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
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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
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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 ...
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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
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
1
vote
1
answer
35
views
If a cylinder skids what can we say about the work of friction on it
A cylinder skids on a rough horizontal plane and we know that a frictional force will act on it.
What can we say about the work done by friction?
I believe that the frictional force is forward, the ...
- 1,270
0
votes
0
answers
36
views
Work and mechanical energy relationship for a rigid body
For a single particle in a conservative field, I know that the work done by an external non conservative force $W_n=\Delta M$ where $\Delta M$ is the total mechanical energy.
Is the same true for an ...
- 1,270
0
votes
2
answers
122
views
Is work done by the normal reaction force when an object is dropped on the ground?
When a perfectly non elastic object (let's say a book) is dropped on the ground, it's kinetic energy from the fall is transformed into heat and sound.
Now, if W = Fs, the work done by the normal ...
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-2
votes
2
answers
46
views
Equation for Work required to achieve a certain velocity [closed]
If we are trying to find the work required to get an object moving at velocity $v$, and we start with $w = f\cdot d$, we can then make the following substitutions:
substitute $f$ with ma: $w = m\cdot ...
1
vote
2
answers
50
views
Calculating work done vs. calculating final energy [closed]
I'm trying to solve for work after 2 seconds given $v(t)=3t^2$ and mass$=1kg$. There are 2 approaches:
Just calculate kinetic energy after 2 seconds: $E_k=.5*mv^2 = .5 *1 * (3*2^2)^2 = .5* 144 = 72J$
...
0
votes
3
answers
52
views
Does work between 2 bodies depend on their relative speed?
Imagine a car standing on the road. Now the car starts to accelerate.
On the first part, the car accelerates from 0 m/s to 10 m/s.
Some of the fuel was used during this first part. let's call that ...
- 105
0
votes
3
answers
334
views
Can you define Work as the amount of energy transformed within a system?
Sorry for the relatively long post! Thank you for reading and let me know if there is anything I can clarify/fix.
My textbooks defines Work in the following way:
A measure of the amount of energy ...
- 1,288
0
votes
1
answer
104
views
First principle of thermodynamics vs classical mechanics
please I need clarification about the first principle of thermodynamics, it's general statement is:
$$\Delta U + \Delta \text{KE} + \Delta \text{PE}= W + Q .$$
Supposing that: $ΔU = 0$ and $Q = 0$, ...
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
0
votes
1
answer
481
views
What came first: the work-energy theorem OR work and energy individually which were later reconciled in a theorem?
What came first: the work-energy theorem OR work and energy individually, which were later related to each other by a theorem?
Were work and kinetic energy defined after arriving at the work-energy ...
0
votes
4
answers
80
views
Work done involving two equal objects
I just want to check my understanding. Say I have two equal mass blocks A and B, being pushed together by force $F$ by a distance $D$; ignore friction.
Technically, the total work by $F$ is $FD$, but ...
- 379
8
votes
11
answers
1k
views
Is it more work to put more (apparent) effort to get the same outcome?
I was taking my dogs for a walk yesterday evening when this question occurred to me.
The two dogs were pretty enthusiastic about the walk and wanted to run on ahead, so the leads were taut and they ...
- 257
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 ...
- 251
0
votes
2
answers
98
views
How is energy conserved in terms of "Work"
Basic equation of work is given by $F\cdot s$. When work is done, the energy is stored either in form of potential or kinetic. My question arises when we look at a case of applying $m g$ of force ...
- 434
0
votes
0
answers
47
views
Work a medium of energy conversion? [duplicate]
Is work a medium to convert one form of energy to other? i.e. to say without work you can't convert type of energy?
Similar type of question pertains to heat.heat is also medium of conversion of ...
- 11
0
votes
2
answers
126
views
How to derive $dW = dE$? [closed]
From the definition of power:
$$P \ = \ \frac{dW}{dt} \ = \ \frac{dE}{dt}$$
Multiplying both sides by $dt$, we get:
$$dW = dE$$
$1.$ What does this imply?
$2.$ Are there any other (perhaps more ...
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4
votes
7
answers
634
views
Why does incline on treadmill burn calories faster?
So I was at the gym today, running on the treadmill, when the question hit me:
If I run with the treadmill on incline, I burn more calories. Since I run at the same speed, kinetic energy is constant, ...
- 163
1
vote
2
answers
439
views
Why is the work done by friction zero when body is rolling? [duplicate]
Why is the work done by friction zero when body is rolling? Does it mean no energy is dissipated by friction.
0
votes
1
answer
833
views
Formula for Power from Kinetic Energy
Work Done = $Fd$
Power = $Fv$
If the (net) Work Done = Change in Kinetic Energy, and the object starts from rest:
Work Done = $\frac{1}{2} mv^2$
Power = $\frac{1}{2} m av$
Power = $\frac{1}{2} ...
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