# VR

Returns the relative velocity of marker I with respect to J. Time derivatives are computed in the reference frame of marker L. Markers J and K are optional.

VR(I, J, L)

## Arguments

I
The marker whose velocity is to be computed.
J
The marker with respect to which the velocity is to be computed. If omitted, it defaults to the ground coordinate system.
L
Time derivatives are taken in the coordinate system of this marker. If omitted, it defaults to the ground coordinate system.

## Example

<Force_Scalar_TwoBody
id             = "101001"
type           = "Force"
i_marker_id    = "10508"
body1_id       = "105"
j_marker_id    = "10307"
body2_id       = "103"
val_expression = "100-0.1*VR(10508,10307)"
/>