# Tagged Questions

Geometric object with magnitude (length) and direction.

133 views

### What is the Vector/Cross Product?

I have decided to start learning physics before I am required to take the class in 11th grade so that I will be ahead of my classmates. I found a cheap physics book on amazon and ordered it but ...
83 views

### What's the physical meaning of change in momentum vector?

If I there is a initial momentum of 10Ns upwards, and final momentum of 10Ns to the right, I can find the difference in momentum by drawing a triangle and finding the resultant vector. But, how is ...
270 views

### Deriving cross product from angular momentum algebra

Is it possible to derive: $$\hat{L}=\hat{r}\times \hat{p}$$ from the angular momentum algebra: [\hat{L}_i,\hat{L}_j]=i\ \hbar\ \epsilon_{ijk}\hat{L}_k\ ? ...
86 views

### Why is parallel component of velocity along position vector considered rate of change of position?

If you have a position vector and a velocity vector of a particle, then the component of velocity vector along position vector is the rate of change of distance of the particle from the reference ...
71 views

### what does magnetic field vector mean?

I am trying to understand what a magnetic field vector tells us about the magnetic field. I understood that a vector is just a representation of a point and how much it is moved in x,y and z direction ...
126 views

### Making sense out of covariance and contravariance

I just read about co- and contravariant vectors and I am not sure that I got it right: If we imagine that we have a n-dimensional manifold $M$ then a tangent space is spanned by the vectors ...
48 views

### Is the flux through A the same as the flux through B?

In the figure below, the amount of field lines through A is the same as the amount of field lines through B, but can you say the flux through A is the same as the flux through B as well?
25 views

### Calculating uniform angles between 2 vectors [closed]

If I have two vectors, say: [100] and [101] and I want to calculate two angles between them, uniformly distributed, would it just be: [1 0 0.33] and [1 0 0.66]? So, [100] = 0 degrees [101] = 45 ...
33 views

### How do I show $e_r$ and its first- and second time derivative?

What does a charge q moving in a circular orbit with a constant velocity (a "rotating charge") and a stationary observer that measures the E field look like? And how do I show $e_r$ and its first- and ...
222 views

### Derivation of Jefimenko's Equation in Jackson's EMT book

I have been trying to understand the derivation of Jefimenko's equation in Jackson on p.246-247 which can be seen in the photographs attached. First of all I did not fully comprehend the ...
79 views

### Why taking components of a component of a vector is invalid?

Suppose there's a force $F$ of magnitude 10 newtons in the direction of positive y-axis acting on a particle A. I know that the particle would not experience any force in the positive x-direction ...
203 views

### Finding the magnitude of Two Vectors [closed]

Vector C has a magnitude 23.4 m and is in the direction of the negative y-axis. Vectors A and B are at angles α = 44.4° and β = 27.7° up from the x-axis respectively. If the vector sum A+B+C = 0, what ...
609 views

### Direction of electric field lines and electrostatic force

Direction of electric field and electrostatic force should be same by the equation $$\vec{F} = \frac{k q q_0}{r^2}$$ Electric Field $$\vec{E} = \frac{k q}{r^2}$$ Let us suppose that there is a ...
66 views

### When does $\mathbf n\times(\nabla V_2-\nabla V_1)=0$ imply $V_1=V_2$

I was reading a paper on electrohydrodynamics which has the following sentence (in my own words): At the interface/boundary, the requirement of continuity of the tangential component of the ...
22 views

146 views

### Tension on a string

A string is attached at both extremities and put under tension $T_0$ at rest. We know that if we pull the string upwards from the middle, the tension will increase. But why is it that, admittedly, ...
894 views

### Difference between Speed and Velocity

What is the difference between Speed, Velocity and Acceleration? Could any one describe it pictorially?. I am more over confused even after investigating many times. I am unable to relate myself ...
905 views

### Is a vector and a unit vector dimensionless

Lets say I have a position vector $\vec r$. Is it dimensionless or does it have a dimension of length i.e $[L]$. Also does the unit vector $\hat r$ have a dimension?
161 views

### Is the Mass flow rate (Mass flux) a scalar quantity?

Wikipedia states that mass flow rate is a scalar quantity, however Mass Flow Rate= Density x Cross Sectional Area x Velocity and velocity is a vector quantity, so this would imply Mass Flow Rate is ...
152 views

### A particle is constrained to move around the unit circle in the xy plane according to (x,y,z) = (cos(t^2),sin(t^2),0) t >= 0 [closed]

A particle is constrained to move around the unit circle in the xy plane according to (x,y,z) = (cos(t^2),sin(t^2),0) t >= 0 At what point should the particle be released to hit a target of (2,0,0)? ...
269 views

45 views

### How can a vector have both contra-variant and co-variant components? [duplicate]

I have read that contra-variant and co-variat vectors have different transformation properties , which distinguish them, yet at the same time I have read that a vector can have contra-variant and ...