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. mazia

    Questions Regarding a Cat Going Up a Ramp

    I've tried a few different ways but each was wrong. At first, I tried solving for acceleration and then using that to solve for final velocity but that was incorrect. I checked the hints given to me by Pearson which tell me to find the total work first, and looking at the hints for that, they...
  2. H

    Change in momentum: Child jumping from a swing on a playground

    800 - (32 x 9.8) = 32v/0.18 where v = velocity this gives me v = 2.736 m/s The answer given, however, is 800 = 32v/0.18, i.e. v = 4.5 m/s The difference, of course, is the weight of the child. I don't understand why this is not allowed for in the net force acting on the child. Can someone put me...
  3. S

    Projectile Motion Problem: Kicking a soccer ball over a fence

    initial velocity y component is (cos30) * 20. t = 25m / ((cos30) * 20)m/s = 1.45 seconds d = vt + .5at^2 v= 20sin30 v= 10 , d= 10(1.45s) + .5(-9.8m/s^s)(1.45s)^2 d=4.2m 4.2-2.5 = +1.7m, so the ball will not hit the fence I need confirmation please
  4. verkamp

    Calculating relative velocity -- Jumping between two moving trains

    is it possible? I've given it quite some thought, and my conclusion was that it would be possible, cuz right after I jump, I'll still have the same velocity in the same direction as the running train?
  5. SwetS

    A Addition of two velocities

    I am going through https://itp.uni-frankfurt.de/~hees/pf-faq/srt.pdf, here I don't understand how we wrote eq. 1.5.3 with the help of three-vectors to get eq. 1.5.4.
  6. yashboi123

    The velocity of a satellite rotating around the Earth

    Not sure what r would be in this scenario. I tried adding the radius of the earth to the altitude but that wasn't correct either.
  7. Lotto

    B What will be the ball's velocity after a perfectly elastic collision?

    From the bus driver's point of view, who is at rest, the ball's initial velocity is ##u+v##. After the collision, its velocity has to have the same value, but an opposite direction, so ##-(u+v)##. So that means that relative to me standing on the ground at rest, the ball's new velocity is...
  8. giodude

    8.01 MIT OCW PS1.4: Throw and Catch (Kinematics)

    1) Using "The person catches the ball at exactly the same height it was thrown from.", we can isolate t by solving yb(t) = v0*sin(theta)*t - (1/2)*g*(t^2) = 0: yb(t) = v0*sin(theta)*t - (1/2)*g*(t^2) = 0 v0*sin(theta)*t = (1/2)*g*(t^2) 2*v0*sin(theta) = g*t t = 2*v0*sin(theta) / g 2) At the...
  9. question_asker

    I Tracing parabolic motion with only current velocity and position?

    Is it possible to trace the trajectory of an object using only its velocity and position, both of which are given as components. My method of doing so involves using the time until max height is reached, and using that time value to calculate the max height itself (h,k), then plugging in the...
  10. S

    Speed of Message Relative to a Space Station: Relativistic Addition

    u is the speed of the message relative to the station v is the speed of the spaceship relative to the station u’ is the speed of the message relative to the spaceship u=(-0.5c+0.7c)/(1+((-0.5c)(0.7c))/c^2 ) =0.2c/0.65=0.308c This just seems way too high, and I'm not sure if I'm doing it...
  11. Slimy0233

    Velocity vs Speed (What's more relevant here?)

