# 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### Graphing velocity, acceleration, and position

im not sure where to start
19. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### 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. ### B Four Velocity Sign of Time: \dot t>0?

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

49. ### 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. ### 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 -...