New answers tagged forces
0
votes
Relations between the strong form of Newton's 3rd law and conservation of angular momentum?
Newton's Third Law can be written as
$$ \vec{F}_{ab} = \vec{F}_{ba} $$
The strong form addendum can be written as
$$ (\vec{r}_a - \vec{r}_b) \times \vec{F}_{ab} = (\vec{r}_a - \vec{r}_b) \times \vec{F}...
- 43
5
votes
Relations between the strong form of Newton's 3rd law and conservation of angular momentum?
For a system of $N$ particles with the $i$th particle of mass $m_i$ at position $\mathbf r_i$ with velocity $\mathbf v_i$ , the total angular momentum about some point $\mathbf r_0$ (which we will put ...
- 58.6k
1
vote
Relations between the strong form of Newton's 3rd law and conservation of angular momentum?
The rotational equations you are referring to are designed to handle rigid bodies. If you add the rigid body equations to your system (the distance between any two points on an object does not change)...
- 51.7k
-1
votes
Influence of wind on an aircraft’s ground speed
I'll start by addressing the ChatGPT argument. ChatGPT is notoriously for making good looking arguments that lack content (or are even wrong). "Wind isn’t a force" is true, but only on a ...
- 51.7k
0
votes
Influence of wind on an aircraft’s ground speed
You are both right.
The airplane doesn't know the ground is there. It flies in circles at constant speed through the air. Anything that moves in a circle is accelerating toward the center of the ...
- 45.7k
0
votes
Can non-free forces change the rest mass?
Thus, we see that in special relativity the action of a force can alter the rest mass fo a particle!
This demonstration of force changing the rest mass is nonsense, based on a misconception of what ...
- 41.4k
2
votes
Accepted
Does $\vec F=I\int\mathrm d\vec{l}\times \vec{B}$ give the force on a current carrying wire when it is in motion?
You are correct; although the usual simple derivation works only for stationary conductor, the result is more general and holds for moving conductor as well.
One way to see it is the argument you gave ...
- 41.4k
0
votes
How to obtain nodal forces from stress tensor?
This text does not answer your question.
The following information may be familiar,
but is included because it is a simple and convenient method when the material property is linear.
How to obtain ...
- 990
0
votes
Why does that screw-propelled vehicle steers opposite to common sense?
I can only offer some comments, which may or may not be useful. According to the offscreen voice in Russian, initially the vehicle's control was poor, but it improved when they started to use a screw ...
- 27.5k
0
votes
Does $\vec F=I\int\mathrm d\vec{l}\times \vec{B}$ give the force on a current carrying wire when it is in motion?
Your conjecture is not true. Consider the following cases:
If the magnetic field is non uniform : the formula $F = I d\vec{l} \times \vec{B}$ will be applicable but due to the change in magnetic flux ...
0
votes
Finding the accelerations and tension of a pully wedge system
It seems tedious but not very complicated.
You don't show what is your answer or how you arrive to it. So if you are making a mistake for example in the the forces you put in the 2nd law equation, we ...
5
votes
Can you directly feel the effect of gravity, or only opposing forces?
You are almost completely right.
What we do not and cannot feel is a uniform gravitational force. By “uniform” here I mean in the sense of general relativity where the force of gravity is just a ...
- 109k
1
vote
Is the $\Sigma$ in Newton's second law the sum operator or an "arbitrary" notation?
This is not a physics question, it's a notation question. In most books, you'll find
$$\sum \vec{F} =m\vec{a}, $$
where $\sum$ is the summation symbol. The expression
$$\Sigma \vec{F}=m\vec{a} $$
...
- 3,603
0
votes
Is the $\Sigma$ in Newton's second law the sum operator or an "arbitrary" notation?
The sum operator $\sum$ is just the greek letter $\Sigma$ (= S in our alphabet) but bigger. It's not an accident. It's just the first S of the word "Sum". It's the same reason why we use a &...
- 41
1
vote
Is the $\Sigma$ in Newton's second law the sum operator or an "arbitrary" notation?
Newton’s law, correctly stated with a summation, is
$$\sum_{i=0}^{n-1}F_i=ma$$
for mass $m$, acceleration of the system $a$, and all $n$ forces considered $F_0,F_1,…,F_{n-1}$.
