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. G

    I Velocity in Relativity: Theoretical Analysis of Multi-Dimensional Universes

    There are several theoretical analyses of 2 dimensional or of multi-dimensional universes. Now, we live in a special universe that follows Newton's first law (A body at rest or a body in motion shall continue to be at rest or in motion till acted upon by an external force), and consequently...
  2. Istiak

    Calculating Velocity when Stuntman Jumps from 1.25m Height

    > >A stuntman jumped from $1.25 \ \text{m}$ height and, landed at distance $10 \ \text{m}$. Find velocity when he jumped. (Take $\text{g}=10 \ ms^{-2}$) I had solved it following way. $$h=\frac{1}{2}gt^2$$ $$=>1.25=5\cdot t^2$$ $$=>t=\frac{1}{2}$$ And, $$s=vt$$ $$v=\frac{s}{t}$$ $$=\frac{10 \...
  3. A

    B Why Is Initial Velocity Not Always Zero?

    There is something I don't understand. Isn't every object, if thrown, the initial velocity is zero? Please take a look at below example. Why the initial velocity in the below example is 98 ms^-1? Please explain. I also would like to ask what textbook contain a lot of basic physics example for...
  4. Huzaifa

    B Acceleration of Moving Particles: Explained

    I am not able to understand the following paragraph from my Physics textbook;
  5. Marwan1303

    I Pipe Air Blowing - Exit Velocity of Air

    Suppose an isolated pipeline of known dimensions is being filled with air from the atmosphere (via a compressor) to a gauge pressure P1=2barg. A rupture disc at one end of the pipeline blows at this pressure, and the air inside the pressurized pipeline is released to the atmosphere. The rupture...
  6. karush

    MHB When Will the Object Be 15 Meters Above the Ground?

    $\tiny{1.2.1}$ An object is propelled vertically upward with an initial velocity of 20 meters per second. The distance s (in meters) of the object from the ground after t seconds is $s=-4.9t^2+20t$ (a) When will the object be 15 meters above the ground? $15=-4.9t^2+20 \implies -4.9t^2 =-5$ ok...
  7. WMDhamnekar

    MHB What Is the Actual Velocity of Wind?

    My attempt to answer this question: Let the actual velocity of wind is $\vec{v}=x\hat{i} + y\hat{j}$ where $\hat{i}$ and $\hat{j} $ represents velocities of 1KM per hour towards east and north respectively. As the person is going northeast with a velocity of 6KM/hr, his actual velocity is $...
  8. baby_1

    Phase velocity in oblique Angle propagation (Plane wave)

    Hello, Regarding the wave oblique angle propagation and based on Balanis "Advanced engineering Electromagnetic" book on page 136 ( it has been attached) I need to know why the phase velocity in x direction is not important to keep in step with a constant phase plane( Just equation 4-23). I...
  9. WMDhamnekar

    MHB Understanding Velocity and Acceleration of a Moving Particle

    A particle moves so that its position vector is given by $\vec{r}=\cos{(\omega t)}\hat{i} + \sin{(\omega t)}\hat{j}$. Show that the velocity $\vec{v}$ of the particle is perpendicular to $\vec{r}$ and $\vec{r} \times \vec{v}$ is a constant vector. How to answer this question?
  10. WMDhamnekar

    MHB Question on velocity and acceleration

    How to answer this question? Any math help, hint, or even correct answer will be accepted.
  11. WMDhamnekar

    MHB Velocity and acceleration vectors and their magnitudes

    How to answer this question? I am working on this question. Any math help, hint or even correct answer will be accepted.
  12. Ashshahril

    How to Visualize a 4 vector (e.g. a velocity)?

    Velocity is a 4-vector which has 3 space dimensions and 1 time dimension. It's space parts will be directed at the 3 space directions and time parts will be directed at the time dimension (But it is inverse. So, will it point at the inverse direction?). How can someone Visualize it? How they...
  13. Huzaifa

    B Average Speed vs. Velocity: Explained

    Though average speed over a finite interval of time is greater or equal to the magnitude of the average velocity, Instantaneous speed at an instant is equal to the magnitude of the instantaneous velocity at that instant. Why so?
  14. E

    Can you use speed and velocity interchangeably?

  15. E

    When an object is accelerating, does speed, velocity, or force change?

    qn3: why is statement 2 the only answer? isn't speed one of the factors in velocity too? then shouldn't statement 1 be true too?
  16. K

    A Can high air velocity in vacuum system create "freezing" of the pipe?

    Hi folks, very simple question, but have not been able to find an answer: Assume a vacuum pump pulls air through a pipe. Also assume that within the pipe run, there is an area with reduced cross section, creating a temporary increase in air velocity. Also assume the air is very moist, and is at...
  17. E

    How Does Vorticity Relate to Blood Flow Dynamics?

    This is not homework. I'm studying fluid mechanics/dynamics in the heart/blood vessels and I just want to understand this, so I can have a better appreciation for it's clinical relevance. I'm more of biology/biochem type of person so this has been a bit of challenge. I have basic physics course...
  18. WMDhamnekar

    MHB What is the velocity vector after a pinball bounces off a baffle?

