# Pull force in NON-EQUILIBRIUM MD
**URL:** https://gromacs.bioexcel.eu/t/pull-force-in-non-equilibrium-md/8699
**Category:** User discussions
**Created:** [March 26, 2024, 3:31pm UTC](https://gromacs.bioexcel.eu/t/pull-force-in-non-equilibrium-md/8699 "2024-03-26T15:31:22Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@roozi](https://gromacs.bioexcel.eu/u/roozi)
#### Post date: [March 26, 2024, 3:31pm UTC](https://gromacs.bioexcel.eu/t/pull-force-in-non-equilibrium-md/8699/1 "2024-03-26T15:31:22Z")
GROMACS version:2024
GROMACS modification: no
Hi
I just want to make sure that the pull force in non-equilibrium md simulation output reported by gromacs pull code (pullf.xvg) is the applied force exerted BY the spring on the pull group ATOMS and not the force ON spring due to pull group atoms. Am i right?
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### Author:  [@roozi](https://gromacs.bioexcel.eu/u/roozi)
#### Post date: [March 27, 2024, 10:03pm UTC](https://gromacs.bioexcel.eu/t/pull-force-in-non-equilibrium-md/8699/2 "2024-03-27T22:03:37Z")
i will appreciate if some one with knowledge of gromacs internal woks or from developers team, could answer my question.
B/R
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### Author:  [@hess](https://gromacs.bioexcel.eu/u/hess)
#### Post date: [March 28, 2024, 1:58pm UTC](https://gromacs.bioexcel.eu/t/pull-force-in-non-equilibrium-md/8699/3 "2024-03-28T13:58:24Z")
That depends on how you have selected your pull groups in the pull coordinate. It is the force exerted by the spring on the second group.