I realize this is a rather deep question (maybe a rather impractical one) but Im wondering why is it that ‘forces’ cause objects to move? Why are the able to push, pull, rotate objects and matter? Have we discovered this? Cheers!
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$\begingroup$ Just to be clear, are you asking why forces between physical objects are possible? Are you asking why, for example, if you try to touch a wall, your hand doesn't simply pass right through? or why, the floor beneath your feet and the ground beneath the floor stop you from falling right through to the center of the Earth? $\endgroup$– Solomon SlowCommented Oct 9, 2022 at 19:04
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$\begingroup$ "Have we discovered this?" It's part of our model of how nature works. $\endgroup$– Weather VaneCommented Oct 9, 2022 at 19:08
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$\begingroup$ @SolomonSlow I guess my question is yes “how” are forces possible and why they move objects/matter $\endgroup$– JakeCommented Oct 9, 2022 at 19:24
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$\begingroup$ Yup, Deep question. @Dale said, "answering a 'why' question requires some sort of deeper principle..." Physics has a problem with "why" questions. You find the deeper principle, but then you want to know why that is true. It's "Why...?" all the way down. If you keep asking why solid objects push against each other instead of just passing through each other, eventually you'll get to this: en.wikipedia.org/wiki/Pauli_exclusion_principle That's where I get off the elevator. I tried to ask why is the Pauli Exclusion principle true, but I am not equipped to understand the answer. $\endgroup$– Solomon SlowCommented Oct 9, 2022 at 22:49
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1$\begingroup$ Force as a concept does not stand on its own. It exists among other concepts such as energy/work, momentum, displacement, power, impulse, etc. So no explanation is going to be complete without a full description of the subject of mechanics. To that end you need to describe your level of understanding of these concepts and maybe focus a bit on what exactly is the problem you are asking. $\endgroup$– John AlexiouCommented Oct 10, 2022 at 4:58
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4 Answers
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In general, answering a “why” question requires some sort of deeper principle or thing that is taken as a given. Physicists like conservation laws (and their associated symmetries) as their deepest principles, so I will take as a given the conservation of momentum (and its associated symmetry).
Momentum is the conserved quantity associated with the fact that the laws of physics are the same everywhere. When you write that down for a standard mechanical system in standard coordinates, you find that the conserved momentum has the form $\vec p=m\vec v$.
Because momentum is conserved it must be transferred from one object to another, and the rate of change of the momentum is called force. Because the momentum $\vec p$ is changing either $m$ or $\vec v$ must change, but since mass is a scalar it doesn’t have enough freedom to produce all possible changes in momentum. So to change $\vec p$ we usually must have $\vec v$ change.
So, a force is a change in momentum which usually happens through a change in velocity and a change in velocity is acceleration. Thus, forces give acceleration.
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This question is hard to answer because it is somewhat abstract - but as I understand, physicists take the 4 fundamental forces of nature (electromagnetism, gravity, strong force, weak force) for granted. We don't know for sure why they occur, but we have fairly good equations for how they work and we use them to predict other kinds of forces. All of the forces that you encounter in daily life (pushing, pulling, twisting, etc.) are just extensions of those fundamental forces, especially the electromagnetic force.
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I think the question is the wrong way to ask.Physisist see that it need something to accelerate a mass. They call this something a force and define it by F=m*a. the other answer gives you the fundamental forces.
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Long before the newtonian formalism of forces was developed to describe the dynamics of objects, we discovered that, one way or another, objects move. Having established this observed fact, Newton postulated that there are these things called "forces" that cause objects to accelerate, and mathematically, the effects of forces are given by $\vec F=m\vec a$. In other words, forces cause objects to move (or to not move) by definition.
As a side note, it is also worth noting that it is entirely possible to do classical mechanics without referring to the newtonian notion of "forces," instead describing interactions using potentials, as is done in the lagrangian and hamiltonian formalisms.
