All Questions
55
questions
-4
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1
answer
97
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Does every object have an infinite amount of energy? [duplicate]
If energy is defined as the capacity to do work, and the formula for work is force times displacement, if we place an object on a frictionless surface and apply any amount of force to said object, the ...
0
votes
2
answers
74
views
Why is the work done by moving an object up vertically not greater than mgh
Watching Walter Lewin's classical mechanics. In lecture 11 he says when moving object up vertically distance h, the work done by gravity is -mgh, which makes sense. But then he said the work done by ...
-1
votes
1
answer
63
views
Conservative forces and Variation
I am currently studying "Classical mechanics by Goldstein" and have just started. The book introduced something simple. For a conservative force, the work done in taking a mass from one ...
- 585
0
votes
1
answer
40
views
Getting different answers by different methods for angle made by a pendulum moving with constant acceleration
A point mass $m$ is hanging by a string of length $l$ in a car moving with a constant acceleration $a$. Using car frame and pseudo force, we easily get that the angle made by string with vertical is :
...
- 341
1
vote
1
answer
56
views
Conditions for a force to be conservative - Does the second condition imply the first? [duplicate]
John Taylor's Classical Mechanics says this...
I was wondering if the second condition already implies the first? I mean, are there situations where the first condition is violated even though the ...
- 97
1
vote
2
answers
98
views
Why is force "accumulated" more at a higher speed?
I tried to understand why kinetic energy is proportional to the square of velocity. In this endeavor I stumbled upon a book "Emilie du Chatelet: Daring Genius of the Enlightenment" (ISBN 978-...
- 112
1
vote
2
answers
108
views
Law of Conservation of Energy ambiguity in Giancoli textbook
In my version of the textbook by Giancoli: Physics for Scientists and Engineers, in chapter 8, there is a formulation of the law of conservation of energy that seems unintuitive and correctable to me. ...
0
votes
1
answer
46
views
Why is the force being the differential of a potential equivalent to it being a conservative force?
I was reading Goldstein's book on mechanics and came across this theorem:
$F(r) = - \nabla V(r)$ is a necessary and sufficient condition of the force field being conservative.
So far, I have ...
- 169
1
vote
1
answer
98
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Can Lagrange's equation be used if the virtual work done by constraint forces is not zero?
I'm learning analytical mechanics and was just introduced to d’Alembert’s principle, which I know is only valid when constraint forces' virtual work is zero. My question is, does this restriction also ...
- 468
1
vote
1
answer
90
views
Work done in sliding a block across a table, as seen in different inertial frames
Suppose, I'm pushing a block across a smooth table.
The length of the table is $d$, and the force that I applied is $F$.
According to an observer at rest, standing next to the table, the work done is $...
- 493
0
votes
2
answers
75
views
Is the value of the work done by the forces acting on a rigid body frame dependent?
I was going through the definition of "Work of Forces Acting on a Rigid Body" in Wikipedia .
Here they have mentioned that work done can be calculated by taking any reference point on the ...
- 1,568
0
votes
1
answer
258
views
Is impulse functionally equivalent to work and therefore expressible in Joules?
I am trying to understand things at at a fundamental and conceptual level.
Givens...
1 kg mass
Mass is at rest (relatively, of course)
Mass is on an idealized frictionless surface
1 N of force is ...
- 161
0
votes
3
answers
96
views
Why the weight vector is perpendicular to the displacement of the object being moved by the tension force in the conical pendulum?
Can someone explain why, in the conical pendulum, the weight vector is perpendicular to the displacement of the object being moved by the tension force in the system? I understand that the tension ...
user282164
20
votes
3
answers
4k
views
Conditions for a force to be conservative
Taylor's classical mechanics ,chapter 4, states:
A force is conservative,if and only if it satisfies two conditions:
$\vec{F}$ is a function of only the position. i.e $\vec{F}=\vec{F}(\vec{r})$.
The ...
- 1,295
0
votes
1
answer
138
views
Simple Force/Work Problem
In "Thinking Physics" there is a question about pushing a barrel up a ramp. The barrel is 100 pounds and the ramp is 3 feet high and 6 feet on the hypotenuse. The question is how much force ...
