# yade-users team mailing list archive

## [Question #697877]: unexpected Plot of normal force

```New question #697877 on Yade:

Here is my simulation
I have placed a sphere on a horizontal wall. A normal force is applied on the sphere vertically downward. Some velocity is given to the plate.

Now I am recording normal force on sphere vs displacement of plate graph.
Here I am expecting a constant value of normal force on sphere but Yade returns an abrupt behaviour in starting , however it is constant thereafter but with some different magnitude.
I have not used force resetter as it makes the graph periodic and gives unwanted results.

Kindly help us with how we can plot the actual normal force which is given initially on the graph.

sp=sphere((0,0,0),1,material=MaterialS)  #creating sphere
plate=utils.wall(-1,axis=2,material=MaterialP) #creating plate
plateID=O.bodies.append(plate)  #plateID=0
spID=O.bodies.append(sp) #spID=1
O.forces.setPermF(1,(0,0,-4))  # 4 mag. force on sphere in -ve z direction
plate.state.vel =(0,1,0)  #plate given const. velocity in y direction
O.engines=[
#ForceResetter(),
InsertionSortCollider([Bo1_Sphere_Aabb(),Bo1_Wall_Aabb()]),
InteractionLoop(
[Ig2_Wall_Sphere_ScGeom()],
[Ip2_FrictMat_FrictMat_FrictPhys()],
[Law2_ScGeom_FrictPhys_CundallStrack()]
),
NewtonIntegrator(gravity=(0,0,0),damping=0),
]

#if O.iter<10000:
#plot.plots={'Displacement':('FrictionForce')}
plot.plots={'Displacement':('NormalForce')}
plot.plot()
O.dt=.5e-4*PWaveTimeStep()
O.saveTmp()

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