# What is Velocity vector: Definition and 99 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.

View More On Wikipedia.org
1. ### Elliptical motion in polar coordinates

I think I have completed the exercise but since I have seldom used polar coordinates I would be grateful if someone would check out my work and tell me if I have done everything correctly. Thanks. My solution follows. Since ##\left(\frac{x}{a}\right)^2+\left(\frac{y}{b}\right)^2=1## it follows...
2. ### Solving a Celestial Mechanics Task with Velocity Vector Scattering

Hi, the task is as follows Unfortunately, I am not getting anywhere at all with task c. I have now proceeded as follows: I assume that the calculation takes place in the reference system of the sun. In the task the following is valid, $$\vec{v}_{si}=-s\vec{v}_p$$ I have now simply assumed...
3. ### Determine vertical velocity vector on sloped surface

A golf is launched at a speed v,f and launch angle, β,f. The slope of the green is equal to φ. At some point the ball is located on the rim of a hole. The side view (a) and overhead view (b) looks as in the attached image.According to the author of the [paper][2] "The Physics of Putting" the...
4. ### I Is the Killer Crate Paradox Resolved?

Hi Physics Forums, I've devised a thought experiment called the "Killer Crate Paradox" to put a spotlight on an issue I'm having, with regards to understanding length contraction, specifically in instances where multiple objects are observable and they have different velocities and directions...
5. ### 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?
6. ### Velocity vector addition problem

Hello, guys. Interesting riddle here. I have no idea how to solve it. Tried different methods, but point is answer is always wrong, exact answer Downriver, at an angle of 53.13(degree) to the bank. That exercise is from "Pohl’s Introduction to Physics"
7. ### 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?
8. ### Prove that the derivative of the position vector equals the velocity vector

1.)##\dot{\vec{r}}=\dot{x}\hat{i}+\dot{y}\hat{j}+\dot{z}\hat{k}=\dot{r}\hat{r}## since the unit vector is constant 2.) ##\dot{r}\hat{r}=\frac{x\hat{i}+y\hat{j}+z\hat{k}}{\sqrt{x^2+y^2+z^2}}\frac{\dot{x}x+\dot{y}y+\dot{z}z}{\sqrt{x^2+y^2+z^2}}##...
9. ### Calculating Velocity Vector of Object in 2D Space

The question I am trying to solve is what is the velocity vector (direction and magnitude) of an object in 2 d space. We know the distance measured to the car from two different angles. We know the radial velocity of the car on both measurements. The radial velocity is the component of the...
10. ### Finding time from a velocity vector

I've looked it up online and someone did t=40−65=0.15(h) I was just wondering why they would subtract the velocities. Could something explain this to me please? thanks.

12. ### Mechanics: Angular Velocity Vector Questions

Answers are the following : (i) v=(2cost)i - (2sint)j -(1/2)k (ii)2.06m/s (iii)2m/s^2 horizontally towards the vertical axis, making an angle of pi/4 with both the I and j axes.
13. ### I Four Velocity Vector: why divide by time according to the particle?

So I understand that time is now part of the four vector, and so dividing delta X by delta t (time according to me), would produce just c as the first dimension of the vector, which gives us no intuition as to how fast time is moving for the observer, so is not useful. I understand why we...
14. ### I Velocity Vector Transformation from Cartesian to Spherical Coordinates

Hi all, I can't find a single thing online that translates a cartesian velocity vector directly to spherical vector coordinate system. If I am given a cartesian point in space with a cartesian vector velocity and I want to convert it straight to spherical coordinates without the extra steps of...
15. ### B Measurement of an unknown velocity vector of a closed space

Hi I found this paper on the measurement of unknown velocity vector of a closed space. Does it mean that it is possible to measure the unknown velocity vector of a closed space ? Can someone explain it to me

46. ### What is the Effect of Motion on the Velocity Vector of Light?

Hi, Consider a source of light transmitting light at an angle θ with x-axis as seen in the following figure: Now an observer looking at x-axis will determine the speed of light to be c.cos θ, and the one looking at y-axis determine c.sin θ. How can we resolve this according to the...
47. ### Velocity Vector in Polar Coordinates (Kleppner p.30)

In polar coordinates we have \vec{r} = r \hat{r} \Rightarrow \vec{v} = \frac{d}{dt}({r \hat{r}}) = \dot{r}\hat{r} + r \frac{d \hat{r}}{dt} . In the book Introduction to Mechanics, K & K says the right term is the component of velocity directed radially outward. (Surely a typo, as the left...
48. ### How do you connect angular velocity vector with the positions?

I've been working out a question about rigid body rotations, and though I can grasp the basic math, I'm completely lost about the physical quantities. In particular, I'm trying to relate the three components of the angular velocity vector that I found with the physical picture: Suppose that...
49. ### Speed and direction of Velocity Vector - Inelastic

Homework Statement A 55kg man is running in the positive y direction at 4 m/s. He is tackled by a 115kg man running 8.5 m/s at a 140 degree angle. What is the speed and direction after the inelastic collision? Homework Equations p=mv p = sqrt of x^2 + y^2 The Attempt at a Solution...
50. ### Change of the angular velocity vector

Homework Statement I don't know how to solve part(b). See the photo Q3 for the question. Homework Equations The Attempt at a Solution See the photo 2010Q3 I found the torque and hence the new angular momentum vector. But I wonder how could this help me to find the angle...