All Questions
39
questions
2
votes
1
answer
114
views
Why can we calculate force on a dipole from torque?
In the Feynman lectures he derives the (mechanical) energy of a dipole
$$ U = -\boldsymbol{\mu}\cdot \boldsymbol{B} + \mathrm{constant}$$
by considering only the torque on it in a uniform field. He ...
- 2,122
0
votes
0
answers
58
views
How can Torque and Work have the same dimensions (both can be expressed in N.m because Joules = m.N = N.m) but they represent diffrent quantitie?
So torque and work are both distance times force but how can they be so different conceptually? I understand the torque is an outer product and is a vector while work is a dot product and is a scalar ...
1
vote
2
answers
210
views
Is Joule equivalent to Joule/radian? [duplicate]
The work a constant torque does when it moves a particle through an angel $\theta$ is given by $\tau \theta$. The work is measured in Joule, so the torque should be measured Joule/radian, but the ...
- 959
3
votes
1
answer
204
views
What does the geometric product between displacement (or maybe position) and force vectors mean?
So work is measured in joules, which is newton * meter, and it is calculated by taking a scalar product between displacement and force vectors.
And torque is very similar, it is newton * meter too, ...
2
votes
2
answers
254
views
How does a magnetic field do work on rotating a current loop?
Lorentz force tells us that the force on a charged particle by a magnetic field is always perpendicular to its velocity. So its a pretty well known fact that a magnetic field doesn't do work.
But we ...
- 21
0
votes
1
answer
76
views
Help me understand power and torque [closed]
I'm trying to understand power and torque relationship in terms of cars.
Let's assume we have a four tracks with a load that needs a total of 1000N to move.
First one has 1000 Nm and 1000W
Second ...
- 1
0
votes
1
answer
311
views
Derivation of work done by external torque
In this derivation, why isn't external torque the negative of torque of electric field and therefore Text = -PE sinø
- 69
1
vote
2
answers
403
views
Work Done on a rotating thin rod by hinge Forces
So I was studying the concept of rotational energy through a video, and the guy presented a problem,
It's like this:
"Suppose a thin rod of mass M and length L/2 is hinged from one end. Then, it ...
- 444
1
vote
2
answers
57
views
This question is about motor power requirements
If I have a motor that has a power of 20 kilowatts, does that mean that the motor can produce a torque of 10k newtonmeters at 2 rpm, or analogously a torque of 2 newtonmeters at 10k rpm since the ...
- 11
3
votes
4
answers
917
views
Why don't simple machines change the amount of energy needed?
Suppose I wanted to tighten a nut and I do so using two spanners of different arm lengths, say of $10 \text{ cm}$ and $20 \text{ cm}$. According to a an online source:
A spanner counts as a simple ...
- 413
0
votes
1
answer
164
views
What's the meaning of unit of moment $\mathrm{N\cdot m}$? How do you explain it? [duplicate]
I know the meaning of units with division like $\mathrm{m/s}$ or $\mathrm{m/s^2}$ etc. they make sense, like $2\ \mathrm{m/s}$ is like the car pass $2\ \mathrm m$ in $1$ second, you know what I mean?
...
- 101
0
votes
3
answers
480
views
Is $d\theta$ a vector and does the equation $d\vec{s}=d\theta \times \vec{r}$ make sense?
I was reading about torque on Wikipedia and I found this passage (in the section "Relationship between torque, power, and energy")
The work done by a variable force acting over a finite ...
- 311
10
votes
6
answers
7k
views
Why does a rolling sphere slow down if work done by friction on it is zero?
When we push a sphere on a rough horizontal surface, it slows down because there is a net torque on it (by normal force and friction acting in opposite directions) and this causes its angular speed to ...
- 353
1
vote
1
answer
37
views
While unwrapping a rope the torque due to tension shouldn't do work as the point of contact does not move while the torque is being applied?
This explains my question in more detail
If you don't get what I am asking feel free to comment I would try to improve my question
- 117
1
vote
1
answer
130
views
What is the distinction between work done by torque and force about an axis other than centre of mass?
Suppose a point particle is undergoing circular motion about a fixed point such that a tangential force is accelerating its speed continuously. Now I believe that I can calculate the work done on this ...
- 1,568