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I have read in some textbooks (such as Griffiths' Electrodynamics) that ultimately there are only four forces underlying all physical phenomena: 1) Gravitational 2) Electromagnetic 3) + 4) Weak and Strong Forces. It is then argued that all of those contact forces that we encounter in everyday life, such as normal forces, friction forces, tension forces, drag forces and push and pull forces are ultimately electromagnetic in nature.

So I am wondering: How is a setup such as me pulling on a rope attached to a cart an electromagnetic process? I found some useful explanations here:

Conceptual doubt in Tension force

But it raises another question for me: What about the pull that I exert on the rope, or on the "initial" molecule on the rope? How is that electrical in nature? And what about the rope pulling the cart?

Also, say I lift a mass from the ground by grabbing it and lifting it: How is that electrical in nature?

I hope someone can bring some light into this!

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  • $\begingroup$ Small note: you've got the boundaries between the forces a bit wrong. It's 1) gravity 2) and 3) Electromagnetic + weak 4) Strong nuclear force. that is, The weak force is in some sense much more similar to the EM force (they are the same at high enough energy). en.wikipedia.org/wiki/Electroweak_interaction $\endgroup$
    – Metropolis
    Commented Jun 24, 2021 at 18:48

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Everything we experience regarding pushes and pulls in our (macroscopic) world ultimately originates on the microscopic level of atoms and molecules pressing up against one another or being pulled apart from one another. The manner in which those pushes and pulls get exchanged occurs by the interaction of the outermost electrons in the electron clouds that surround those atoms and molecules.

So when you push your fingertip against the surface of a key in your computer's keyboard, the electron clouds surrounding the skin molecules in your fingertip are pushed up against the electron clouds surrounding the plastic molecules in the key surface, and the fingertip push gets transmitted into the key body and thence into the spring under the key, the PC board under the spring, the board standoffs molded into the bottom case, the rubber feet near the standoffs, the tabletop under the feet, etc., etc.

Alternatively, the pull on one end of a rope tries to separate the cellulose molecules that the rope fibers are made of and the electrostatic forces of attraction present between the electron cloud of one molecule and the nucleus of the next one over transmit the pull tension from one molecule to the next, and the next, and so on.

In this sense, electrostatic forces of attraction and repulsion on the micro scale are responsible for the transmission of compression and tension forces in the macro world.

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Everything is made up of atoms (in our context) of elements. Atoms interact with each others to form molecules or lattice. This interaction is almost purely electromagnetic in nature.

When you pull a string, at atomic scales, an atom is pull its neighbour atom using electromagnetic interaction.

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