I don’t know why someone ...
- 3,479
1
vote
In special relativity, can a transfer of energy increase only the mass of a point particle and not its speed?
Mass is (internal) energy in the rest frame, hence for 'a point particle without internal degrees of freedom' there is no way to change its mass. The concept of mass is only useful if it is constant. ...
- 26.6k
0
votes
In special relativity, can a transfer of energy increase only the mass of a point particle and not its speed?
The invariant mass can't change due to a net force. By a net force here I mean, a force that does work on the system. In SR it is often called a "pure" force (see robphy's answer for more ...
- 3,313
4
votes
Accepted
In special relativity, can a transfer of energy increase only the mass of a point particle and not its speed?
Here is a possibly useful energy-momentum diagram (from my answer to How is the time-component of the spacetime interval in a spacetime diagram related to the time component of the energy-momentum 4 ...
- 12.4k
0
votes
In special relativity, can a transfer of energy increase only the mass of a point particle and not its speed?
The mass of a fundamental particle is a constant, any energy you add results in a change in momentum (and thus also kinetic energy), not in the mass.
Remember that
- 1,809
0
votes
In special relativity, can a transfer of energy increase only the mass of a point particle and not its speed?
Everything is specified in the inertial lab frame. Then, is this a well-posed problem with a single deterministic solution integrated from the equations of motion? Or do I still need to specify the ...
- 11.2k
0
votes
Balancing of forces after the deformed body comes to equilibrium
electrostatic forces would weaken upon increasing the intermolecular
distance
It looks like you are referring to Coulomb's law for the force between electrical charges. But the forces associated with ...
- 77.9k
0
votes
Balancing of forces after the deformed body comes to equilibrium
The resolution lies in the balance (modeled by an interatomic potential) of attractive and repulsive forces in solids. The average intermolecular distance is set by this balance.
If you deform the ...
- 28k
3
votes
Is there a principle that determines the tension in this system?
Apologies for posting a second answer. My first answer addressed what I considered to be the more realistic case of non-infinitely rigid connections. This answer specifically addresses the ...
- 10.1k
1
vote
Is there a principle that determines the tension in this system?
The way to approach friction problems is to consider all the sliding contacts as sticking first and finding the friction force required to enforce the sticking.
Assume all bodies have zero ...
- 3,345
1
vote
Is there a principle that determines the tension in this system?
The problem is poorly worded. "Pulled on a rough surface" could be interpreted to mean the blocks are in motion, in which case the coefficients would be for kinetic friction. But that would ...
- 77.9k
2
votes
Accepted
Is there a principle that determines the tension in this system?
For convenience I will label the blocks as $m_1, m_2, m_3$ from right to left to be consistent with the labeling of the tensions in you diagrams.
For simplicity consider a single block of mass $m$ ...
- 10.1k
-1
votes
Can a glass screen protector reduce the impact on a phone?
"Glass only breaks when the force of impact finally overcomes the surface compression. A scratch doesn’t shatter glass, but small stresses will eventually lead to it shattering."
With a drop ...
1
vote
Is there a principle that determines the tension in this system?
You are essentially asking about the distribution of static friction when an extended body at rest on a rough surface is pulled from one end. The answer is that it is indeterminate without more ...
- 12.9k
0
votes
How to determine if there is frictional force?
Ignoring creep, the left board does not provide friction if it suddenly becomes rough. (If you find the sudden emergence of mechanical friction far-fetched, replace it with an adhesive bond that sets.)...
- 28k
2
votes
How to determine if there is frictional force?
When you way "coefficient of friction," that leads me to assume you are talking about Columb friction, where we model friction as a force that opposes motion which can be up to some constant ...
- 51.7k
1
vote
Limits of the integral for the calculation of work
This response is specifically to this section of your question:
I know that for potential energy the above statement is correct, one can choose the reference (zero) value as one wishes. But, for ...
- 22.6k
2
votes
How to derive the formula of the buoyant force?
First, let's derive the basic buoyancy equation.
The rectangle on the left represents a vertical cylinder of water of height $H$. The pressure ($P_H$) exerted at depth $H$ is equal to the weight of ...
- 10.1k
3
votes
Limits of the integral for the calculation of work
I think this is one of the cases when we apply a rule beyond its applicable limits.You cannot define boundary conditions to quantities which describe energy transfer because they dont physicaly make ...