    This is a famous book in India. I was wondering if one could say if the answer should include velocity or speed. I mean, I don't think there are any details which hint at velocity. We are gives speed in the question and we are asked to find out the distance traveled, this hints we are asked to...
  12. Amsalja

    7th Grade Asteroid Simulator

    I'm not sure. A source said New Velocity = Current Velocity - TerminalVelocity every second until New Velocity = TerminalVelocity But it doesn't seem right
  13. Slimy0233

    Calculate Distance Traveled: Instantaneous vs. Average Velocity

    edit: I don't know why my latex isn't rendering, any help would be appreciated. Edit 2: The question was due to a misunderstanding I had, I thought integrating instantaneous velocity would give me average velocity. I have attached what I have tried so far. I had a doubt. Can you calculate the...
  14. J

    Velocity and the human experience

    TL;DR Summary: Velocity and the human experience As I was walking into work this morning I looked up and noticed an airplane flying overhead. Airplanes travel at speeds of up to 550 miles per hour while in flight. This question is really less about physics and more about our everyday...
  15. paulb203

    B Velocity of freefalling bodies after 1s, 2s, 3s, etc

    On many websites etc the velocity of a freefalling object in a vacuum is shown as follows. After 1,2,3 and 4 seconds respectively; 9.8m/s; 19.6m/s; 29.4m/s; 39.2m/s I worked out the distance travelled by a freefalling object in a vacuum using d = at^2/2, or, d = 0.5gt^2 and got, for after...
  16. C

    Moving Source, Observer at Rest, derivation for Doppler effect

    For this, Does someone please know whether they assume for the equation highlighted that ##\frac{v}{f} ≥ \frac{v_S}{f}## since otherwise the wavelength would be negative (which I assume is impossible)? Many thanks!
  17. H

    Circular Motion: Tangential and Normal Acceleration

    Hello Physicsforum! This is my attempt: First I realised: ##a_s=a_n## Secondly I used since previus known formulas: ##a_n=\frac {v^2} {R}## ##v=v_0+a_s*t## Although now I do not know how to continue, any suggestions would be appriciated! Thanks for your help on beforehand :smile:
  18. B

    Graphing velocity, acceleration, and position

    im not sure where to start
  19. P

    What is the velocity vector of (rsin(phi), rcos(phi), 1) ?

    I did try to solve the problem by forming the derivative and my result was: v=(rcos(phi), -rsin(phi),0). My solution is wrong, the tutor corrected the task but he didn’t give us the results. My question is what the solution is. Thanks in advance.
  20. A

    Why is the work done double its expected value? (conveyer belt)

    The question was this: My calculations show that the answer should be equal to work done on crate to make it reach the same velocity which is equal to 216 J but the answer given is 432 J It is believed that extra energy is needed to overcome friction but friction is an internal force and...
  21. BadgerBadger92

    B Perception of Velocity in Special Relativity

    If an object is going close to the speed of light, will outside frames of references perceive the moving object as going slow or fast?
  22. A

    Engineering Drawing velocity polygon for a press mechanism

    Hello, I'm new to the forum, I want to ask help on this problem here, above is a press mechanism and I'm tasked to draw a velocity polygon based on this mechanism. The point of contact between the two gears is A and consider it as a swivel hinge (rotating but stay still), so I guess it's O2...
  23. mahdis

    Fluid flow rates in straight vs coiled tubes

    If you have 2 pipes of the same cross sectional area, same volume of fluid, and same length, the only difference is one pipe is coiled several times over a cylindrical object theoretically shortening the length of the pipe, while the other is a straight pipe. Will the flow rate be same in both...
  24. Asem

    Angular Velocity of a Large Pendulum on Earth as seen from the stars

    I don't understand the question. how am I supposed to find the magnitudes and directions of the velocity from the figure?
  25. Mohmmad Maaitah

    Solving a Problem: What Went Wrong & Velocity for Both Masses

    This is the problem: And this the answer provided by the examiner: And this is my own answer: So what did I get wrong??? Also I want to know if the Velocity is the same for both masses.
  26. ahmadphy

    I The effect of a field on a particle depends on the particle velocity?

