All Questions
70
questions
0
votes
1
answer
36
views
Drawbacks of Quasi-Static process for lifting a block
Definition of Quasi-static: A quasi-static process is a thermodynamic or mechanical process that occurs very slowly, allowing the system to remain in a state of equilibrium at all times.
While ...
- 21
0
votes
2
answers
48
views
Is it possible that work is being done on an object, it's kinetic energy doesn't changes and still the body is transferred from one point to another?
Recently, I read a book about Electrostatics which stated that "Electrostatic Potential at a point is defined as the work done to move a unit charge from a reference point (generally taken as ...
-4
votes
1
answer
97
views
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 ...
2
votes
2
answers
102
views
Where does $W = \Delta E$ come from?
My textbook states the following:
$$W_{net}=W_{non−conservative}+W_{conservative}$$
$$W_{non−conservative}=ΔKE+ΔPE$$
$$W_{conservative}=−ΔPE$$
$$W_{net}=ΔKE$$
$$W=FDcos(Θ)$$
However, my teacher states ...
- 23
0
votes
1
answer
86
views
Why isn't work $Fd \sec \theta$? [closed]
In the following image if force the triangle PAN was right angle at P then the component of force in the direction of displacement would be $F\sec\theta$ so work $F*Displacement(AC)*\sec \theta $.
I ...
-1
votes
1
answer
79
views
Is there a non-counterfactual definition of energy? [duplicate]
I have once heard that the definition of energy is "the ability to do work". However, that is a counterfactual definition, because a physical system can have that ability without actually ...
- 1,252
0
votes
6
answers
291
views
Does potential energy actually exist? Or is it just a useful mathematical model? [closed]
The title basically covers it. I've actually thought about this question for a while now, and I am still not sure if I have a definitive answer. Most potential energies seem to just be the work that ...
- 183
4
votes
2
answers
934
views
How do we justify that work is a "transfer of energy" in the general case?
By the work-energy theorem, we can justify that the work on a particle due to the net force equals the change in kinetic energy of the particle. In compact notation,
\begin{align}\tag{1}
W_{\text{net}}...
- 8,640
0
votes
1
answer
283
views
Why do manual treadmills burn more calories than automatic treadmills?
Studies show that manual treadmills burn 30% more calories than automatic ones.
Let's assume that there is no air friction.
The figure is a diagram of the forces acting on a person running on the ...
- 305
0
votes
3
answers
88
views
Consolidating two ways to calculate work
I was wondering if I could get some help closing some fundamental gaps in my intuition of work, as it relates to force and distance travelled.
Scenario
Say we pull a 1kg box along the ground. We pull ...
- 163
1
vote
1
answer
91
views
Kinetic and Potential Energy of a multi degree of freedom (MDOF) system
Consider the following MDOF system:
$M\ddot x+Kx=F$
where $M$ and $K$ are the mass and stiffness matrix respectively, and $x$ and $F$ are the displacement and force vectors.
How can one determine the ...
- 15
0
votes
5
answers
97
views
How can potential energy increase? [closed]
If work is done on a body, the energy of the body increases. If work is done by the body, energy decreases. When we take a body up to some height, some work is done by us on the body, which is stored ...
0
votes
1
answer
319
views
How can the Joule be the unit of both work and energy?
Say a person applies 1 N to a box with a mass of 1 kg, displacing 1 m. This is one Joule of work
(1 N for 1 m).
Now say the person applies 1 N to a box with double the mass, displacing 1 m as well. ...
- 19
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
156
views
What work does a microwave oven do? [duplicate]
I learned that when energy is transfered it either produces work or it becomes thermal energy (heat).
Work implies a force that acts on an object producing changes in its position.
I'm learning these ...
- 111
2
votes
0
answers
141
views
What is the status of the Work-Energy Theorem? [closed]
All the 'proofs' of the Work–Energy Theorem that I have seen show that the work done by the resultant force acting on a body is equal to $\Delta \left(\tfrac 12 m v^2)\right)$ for that body. [It's ...
- 36.1k
0
votes
3
answers
432
views
Goldstein: derivation of work-energy theorem
I am reading "Classical Mechanics-Third Edition; Herbert Goldstein, Charles P. Poole, John L. Safko" and in the first chapter I came across the work-energy theorem (paraphrased) as follows:
...
- 232
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
0
votes
1
answer
45
views
Is the definition of work related to the nature of the fundamental interactions?
I am having troubles trying to understand why is work defined as it is.
So, I know how work is defined: $W = \vec{F}\cdot{}\vec{d}$ (F is the force, d the displacement) and I am okay with it. This, ...
- 23
0
votes
0
answers
689
views
Lagrangian intuition [duplicate]
I am new to lagrangian mechanics and it just baffles me the idea of subtracting potential energy from kinetic energy. Why don't we use kinetic energy alone and the least action path (between two ...
- 105
0
votes
2
answers
96
views
Is net force conservative?
From the work-energy theorem, $$\int_{C}^{}\vec{F}\cdot d\vec{r}= \frac{1}{2}mv^2_f -\frac{1}{2}mv^2_i$$
Is velocity the gradient of position, and if so, does that make this force a conservative ...
- 65
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
434
views
Kinetic energy constant, but net Work done is not $0$
Suppose I have two objects of equal mass and volume, in space, in contact with one another.
The two objects exert equal and opposite gravitational force on each other. Let us apply a force $F$ on one ...
- 493
2
votes
2
answers
282
views
Work done on an object whilst lifting it
Imagine to lift an object with mass $m$ from height $h_1$ to height $h_2$ and neglect the friction with air. How much work have you done on the object?
My answers (big doubt in the second one!):
...
- 1,319
1
vote
1
answer
340
views
Can average power be non zero, but instantaneous power be zero
Q. A wind-powered generator converts wind energy into electric energy, Assume that the generator converts a fixed fraction of wind energy intercepted by its blades into electrical energy. For wind ...
- 125
0
votes
4
answers
163
views
Definition of Power
I wanted to clear my doubts regarding the true definition of power. Imagine a mass falling from a height and reaching the ground thanks to gravity. The power of this event would be the work done by ...
- 161
0
votes
1
answer
34
views
Does this vector need to be fixed for the kinetic energy to be constant?
I was solving the following homework problem:
A force $\vec{F} = \vec{k} \times \vec{v}$ is applied to a particle of mass $m$. Here $\vec{k}$ is a fixed vector and $\vec{v}$ is the velocity of the ...
- 207
1
vote
1
answer
40
views
Conceptual question about rotational and translational kinectic energy
My real life problem is to calculate initial translational and angular velocities of a vehicle in a loss of control to a stop (the vehicle will translate and rotate about it's center of mass.)
Initial ...
- 111
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
2
votes
2
answers
775
views
How does the work-energy theorem relate to the first law of thermodynamics?
The work energy theorem states that the net work on a particle is equal to the change in the kinetic energy of the particle:
$$W_{net}=\Delta K $$
My first question is whether this formula (the work-...
- 1,581