- 372
5
votes
Limits of the integral for the calculation of work
One way to think of an expression like $dW = F dx$ is that it is a physicist shorthand for a differential equation. In this case, the differential equation for $W$ is a first-order ODE
$$
\frac{dW}{dx}...
- 55.4k
0
votes
Limits of the integral for the calculation of work
When you integrate a function, the limits of integration always have the units of the differential. We usually integrate from a starting unit to a generic unit. In that case, you would integrate:
$$
\...
- 1
4
votes
Will there be any frictional force from surface when an external force acts upon a body which is in contact with wall?
Let's assign a value of $0.5$ for the coefficient of static friction and $0.2$ for the coefficient of dynamic friction. This means the limiting static friction would be $2.5$ Newtons and the dynamic ...
- 10.1k
1
vote
Friction and normal reaction from a wall
But if you keep pushing with the same force, will there be any
friction at all (and only normal reaction from wall) or any normal
reaction from wall (and no friction) or both?
As long as the applied ...
- 77.9k
-1
votes
On the infinite range of the electromagnetic force
The infinite range of electromagnetism is an experimental fact that is accurately described by Maxwell’s equations.
- 26.6k
1
vote
Friction and normal reaction from a wall
To add to Dale's answer, one of the interesting challenges that arise when teaching introductory physics is that you typically simplify the physics so much that you can create really strange ...
- 51.7k
1
vote
Friction and normal reaction from a wall
As with my answer to the previous question, this system is statically indeterminate. That means that only applying Newton’s laws leads to a system of equations with multiple solutions.
To solve a ...
- 109k
3
votes
Accepted
Will there be any frictional force from surface when an external force acts upon a body which is in contact with wall?
All of those scenarios are possible. The system is statically indeterminate.
To determine which of these cases is correct requires additional information. Specifically, we need to know the stress in ...
- 109k
0
votes
Question about signs of forces
There is a misprint in the textbook.
$\dfrac{F_2}{F_{\rm T}}={\LARGE\color{red}-} \left(\dfrac{\partial y}{\partial x} \right)_{x_2}$ should read $\dfrac{F_2}{F_{\rm T}}={\color{red}{\LARGE +}} \left(...
- 99.9k
0
votes
Question about signs of forces
I do not understand why $F_T$ is not considered positive in one direction and negative in the other.
The author has implicitly assigned a tension $F_T$ to one end of the string segment and then used ...
- 28k
1
vote
Work done by static friction on a car
This answer is correct, but I'd like to emphasize an important point:
Work and total energy depend on the reference frame.
In the frame where the road is at rest, the car is gaining kinetic energy, ...
- 3,833
1
vote
Can the slack in 2 different strings (ideal) be transferred to one another?
If you cut the string you obtain the string tension $~T~$
I) write the equations of motion
$$ m\,\ddot X=-m\,g+2\,T\\
m\,\ddot Y=-m\,g-2\,T+T\\
m\,\ddot Z=-m\,g+2\,T$$
II) obtain the tension ...
- 12.9k
0
votes
Rolling Friction Value
Frictionless would mean that energy was not lost, it did not transfer away.
Energy is transferred by force over distance. If the two bodies could be so rigid that
the protrusions on the lower surface ...
- 43
0
votes
Is there a curve such that a ball rolling down it has constant velocity?
.
A freebody diagram of the ball will have three forces, ideally in a vacuum. Weight, normal and friction forces. The difference in direction of the normal force and weight add to a resultant force. ...
- 51
0
votes
Is there a curve such that a ball rolling down it has constant velocity?
If gravitational potential energy is not allowed to be dissipated and energy conservation must be obeyed,- then answer is NO, such constant speed curve does not exist. But, if potential energy ...
- 14.9k
1
vote
Is there a curve such that a ball rolling down it has constant velocity?
Without friction, the curve is a horizontal line.
- 1,894
6
votes
Is there a curve such that a ball rolling down it has constant velocity?
Lorenz'z answer is the correct one if the only force operating on the ball is gravity. If you add friction then there will instead be a 'curve' consisting a path of constant slope.
The only way to get ...
- 3,321
Top 50 recent answers are included