Friction & Work: Questions & Answers

[timetoplearn]

two equally important questions:

If work=forcexdistance, how does a galvanic cell do "work" if there is not force nor any distance traveled by the force.

question 2: Friction is a NC force that increases internal energy. Right?
Doesn't friction also cause heat?

My physics book says:

If no heat: mechanical energy= KE+PE+Internal Energy

If no heat and no frictionME=PE+KE.

How can you have friction without heat?

Also can you tell me a brief description between q, deltaH, and U


by the way if you saw this on another forum, it is because I asked it on another forum, but got a semi-incomplete answer.

this is the answer I got for your reference:
Imagine what happens to space shuttle when it's going back to Earth from orbit: molecules of spaceship are colliding with air molecules (denser and denser with lower altitude).
High velocity of vehicle + pretty normal velocity of air molecules (~343 m/s) results in heating spaceship to 1650 C..
http://en.wikipedia.org/wiki/Space_Shuttle...otection_system
This is pretty extreme example.

Any air molecules colliding with anybody that has some velocity is resulting in taking part/all of kinetic energy from that body (or particle), which is resulting as acceleration of air molecules, and deceleration of body. Until both bodies have the same temperature.

And the same happens when we slide some body, on another body like table.

The only difference is scale.

 

[UltrafastPED]

Both of your questions require that you look at the microscopic situation.

For friction the work done always opposes the motion, and results in heat at the interface between materials; some goes into the book, some goes into the table.

For a galvanic cell you can look at the traveling ions in the solution. It will reproduce the Joule heating law for a resistive circuit, and will heat the solution which carries the ions.

 

[timetoplearn]

Why is there two different formulas for ME one with friction but no heat and one with no heat?

 

[UltrafastPED]

Internal energy could be elastic energy or sound, etc. Heat is a disorganized (random) motion which is usually treated as distinct from other "internal energy".

The reason is that thermal motion is non-reversible (leading to the second law of thermodynamics), whereas most other forms of internal energy are reversible.

Heat still follows the laws of mechanics, but it is usually studied as a separate topic.

 

[PJC01]

I would like to first clarify that the concept of work in physics is different from the everyday use of the term. In physics, work is defined as the transfer of energy from one system to another. This can be done through various means, including applying a force over a distance, as in the equation work = force x distance. However, this is not the only way work can be done. In the case of a galvanic cell, work is done by the transfer of electrons from one electrode to another, resulting in the production of electrical energy. This energy can then be used to power devices or do other forms of work.

To address the second question, it is correct that friction is a non-conservative force that increases internal energy. This increase in internal energy can manifest as heat, as the kinetic energy of the moving bodies is converted into thermal energy due to the frictional forces. However, it is important to note that friction is not the only source of heat. Other forms of energy, such as electrical or chemical energy, can also be converted into heat.

Regarding the concept of q, deltaH, and U, these are all related to the transfer of energy in a system. Q represents heat, or the transfer of thermal energy, while deltaH represents the change in enthalpy, which is the total energy of a system. U represents internal energy, which includes all forms of energy within a system, including thermal, kinetic, and potential energy. These concepts are all important in understanding the energy changes that occur in a system, especially in thermodynamics.

In summary, work can be done through various means, not just by applying a force over a distance. Friction is one way that energy can be transferred, resulting in an increase in internal energy and often heat. The concepts of q, deltaH, and U are all related to the transfer of energy in a system and are important in understanding energy changes.