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. P

    Calculate Earth's escape velocity using different methods

  2. LCSphysicist

    Rocket ejecting mass in a direction perpendicular to its velocity

    That was my approach: $$P_f - P_i = [(m-dm)(v + dv) + dm(u+v+dv)] - [m(v)]$$ $$= mdv - dmv + dmu + dmv = mdv + dmu = 0$$ Since the variation of the rocket's velocity is perpendicular to itself, $$ dv = v d \theta => m v d \theta + dm u = 0$$ So we have $$\frac{dm}{m} = \frac{-v d \theta}{u}$$...
  3. C

    Velocity Formulas for Projectile Motion

    Hi, so I solved this using energy. I also tried solving this using kinematic equations. The issue I am running into s for calculating the Vy of the problem. I am able to find the time it takes the rock to fall using d=(1/2)gt^2. Then, I considered two different ways of going about finding the...
  4. Anmol Dubey

    Calculating final rotational speed from angular velocity

    I have no idea how to go about this. Any help would be appreciated thanks :) Edit: I converted the 1.5 rev/s to rad/s = 9.4 rad/s
  5. Eobardrush

    Ball rolling down a slope problem: Find an expression for time taken

    Question: Galileo released a metal ball from rest so that it could roll down a smooth inclined plane. The time t taken to roll a distance s was measured. He repeated the experiment, each time recording the time taken to travel a different fraction of the distance s. Write an expression for the...
  6. Anmol Dubey

    Finding time taken to stop a skater given mass, velocity and force

    I derived the formula for t but don't know how it works Δt = p/F I got p = mv = 60*8 = 480kgms-1 Δt = 480/120N = 4s Is that correct?
  7. T

    Low pressure, high velocity flow vs static pressure

    In this scenario, we have a compressible flow at 0.99 barA pressure and flowing at 300 m/s velocity and is released into 1 barA pressure. Point is, whether the flow can be released at 1 barA or not at the release pressure is higher than the pressure of the compressible fluid inside the tube. And...
  8. D

    I Solving for Angular Velocity After a Disc Collision

    Hello to everyone, first of all shame on me I has to ask and can not figure out it by myself... The problem is I am trying to code game where two homogenous discs with same mass and same diameter, no fricition due to gravitational forces, can collide. I can figure out the speed and direction...
  9. H

    I Group velocity for an electromagnetic wave inside glass

    Hi, I saw that the group velocity for an electromagnetic wave can be calculate with the following formula ##v_g = v_p + k \frac{d v_p}{dk}## Thus, since ##v_p = \frac{c}{n} = \frac{\omega}{k}## Is it correct to say that ##v_g = \frac{c}{n} + k(- \frac{\omega}{k^2})## where ##k =...
  10. A

    I If we throw a ball with initial velocity v0, is there a force?

    If we throw a ball with initial velocity v0, and the ball progresses in a projectile motion, ignoring air resistance, will there be a force in the x direction? If so, what is that force in the x direction's value mathematically? I know there is a force in the y direction due to gravity.
  11. Zeeshan Ahmad

    Understanding Velocity Transformation

    I have used velocity transformation ibut a little confused on it so do solve the problem
  12. L

    I Interference - two waves of different frequencies - beat velocity

    Hello, I'm considering the "beats" phenomena. I have two plane waves in some medium with a refractive index n(ω), one propagates in a z direction and second in a direction making an angle θ with z axis. Waves have frequencies ω1, ω2 (not necessarily equal) and k-vectors k1, k2 (not necessarily...
  13. J

    Velocity of two masses due to electric potential energy

    We can find the potential energy by finding the potential difference between the two masses. the minimum distance between the two masses is 10 cm. The maximum is 30 cm because they can be 3 string lengths apart as they repulse each other once the string is cut. So, to get potential difference...
  14. A

    How Is Delta_h Calculated in Physics Problems?

    b) My question is here! 0.9v_t = v0 + a*t = a*t t = 0.9v_t/a delta_h = v0*t + 0.5*a*t^2 = 0.5*a*t^2 = 0.5*((0.9*v_t)^2)/a = where a = (-m*g + b*v)/m delta_h = (0.5*((0.9*v_t)^2)*m)/(-m*g + b*v) plugging in everything delta_h = 1.65 m which is not what the answer is. Please help
  15. Anmol Dubey

