2t^3 - 15t^2 + 24t + 4 where x is expressedin meters and t in seconds. Determine (a) when the velocity zero , (b) the position and the total distance traveled when the acceleration is zero Homework EquationsThe...
  34. Alexanddros81

    A loaded railroad car is rolling at a constant velocity

    Homework Statement A loaded railroad car is rolling at a constant velocity when it couples with a spring and dashpot bumber system. After the coupling, the motion of the car is defined by the relation ##x = 60e^{-4.8t} sin16t##, where x and t are expressed in millimeters and seconds...
  35. Jan Berkhout

    Having trouble working out centripetal force?

    Homework Statement The Russian Mir space station had a mass of 130 tonnes and orbited Earth at an altitude of 480km with an orbital speed of 7621.4m/s. The diameter of Earth is 12 760 km. a) What centripetal force was acting on it? b) Find the value of the acceleration due to...
  36. Phantoful

    Bead on a string, find y(x) if horizontal velocity is const.

    Homework Statement Homework Equations K = (1/2)mv2 U = mgh W=Fd Integration/Calculus The Attempt at a Solution I'm not sure what I should be doing for this question, if height changes how is it possible that velocity stays the same, according to the conservation of energy (frictionless wire)...
  37. N

    Maximum Velocity for different accelerations

    Homework Statement Force of jet= A(r(t))4/3 A: constant determined by the fighter model in the class being considered and the drag force on the plane r(t): the rate of fuel consumption as a function of time Consider 3 possible situations for r(t): 1. when the rate is constant for the...
  38. N

    Finding velocity with constant, incre., decrea, varying acce

    Homework Statement Force of jet= A(r(t))4/3 A: constant determined by the fighter model in the class being considered and the drag force on the plane r(t): the rate of fuel consumption as a function of time Consider 3 possible situations for r(t): 1. when the rate is constant for the...
  39. T

    Velocity in polar coordinates (again)

    Hey people, this question was already asked here [https://www.physicsforums.com/threads/velocity-in-plane-polar-coordinates.795749/], but I just couldn't understand the answer given, so I was wondering if some of you could help me by explaining it again. I don't really get Equation (or...
  40. Francis Perez

    Find the Initial Velocity and Launch Angle for a Particular Trajectory

    Homework Statement Hello, so I’ve been trying to find some possible way to calculate this: The initial Velocity and angle needed to launch a projectile and reach the coordinates (x,y). The maximum height the ball can reach before it starts to head down to the target value should be y+5m The...
  41. phantom lancer

    Physics Word Problem: Arrow and moving target collision

    Homework Statement Find the 2 unknown variables.[/B]Homework Equations Am I doing this right? Can someone help me find the solution?[/B] The Attempt at a Solution To compute for the velocity of the target/arrow combination immediately after the collision: M_bV_{bi}=M_bV_{bf}+M_wV_{wf}...
  42. K

    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...
  43. F

    B Third Cosmic Velocity: Will Voyagers Leave Solar System?

    The voyager probes have currently a speed of ##38,000\text{ mph }## which is roughly ##17\text{ km/s }##. Now the third cosmic velocity is ##42 \text{ km/s }## which is far more, and Voyager 2 is even slower. So will they actually leave the solar system, or will they simply orbit in quite big...
  44. Monoxdifly

    MHB [ASK] How much velocity is needed for the rock to be able to hit that bird?

    A bird is located at the (50, 8 ) m coordinate. A boy shot a rock at it using a slingshot with the elevation angle 37^{\circ}. How much velocity is needed for the rock to be able to hit that bird? I substituted all known variables (including the gravity acceleration 10m/s^2, with...
  45. Monoxdifly

    MHB [ASK] Determine its velocity and direction after √(3)/2 seconds

    Something was thrown with an elevation angle 60^{\circ}. Determine its velocity and direction after: a. \frac{1}{2}\sqrt3 second b. \sqrt3 second I tried solving the (a) question by substituting the angle to the equation y=v_0\sin\alpha t-\frac{1}{2}gt^2 and got 0 (the book uses 10m/s^2 as the...
  46. P

    Force decreased but velocity continues to increase

    Homework Statement An object is moving to the right in a straight line. The net force acting on the object is also directed to the right, but the magnitude of the force is decreasing with time. What happens to the object? The answer states that the object continues to move to the right with...
  47. Fia Ismi Nur Alfiah

    How to Determine Velocity and Acceleration from Position?

    Homework Statement [/B] The position of a particle as a function of time is given by r(t) = i(1 - e^-kt ) + je^kt where k is a positive constant. Find the velocity and acceleration of the particle. Sketch its trajectory. Homework Equations v (t) = dr/dt a(t) = dv/dt The Attempt at a Solution...
  48. Philip Dhingra

    I Understanding Length Contraction: What is Limit of Vanishing Transport Velocity?

    I'm trying to understand length contraction from wikipedia, and they mention clock synchronization: The observer installs a row of clocks that either are synchronized a) by exchanging light signals according to the Poincaré-Einstein synchronization, or b) by "slow clock transport", that is, one...
  49. R

    Lift and screw impact velocity

    Homework Statement Consider the elevator and screw in Example 2-17. Assume the velocity of the elevator is 16 mls upward when the screw separates from the ceiling. (a) How far does the elevator rise while the screw is falling? How far does the screw fall? . I have only problem second part of...
  50. S

    Torque required to move a wheeled weight

    I have a problem where I have a large mass on wheels that I want to power with an electric motor. My hope is that I can find the torque i need to start and drive the motor and this is what I have so far. Mass = 400t. Initial velocity = 0 Final velocity = 2.5m/s Distance required to travel =...
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