    Assume there is a force (vector field) on the space .....does the effect of this field on the particle(the change of momentum) at some position depend on the speed at that position? And is it related to the time interval dt the particle experiences this force ? Can i say dt=dx/v? And is that...
  27. P

    I Rolling Motion direction of Velocity center of mass

    Hi I have come across something confusing in rolling motion. If an object moves with a positive V_cm meaning to the right its angular velocity will be clockwise or negative. The formula is V_cm=wR but for a positive V_cm you get a negative w as it moves clockwise if V_cm is to the right...
  28. C

    Average velocity of a particle

    For this, The solution to (a)(i) is 0 ft/s. However I got -4 ft/s. The formula I used was, ##v_{avg} = \frac{s_f - s_i}{t_f - t_i}## ##v_{avg} = \frac{\frac{1}{2}t^2_f - 6t_f + 23 - \frac{1}{2}t^2_i - 6t_i + 23}{t_f - t_i}## ##v_{avg} = \frac{ \frac{1}{2}(t^2_f - t^2_i) - 6(t_f - t_i)}{t_f -...
  29. C

    Finding the velocity of a rock thrown vertically on Mars

    For this problem, The answer is ##6.28 m/s##, however, I got ##-314 m/s## and I am not sure what I have done wrong. My working is, ##H'(t) = \lim_{t \rightarrow 1} \frac{H(t) - H(1)}{t - 1}## ##H'(t) = \lim_{t \rightarrow 1} \frac{-1.86t^2 + 10t -8.14}{t - 1}## ##H'(t) = \lim_{t \rightarrow 1}...
  30. E

    I What is the velocity of a photon through the four dimensions?

    What is the velocity of a photon through the four dimensions? What is the velocity of a photon through the three spatial dimensions x1, x2, x3? What is the velocity of a photon through the fourth dimension x4?
  31. PhysicsNoob2

    Finding max velocity for a kart on a circular, banked track

    This is a UK A-Level question that I'm really struggling with, and can't seem to find any resources online that explain it well. I've been given the following details: mass of gokart + driver = 520kg radius of track = 42m Maximum frictional force between tyres and road on flat track F = 20%...
  32. brochesspro

    I Angular velocity of a rod and what formula to use while solving.

    The question is: A uniform rod of length ##L## stands vertically upright on a smooth floor in a position of unstable equilibrium. The rod is then given a small displacement at the top and tips over. What is the rod's angular velocity when it makes an angle of 30 degrees with the floor, assuming...
  33. Onyx

    B Four Velocity Sign of Time: \dot t>0?

    Is it generally the case even with light like paths that ##\dot t>0##?
  34. brochesspro

    The final velocity of a ball rolling while slipping.

    Here is the problem statement along with the figure. Here, I take the right-ward and anti-clockwise directions to be positive. After the ball collides with the wall, its angular velocity remains the same and its velocity changes direction while remaining the same in magnitude. Using the...
  35. jselms99

    Time Travel: Calculating Velocity for 10 Year Trip

    So at first I thought that the time would be 10 years, and that I’d have to consider the outbound motion as v = .87c and inbound motion as v = -.87c but I’m struggling with addition of the velocities and whether or not this is even the right approach?
  36. M

    Kinematics : Average velocity problem

    The car covers half of the road with an average velocity of v, so the elapsed time is equal to: ##t_1=\frac {d/2} {v}=\frac {d} {2v}## And it covers 1/4 of the road with an average velocity of 2v, so the elapsed time is equal to: ##t_2=\frac {d/4} {2v}=\frac {d} {8v}## Then it covers 1/8 of the...
  37. A

    Final velocity involving a can of soup and an inclined plane

    a = 9.8*sin(25*pi/180)=>a=4.1417 m/s^2 vf^2=vi^2+2*a*s=>vf=sqrt(0^2+2*4.1417*3)=>vf=4.9850 m/s Meanwhile the correct answer is: (vf+vi)/2=>(vf+0)/2=2=>vf=4 m/s Why is my answer wrong? It seems that the acceleration is what is wrong, but I don't understand why.
  38. monsterhart

    1D Particle & Energy w/ F(x): Am I doing this right?

