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Physics of a Gas Pressure Gauge

Ranges of barometer liquid heights are very small, typically less than 10%. In order to have more range for the applied pressure, I have chosen to name it a liquid pressure gauge instead of a barometer. The principle of operation is exactly the same.

Description of Device Graphics

The pressure gauge has both a column of liquid and a vat containing the same liquid. The pressure gauge vat and column are surrounded by a gas whose density and average energy is adjustable. The gas and the gauge are in a sealed container. To initiate the liquid column, the empty column tube is evacuated while its bottom is in the vat and the gas pressure is relatively low. The gas pressure then causes the liquid in the column to rise. The liquid should have reasonably high density and a low vapor pressure at room temperature. Often mercury is chosen for the liquid. The number of surrounding atoms can be increased and their speed can be increased by heating. For a simple explanation of the physics of a barometer which is similar to this device see Liquid Barometer Discussion.

Viewing the Results

A plot of the average force on the vat surface is provided. If the viewer changes either slider setting, the plot value will change accordingly.

Data

Appendix:Boundary Collision Analysis

I've been having some problems with collisions of hard spheres of radius `r` with simple boundaries. The parameters involved are the position, `u_b`, of the boundary, the position, `u_s`, of the sphere center, the speed, `v_u` of the sphere and the the time, `t_f`, between position and velocity updates (frame time). In cartesian coordinates, `v_u=v_(x,y,z)`, `u_b=(x_b,y_b,z_z_b)`, and `u_s=(x,y,z)`. So the update program can be the following

Both distance and speed have to be positive
`t_c=|(u_b-r)-u_s|/|v_u|`
if `(t_clt=t_f)`

if there is a turn around then the velocity component is negated
`v_u'=-v_u`
`u_s` turns around and its center continues by distance `v_u'(t_f-t_c)` away from `u_b`.
`u_s'=v_u'(t_f-t_c)+r*"sign"(v_u')`

or else `u_s'=u_s+v_ut_f`

Obviously the previous algorithm does not usually result in an exact wall hit but it does result in a virtual wall hit. For general step sizes `delta_(u_s)=v_ut_f` and general sized containers there will never be wall hits. However, for moderately small values of `v_ut_f` compared to container size, this will not substantially affect the phical results.