6
$P$ is the instantaneous power; it only depends on the values of the force and velocity at a given moment $t$. It does not depend on the history of the force (i.e. if the force is constant, or varies with position or velocity).
It may seem confusing because you have written that the work $W = F \cdot x$. This is not true in general. Instead, the work done ...
4
Simply put: a conservative system conserves energy, a nonconservative one doesn't.
In a conservative system:
trajectories follow paths of constant energy - i.e., if you start the system with a given configuration and let it evolve according to its dynamics, the configuration (say, a particle's position and momentum) might change with time, but its energy ...
4
So you need to do work to change the external pressure at every point
as well which would be equal to the work done by the gas in expansion.
It is in this statement where you are going wrong.
Consider the following thought experiment. (See diagrams below). Let's say you have the gas in a vertically oriented frictionless cylinder and piston. On top of ...
4
I think it’s because given that the sheet is infinitely charged, the expression for the potential at r is not an approximation and it can be deduced using gauss law. The sheet creates an uniform electric field at any distance, therefore the work would be infinite.
3
Put a crate on a flatbed truck and have the truck drive in a circle while speeding up. The static frictional force that the flatbed exerts on the crate both keeps the crate moving in a circle and acts to speed the crate up along the direction of motion. By the time the truck has completed one full circle (and so hence so has the crate), the crate has sped ...
3
Strictly speaking, in physics an isolated system is a system which has no contact with the external world, including the possibility of exchanging work.
However, as in many other examples, sometimes the technical meaning in physics is not the same as in everyday language and the two semantic basins may cause some ambiguity. In some cases, we use the term ...
3
Suppose that the blocks are being pushed at constant speed each time (even though the speed is greater when the second man pushes. This presupposes that the block is already moving at the right speed at the start of the 2 m. Since the speed is constant, the mens' pulls must be equal to the frictional drag. Assuming that the frictional drag is independent of ...
2
For a quasi-static adiabatic process, less adiabatic work is done on the surroundings with internal friction (irreversible quasi-static process) than without internal friction (reversible quasi-static process). That is because part of the total work done by the gas is internal friction work and winds up as internal energy. Thus at any given volume during ...
2
I am a bit troubled trying to make connection between energy and work.
Work is one of two means by which energy can be transferred from one object to another by means of a net force acting on an object through a distance. The other means of energy transfer is heat, which is energy transfer due solely to a temperature difference between objects.
What I do ...
2
Thus work is frame dependent.
Is my conclusion correct?
Yes. Work is frame dependent. This can be easily seen by noting that distance is frame dependent and since $W=F\cdot d$ then work is also frame variant.
Note that the plank frame that you describe is non inertial. So energy is not trivial and is actually not even conserved in that frame. However, ...
2
The train is moving at constant velocity. The energy the person gains comes from internal energy, like chemical potential energy. So why does it look as if friction from the train to the person is doing work. I'm confused, what am I seeing. This makes no sense to me.
Let's imagine a person at rest with respect to the surface they're standing on, and they ...
2
But let's say I walk forward/accelerate on a moving train, train at a constant speed. And there is an observer sitting watching this outside. They would see friction doing positive work on me relative to the ground?
This is correct. The power, $P$, of a contact force, $\vec F$, is given by $P = \vec F \cdot \vec v$ where $\vec v$ is the velocity of the ...
2
Force causes things to accelerate according to Newton's second law $a = F/m$. By implication, you could say it causes movement, but this is a consequence of the acceleration and also the time it has been accelerating. Since the object is now moving the force has to be applied over a distance (and a period of time) to keep the object accelerating.
This is ...
2
One simple way is as follows: given $\mathbf{x}\equiv \mathbf{x}(t)$ we can write
$$\int_{\mathbf{x}_1}^{\mathbf{x}_2}\mathbf{F}(\mathbf{x}(t))\cdot d\mathbf{x} = \int_{\mathbf{x}_1}^{\mathbf{x}_2} \left(F_1(\mathbf{x}(t))dx + F_2(\mathbf{x}(t))dy+F_3(\mathbf{x}(t))dz\right) = \\
= \int_{\mathbf{x}_1}^{\mathbf{x}_2} (F_1(\mathbf{x}(t))\dot{x}+F_2(\mathbf{x}...
2
(a) By 'spring equilibrium' (your second paragraph) I think you mean unstretched (or natural) length of spring.
(b) "the mass pulls the spring down until it just about touches the floor." You need to consider this more carefully. You are also saying that the $mg =ky$ when the mass is just above floor level. This value of y is therefore the equilibrium ...
1
I get that work is essentially a measure of whether a force is
“successful” or not in displacing an object in its direction.
"Successful" has no meaning in connection with the definition of work. In its most basic form, work is one of the two basic means of energy transfer between objects, and is the result of the dot product of force times displacement. ...
1
Force is something that basically makes things accelerate (or can we
say move?); correct me if I'm wrong.
A force may be thought of as any influence which tends to change the motion of an object. Note that I have emphasized the term "tends", because a force does not necessarily result in the acceleration of an object. Only a net force causes acceleration. ...
1
Power is defined as rate of change of work. Since we are talking about derivatives, the power concerned is instantaneous power which is defined as
$$P = dW/dt$$
Now remember that by definition, work done
$$W = \int _C \overrightarrow F \cdot d \overrightarrow r$$
where $\int _C$ represents a line integral over the required path.
Therefore
$$dW = \...
1
Isolated System is a system through which neither mass nor energy can
pass. According to this definition, could it be implied that although
we could have no energy exchange, we can exchange Internal Energy for
work, as in a adiabatic process.
An adiabatic process is one in which a system does not exchange heat with its surroundings, but in which there ...
1
An electron in electric field has tendency to move opposite to the electric field. If it does so the work done by the field force is positive as the force on electron and direction of its movement is in same direction. More simply If the electron is in electric field the field pushes it towards the positive plate
From what i know, when a charge moves in ...
1
"What I do not understand is that this block has energy which means it has ability to do work but how does it do that?" Lasso the block with a rope and hang on to the rope. The block will come to rest exerting a force on you, the holder of the rope, through a distance as your hand is pulled forward. Work is done on your hand.
There are, of course many ...
1
The formula for the work done by a gas is 𝑊=∫𝑓𝑖𝑃𝑑𝑉. What
pressure should be used here?
It is always the external pressure.
I'm asking because I thought you use the gas pressure at every instant
of an expansion.
You do if the process is carried out reversibly (extremely slowly), that is, quasi-statically, so that the gas is always in ...
1
1) Work is done by the friction forces until the box stops.
2) Box kinetic energy is transformed to increased temperature (internal energy) of the sliding surfaces.
3) The cooling to the neighbourhood is an irreversible process, increasing entropy.
1
This is an answer to the original title:
Is friction work or heat?
Neither work nor heat. Friction is a force:
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other.2 There are several types of friction
In physics one has to be accurate in the use of terms, the units are ...
1
The gas is providing pressure (and thus force). On a microscopic level you have lots of molecules moving in random directions. If there was no piston the gas would expand. Without a wall to supply a force the particles keep on moving. When there is a piston the particles bounce off the wall. Newton's third law applies for every little particle that bounces.
...
Only top voted, non community-wiki answers of a minimum length are eligible