    A) I just did what it said to do: $$\sin\left(4x_{1}\right)=1\implies x_{1}=\frac{\arcsin\left(1\right)}{4}\ m=\frac{\pi}{8}\ m\approx 0.392699081699\ m$$ B) I modified the method from an example from the lecture the other week: $$U\left(x\right)=-\int...
  39. brotherbobby

    The gravitating of a small mass towards a big mass

    Diagram : I draw a picture of the problem situation and paste it to the right. Attempt : Let me assume that the position of the smaller mass ##m## at a given instant of time ##t## is ##x(t)##. (1) Gravitational potential energy ##\frac{GMm}{x} = \frac{1}{2}mv^2(x)##, where ##v(x)## is the...
  40. E

    How to calculate Earth speed of the Moon induced orbit?

    It didn't work and I don't know how to do it.
  41. E

    I Velocity of Buoyant Plug in Closed Loop

    A problem I was thinking about when talking about natural circulation in a closed loop in another thread: What is the velocity of the buoyant plug? The loop is filled with water. There are no viscous forces acting on the plug or in the flow. The flow is assumed incompressible. 1) Is the...
  42. T

    A Need help with an integral -- How to integrate velocity squared?

    The integral is this one: ##\int (\dot x)^2 \, dt,## With ##x=x(t). ## I don't know how to solve that integral and I haven't find nothing to read about on how to proceed with this kind of (implicit function?) integrals without having the initial function.
  43. Asem

    Find Initial Velocity of a projectile given flight time and angle

    Vix=Vcosθ Vix=0.76604*V Xf=Vixt Xf=0.77604V*2 V=Xf/1.55208
  44. Sciencemaster

    I Gravitational Field Transformations Under Boosted Velocity

    Let's say we have some observer in some curved spacetime, and we have another observer moving relative to them with some velocity ##v## that is a significant fraction of ##c##. How would coordinates in this curved spacetime change between the two reference frames? For example, imagine a...
  45. L

    Finding the terminal velocity of a model rocket from a list of velocities

    Ok, i have some rocket data from a 20,000 foot launch. I have the times, altitudes, and velocity at said time. Is it possible to find the terminal velocity from this long list of numbers? I tried graphing the velocities to see where the curve flattens out, since usually that is where terminal...
  46. Clockclocle

    I When does the instantaneous velocity exist?

    The instantaneous velocity at time a is defined as derivative of motion function f(t). It is not similar to average velocity in an interval of time. From the Newton law. If an object is at rest, we must exert a force to make it move, assume that there is no friction. Depend on the weight of...
  47. brotherbobby

    B In uniform acceleration, mean velocity ##\bar v = \frac{v_0+v}{2}##?

    Question : For uniformly accelerated motion ##a(t)=a_0\;\; \forall \text{times}\;t##, we can say that the average velocity for the entire motion ##\bar v = \frac{v_0+v}{2}##, where ##v(t)## is the final velocity at some time ##t## and ##v_0## is the initial velocity. How do we show that? Issue...
  48. paulimerci

    Find the final velocity of the bobsled after the last bobsledder jumps in

    For calculating the total impulse, I'm taking the individual impact force times the elapsed time and adding them all together to get the total impulse. Given F = 25N, ## \Delta t_1 =3 secs##, ##\Delta t_2 = 4secs##, ## \Delta t_3 = 5secs##, ## \Delta t_4 = 6secs##. $$ Impulse 1 = F \Delta t_1 $$...
  49. paulimerci

    A or B? Increase in Velocity Backwards & Acceleration Forward

    I've understood that between time t=0 to t=1 sec (moving backward), the object is moving with increasing velocity in the negative direction, slows down, and comes to rest at t = 1 sec. At t = 1 sec, the object returns to its starting position, briefly rests, and then begins to accelerate (moving...
  50. A

    Finding velocity for projectile given distances and launch angle

    i used t=d/v for the x direction using the formula t=250/vcos55 and subbed that into the formula for the y direction d = (v) (t) + (0.5) (a) (t)^2 35 = (vsin55) (250/vcos55) - (4.9) (250/vcos55)^2 canceled out the first two v 35 = sin55 (250/cos55) - (306250/v^2cos3025) 35 = 357 -...