A dumb question

[steve_bank]

Identify all external and internal forces and sketch a diagram to show the resultant force vector. Does it oppose rotation?

I ca;'t do it off the top of my head on the scale of the Earth a, geology, and astrophysics, but that is how I would approach it.

The vector sum of all applied forces must equal the resulant force.

 

[bilby]

I take the descent into abject punnery as strong evidence that the question has been adequately answered.

While that is likely the case in this instance, I would warn you that I rarely need any such excuse.

 

[Elixir]

Yes the effect may be immeasurable by our instruments, but unless you abandon LOT and conservation there is an effect.

It does say “ directly effect”. I think the imprecision is in considering the pendulum/earth a closed system, which of course it’s not. There is still an effect but no reason that it has to accrue to or against the earth’s angular momentum: it can all be expressed as heat, right?

(IANAP)

 

[steve_bank]

Looking at it from conservation.

Motion of the Earth supplies energy to the pendulum. Earth's kinetic energy is converted to the pendulum kinetic energy and some is lost in friction showing up as heat. Entropy says all of the energy transferred to the system cannot be used to do useful work in the system. Some is lost. The heat however small is transferred to the mass of the Earth, and heat is radiated into space.

In the end kinetic energy is lost from the Earth. Within a finite volume or boundary perpetual motion or a lossless system can not not exist.

It is not theoretical for me, when I was befuddled by a problem that is one way I approached it. LOT.

A continuity equation defines where all the mass and energy goes. The assumption is causality and conservation of mass and energy are true. It is a very powerful analysis tool because it applies to all systems regardless of the processes.

Continuity equation - Wikipedia

en.wikipedia.org

A continuity equation or transport equation is an equation that describes the transport of some quantity. It is particularly simple and powerful when applied to a conserved quantity, but it can be generalized to apply to any extensive quantity. Since mass, energy, momentum, electric charge and other natural quantities are conserved under their respective appropriate conditions, a variety of physical phenomena may be described using continuity equations.

 

[steve_bank]

A PDF thermodynamics text if anyone is interested.

https://soaneemrana.com/onewebmedia/Thermodynamics%20by%20PK%20Nag.pdf

 

[Loren Pechtel]

It will very slowly lose it's spin.

1) Tides. Sure, it's tiny. It is not zero. A tiny force over a sufficient period eventually adds up.

2) Jeans escape. The atmosphere will be slowly lost to space. The molecule that escapes will carry away a disproportionate amount of the angular momentum. Note that the vapor pressure of rock is very, very low, not zero.

 

[steve_bank]

Again a question of immeasurable small changes.

What happens when the mass of a space probe leaves the Earth?