    Making a Velocity vs Time graph for a bullet

    Here is my working in case it helps :)Ignore the v = 0.6/0.0001 = 6000m/s
  16. P

    Engineering Velocity Decay Curve for a Rocket

    I am trying to solve the problem below. I have previously calculated from 0 to 4 seconds how far the rocket will travel in each second. I am stuck now as to how to start this problem. I have searched but unable to find the answer. Do i need to rearrange this? A is currently 14 which does not get...
  17. J

    Find net velocity of charged particle in electric field (symbols only)

    We know the net force on the charged particle in the uniform electric field pointing up is mg - qE. To get acceleration, divide the net force by mass to get g - qE/m Plug into kinematic equation and get velocity by itself and substitute$$\sqrt{h(2g - \frac{q \sigma}{\epsilon_o m})}$$
  18. Y

    Horizontal velocity of a basketball as it goes through the hoop

    hey i don't understand why my answers are incorrect, here is my solution i would like if someone can help me understand what I am doing worng and how i should solve this problem
  19. Keith Koenig

    B Length, Time, and Velocity -- Which are fundamental quantities?

    We think of length and time as the first fundamental quantities and velocity as the first derived quantity but any two determine the third so we would be completely justified in defining velocity as a fundamental quantity and one of length or time as the other, with the remaining being the first...
  20. rudransh verma

    B Is the final velocity of a Tossed tomato the same as its initial velocity

    When a tomato is thrown up with a velocity ##v_0## it’s kinetic energy is 1/2mv_0^2. It will stop at the top and then again comes back to the launch point where it’s kinetic energy will be same as before, 1/2mv_0^2. How is this possible? Also when we throw the tomato up how can you be so sure...
  21. Y

    The velocity of the particle as a function of time

    this is how i try to solve it: can someone please help me with that because i don't know what I am doing worng here.
  22. V

    Direction of of the velocity vector for particles in a sound wave

    Using the equations mentioned under this question, I came up with following analysis and directions of velocities on either side of ##x_1##. Also, I'm not sure if there is an easier qualitative way to know the velocity directions rather than do a detailed Calculus based analysis?
  23. dirb

    The time for a proton to reach a certain velocity

    A nuclear reactor is built to fuse two hydrogen atoms that are already ionized to protons. However, the electric field of the protons are becoming a significant obstacle. If the reaction was to be defined as H2--> 2H++2e-, if the mass of a proton is mp, the radius of a proton r the charge of an...
  24. dirb

    Calculating Angle & Speed to Reach Planet's Moon from Station Orbit

    A station is orbiting a planet at a distance R1, a moon is orbiting the planet at distance R2 with the period T. The planet itself has a radius rp and a mass mp. We know that when an object adds its velocity at a point in the orbit, the height of the opposite orbit will increase. Determine the...
  25. Physics_learner

    Kinematics - can't find the initial velocity according to the image

    I tried to write the data I understood from the image: y0=160m yf=0 x0=0 x1=192m I tried to express the total change in time using the position over time equation on the Y direction: y(t)=y0+v0y*(t2-t1)-0.5a(t2-t1)^2 but then I stuck with 2 variables and didn't know what to do any help?
  26. crism7

    Calculating Time of Flight & Velocity of a Ball Thrown Upwards

    Vertical components: dy = 0m ay = 9.8m/s^2 [down] t = 1.34s V1y = required V2y = 0 i first tried to find V1y dy =vi t + 1/2 a t^2 and got V1y = -6.566 then i solved for time of flight dy =vi t + 1/2 a t^2 0 = -6.566t + 4/9t^2 and for 1.34 seconds does this mean the time of flight is the...
  27. 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...
  28. 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 =...
  29. 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...
  30. 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...
  31. 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...
  32. P

    B What gives satellites their tangential velocity?

    What gives satellite a tangential velocity?
  33. J

    Velocity, traveling distance and friction force on a sliding object

  34. 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...
  35. J

    What is the relationship between angle and static friction?

  36. 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...
  37. 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:
  38. e2m2a

    Python 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.
  39. 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...
  40. 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...
  41. rudransh verma

    Integration of velocity to get displacement

    Integration of v= integration of##(alpha \sqrt x)dx##. But I am getting wrong answer.
  42. 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
  43. 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...
  44. 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...
  45. 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...
  46. 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.
  47. 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...
  48. 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?
  49. 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...
  50. 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=...
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