- 749
0
votes
2
answers
153
views
Does work increases as accelaration increases?
If work is a product of force and displacement, and force increases as acceleration increases, does these mean that work is dependent on acceleration? For instance, if I lift a block faster, does this ...
5
votes
4
answers
2k
views
Work done by constraint forces -- Generalisation
Consider the above scenario: In the subsequent motion, we need to find the work done by tension on the (trolley + mass) system.
Solution: Suppose at an instant, the velocity of the trolley (and hence ...
- 1,295
0
votes
1
answer
133
views
The "coefficients" of virtual displacement in Goldstein's classical mechanics
In Goldstein's classical mechanics the following passage is confusing me:
We therefore have as the condition for equilibrium of a system that the virtual work of the applied forces vanishes: $$\sum_i ...
- 6,963
0
votes
2
answers
459
views
Path independence of a conservative force
My book Halliday et al. gives a proof of the path independence (conservative force). It is said that the net work to move a particle from a to b and then from b to a is zero. Thus the work done from a ...
user248666
2
votes
3
answers
720
views
Work done by tension on a system-generalisation
In All the Classical Mechanics problems I have come across so far, There's one thing that happens invariably: That the work done by tension is zero. Mostly, It simply happens because the (massless) ...
- 1,295
0
votes
2
answers
615
views
Work done by friction over closed path
I am stuck thinking about work done by non-conservative forces. It is path dependent.
Let us consider an example.
A truck starts from rest and a block is kept on it. It accelerates for some time and ...
- 125
2
votes
1
answer
143
views
Example of a single constraint force doing virtual work despite the sum of work done by constraints being zero
When deriving d'Alembert's Principle it must be assumed, that the total virtual work done by constraint forces vanishes.
$$\sum_{j=1}^N\mathbf{C}_j\cdot\delta \mathbf{r}_j=0.$$
In the books I've read, ...
- 72
1
vote
2
answers
144
views
Work done as change of potential, how total derivative is converted to partial derivative
I am reading Goldsetein's Classic Mechanics 3rd edition in Chapter 1 it says,
If work done in moving form point 1 to 2 denoted by $W_{12}$, is independent of the path it should be possible to ...
- 113
0
votes
2
answers
192
views
In order for a force to be derived from the gradient of a potential energy, does the work done by such a force need to be invariant of the path?
Suppose a force $\mathbf{F} = \mathbf{F}(\mathbf{r}, t)$ where $\mathbf{r}$ is a three dimensional space vector and $t$ is time.
I understand that in order to a force be conservative two conditions ...
- 376
0
votes
1
answer
104
views
Equation for total work for a system of particles, modeled as a single particle, acted upon by multiple variable forces in three dimensions?
I am attempting to generalize the equation for the total work done by multiple, constant forces on a system that can be modeled as a single particle (that is, a system that moves so that all the parts ...
- 125
3
votes
4
answers
2k
views
Why the total virtual work done by forces from constraints vanishes? (Perpendicularity of two or more particles)
My mechanics book claims that the total force on the $i$-th particle is
$$
F_i=K_i+Z_i \tag{2.5}
$$where $Z_i$ is the force due to constraints and $K_i$ the real, dynamic force. Then, the book states ...
- 1,335
2
votes
1
answer
2k
views
Is total mechanical energy always equal to maximum potential energy?
Am I correct in stating this: When initial velocity of an object is $0$ then the total mechanical energy will always be equal to the maximum potential energy (with maximum height or displacement) (...
- 23
1
vote
2
answers
10k
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Work done by a person climbing stairs, who or what does the work? [duplicate]
I've seen other questions like this but didn't really see any answers.
When a person climbs stairs, the object is the person. Yet we say the person did work...how so? Doesn't work mean an external ...
- 379
3
votes
1
answer
358
views
Conservative field vs conservative force
For a conservative field (e.g. electrostatic field) the circulation of the field (along a closed line) is zero.
For a conservative force (e.g. macroscopic elastic force) the work performed on a ...
- 719
0
votes
1
answer
125
views
Force Applied but No Distance Travelled
Suppose I push on a wall with a constant force of 5 N for 10 s. The wall won't move and hence no work will be done on the wall. However, pushing requires energy. How can I find out how much energy I ...
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