3

Does a place without force exsist, if it so where or how could it be. I mean if we include Gravity and friction as our force in universe.

Fellas21
  • 49
  • 3
    Gravitational force is basically infinite in range (see this NASA Q&A), so there won't be such a point. However, between galaxies, the gravitational force of those galaxies would be small. – Kyle Kanos Apr 23 '19 at 11:39
  • Do you mean places where forces exist but is cancelled/balanced? – Qmechanic Apr 23 '19 at 11:44
  • 1
    Are you also including the other three fundamental forces? If so, you would therefore be looking for a place in the universe where there’s neither light nor matter... – Chappo Hasn't Forgotten Apr 23 '19 at 13:02
  • If there would be such a place I assure you I could create infinite energy by just rotating a rod and connencting it to a generator , turbine etc. – Aditya Garg Apr 23 '19 at 14:54
  • @Aditya Garg But if the motor effect didn’t oppose the motion of your rod, then you couldn’t do work against it. and I thought if you can’t do work against the motor effect you couldn’t induce voltage. – Hisham Apr 24 '19 at 11:15
  • @Aditya If that's supposed to be a joke, I don't get it. – PM 2Ring Apr 25 '19 at 01:49
  • @KyleKanos The effect of gravitation would always be present (the curvature tensor) but the force (the Christoffel symbols) can be made to vanish at wish, right? So, a free falling frame inside an ideal Faraday cage would be the kind of place the OP is asking for maybe? –  Apr 25 '19 at 01:58
  • I would say the area with the least gravity would be the Bootes Void... there are stars and galaxies there, but the is not as much as the rest of the universe (at least that we can see) – Rick Apr 25 '19 at 02:03

3 Answers3

1

Sadly, there is no place in our present observable universe which doesn't experience at least one type of force. Why? Because our universe has plenty of stuff in it (mass, charge, energy,...). And all of them interact with each other in some way or the other. Gravitation, coulombic attraction, and many others. The cool part about all these interactions/forces is that they act in a continuous manner.

What I mean by that is the forces don't abruptly cease to exist if you move an object some place else. Take, gravity, as an example. If you keep any two bodies 1 m apart, they attract. Move them further apart, they still attract. A little bit more, they still attract. The force reduces for sure, but it's still there. No matter how far apart you keep them, they will still attract. You can make that force extremely small, almost unnoticeable, by keeping them a trillion miles apart, but it's still there. Never $0$.

One can see this mathematically, by arguing that gravitational force, given by the inverse square law, is a continuous function, so force will always exist.

But that isn't a big problem. It's because our universe is huge. So huge infact, that there are plenty of places where you could do experiments without almost any interference from external forces. This is because if your location is decently far away from everything else, the external forces become extremely small. So small indeed that their effect on your experiment can be completely neglected. So most of the times, it's alright with everything not being perfectly $0$. Approximations are good too!

Hope this helps.

PM 2Ring
  • 11,873
Apekshik Panigrahi
  • 652
0

Gravitation is not a force. Our planet, the stars or a satellite, all they are following their geodesic paths. Even if an object is falling towards the moon, it is weightless and follows its geodesic path. Only the acceleration during the crash on the moons surface is due to a force.

With regard to friction, it's not that simple. The geodetic paths are different with respect to the initial velocities. Dust and gases, molecules and conglomerates flow through the universe at different speeds than your specimen. That influences and changes the calculated geodesic path.

Which place in the universe that does not have force at all?

The Outer space is the best place. If it is to far away, the ISS is a good place to do experiments. Cheaper it is to use a Drop tube.

HolgerFiedler
  • 10,334
  • Gravitation is a force. Just because we can explain the reasoning behind the origin of a force in greater details doesn't mean that it no longer remains a force. See this comment by Lubosh Motl: https://physics.stackexchange.com/questions/33875/gravitation-is-not-force#comment74668_33875 –  Apr 25 '19 at 02:01
  • @DvijMankad https://physics.stackexchange.com/a/33927/46708 ;-) – HolgerFiedler Apr 25 '19 at 05:07
0

It depends how you define "place". Because there is not a fixed "background" inertial frame, if you pick a point you also need to pick an inertial frame. That is, you need to specify how that point is moving with respect to everything else.

It also depends how you define "force". Normally, "force" is related to acceleration of a test particle.

Acceleration of the test particle is conceptually easy to measure by using an "instrumented test particle": put tiny gyroscopes and spring-and-mass accelerometers on the particle and read their outputs. It turns out that if you do this (mathematically feasible but practically very difficult) with a free uncharged test particle, it will report zero acceleration regardless of its initial motion and location because it will be in free fall - zero g.

However, if the same thing is done using a charged test particle, the instruments on the particle will not always report zero acceleration. If there is an electromagnetic field present, the particle will experience Coulomb and Lorentz forces. Unless all of the components of the tiny gyros and accelerometers are made of components with exactly the same charge-to-mass ratio as the test particle (which is not even theoretically possible), they will not experience the same forces as the particle and will therefore report that there is acceleration.

So: using the "instrumented test particle" method described above to define "force", and defining "place" as "local inertial frame", it is fair to say that there are places in the universe where an arbitrary test particle experiences no force: those places where the electromagnetic field is exactly zero. In a universe where everything is constantly moving, those places will exist only for brief moments for any particular test particle.

S. McGrew
  • 24,774