    Hi, A pinball moving in a plane with velocity s bounces (in a purely elastic impact) from a baffle whose endpoints are p and q. What is the velocity vector after the bounce? I don't understand how to answer this question? Any math help, hint or even correct answer will be accepted?
  19. B

    What is the perceived relative velocity of these two motorcycles?

    I tried to project one on top of another but I know that's incorrect since I don't know how of do this.
  20. Andy Resnick

    I Apparent angular velocity (inclined orbit)?

    Here's the problem setup, my student and I are stuck. A disk is rotating at constant angular velocity ω, and we are watching a point on the rim, parameterized by the angular position θ, move. Because we are observing the motion from an inclination angle Ψ, we do not always observe the...
  21. S

    Calculation of orbital velocity -- Geometrical solution

    Hello, I would like to calculate the orbital velocity using the geometrical way of reasoning. But I have a hard time to understand and apply some basics into my calculations. The reasoning is pretty simple. After some time: dt ,the particle travels the distance: Vtot1 * dt = R*sinθ (see the...
  22. S

    Why is the integrated velocity times change in velocity zero?

    So consider a subject system, a galaxy, with stars in it. This galaxy is passed by another object, the perturber. When the interaction is fast, we call this interaction a high-speed encounter. Now we consider that the interaction is really fast. This means that during the interaction, the...
  23. S

    Hurricane forces — Comparing the force from a 60 mph wind to a 120 mph wind

    The marker wrote that the answer is 4 and it's because m and v double. I don't understand how m doubles??
  24. B

    Existential dilemma on angular velocity of a complex rigid body

    I assumed the angular velocity of the center of mass of the two discs about z axis to be w1 note that angular velocity of center of mass of both discs and center of anyone disc about z axis is same, you can verify that if you want, me after verifying it will use it to decrease the length of the...
  25. G

    Vectors - Aircraft's velocity relative to ground

    I attach my working below - my angle is correct according to mark scheme but magnitude isn't (should be 230). I think it's odd that my resultant velocity on a windy day is larger than velocity in still air, but apparently my angle is correct? I've been told that I've calculated the airspeed it...
  26. ILoveParticlePhysics

    Why do things with wheels get more balanced as velocity increases?

    You can try this at home!
  27. P

    Lagrangian mechanics - rotating rod

    Hello, It might sound silly, but when I try to calculate the kinetic energy of a rotating rod to form the Langrangian (and in general), why it has both translational and rotational kinetic energy? Is it because when I consider the moment of Inertia about the centre I need to include the...
  28. nick26

    Measure angular velocity and acceleration from missing tooth wheel

    Hi, I need to come up with a math model for a digital ignition system. I've been thinking about it and I think that I need to measure 2 things to be able to calculate when I have to start charging the coil. They are the angular velocity and the acceleration but how can I do it? the idea is to...
  29. A

    Milky Way Velocity: How Fast Does Our Galaxy Move?

    Do we know at which speed the whole milky way is moving around in the universe? Around the next cluster I suppose?
  30. T

    Blower fitted with a velocity stack

    Many of us know about velocity stacks. It's a proven fact that velocity stacks can enhance the performance of internal combustion piston-cylinder engines. I want to know if a velocity stack is added at the upstream (just before) to a blower/fan, whether it can enhance the performance of the...
  31. A

    I Recession Velocity near Cosmological Boundary: Hubble's Law?

    I'm confused whether Hubble's Law applies to objects near the cosmological horizon (CH). I'm told that objects asymptotically approach the CH and freeze there (v -> 0) in the same way that occurs during in-fall towards a black hole. But Hubble's Law says that velocity is proportional to...
  32. Kairos

    B Misuse of Velocity Addition: Troubleshooting

    Something seems wrong with my use of velocity addition: A fly of rest mass ## m_{0} ## in your reference frame (say a platform) is posed in a train passing with a velocity ## v ## relative to the platform. The fly mass is now for you ## m_{1} = m_{0} \gamma(v) ##. Now in the train the fly is...
  33. Advay

    Terminal angular velocity of Disc in magnetic field

    Torque appiled by smaller disc = mga emf of disc due to B = Bwr2/2 Current I = Bwr2/2R force = IBr = Bwr3/2r torque = rF = Bwr4/2r mga = Bwr4/2r
  34. V

    How to determine angular velocity about a certain axis?

    If the crawling insect were stationary at a certain instant of time, then it would have the same angular velocity as that of disk, which is w in a clockwise direction. But now it's velocity at any instant is the vector sum of velocity due to rotation and the velocity it crawls at. My attempt is...
  35. brotherbobby

    Projectile motion with (constant) wind velocity

    Let me start be making a small sketch of the problem, shown to the right. If the range of the projectile on a still day ##R = v_{0x}T##, then on the windy day the range becomes ##R+2H = v'_{0x}T = (v_{0x}+v_w) T##. Since the maximum height attained by the projectile ##H =...
  36. 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...
  37. 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?
  38. 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...
  39. 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...
  40. 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...
  41. 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?
  42. 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...
  43. 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...
  44. 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...
  45. 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...
  46. 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.
  47. 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...
  48. 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
  49. 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.
  50. 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...
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