Science SPORE Prize
November 2011

The Open Source Physics Project is supported by NSF DUE-0442581.

## Variable angle for coordinate system post and replies

Mobile coordinate system - Feb 6 at 5:14AM
Nicolas MALESYS
2 Posts

I use Tracker for my engineering teaching and I need to have a coordinate system with a mobile origin and a mobile axes. The mouvement of solids are simple when we observe them from a near solid (generally, two solids in contacts) but the second one must be in mouvement to.

The first point is simple : uncheck Fixed Origin in the Coordinate menu and choose a point in the Reference Frame menu.
I try to solve the second point : uncheck Fixed Angle in the Coordinate menu, but no option appears to choose 2 points or a tape measure for example.

Somebody helps me about the option Fixed angle ?
Thanks

### Replies to Mobile coordinate system

Re: Mobile coordinate system - Feb 07 10:40AM

Douglas Brown
231 Posts

You're right that there is no way to set the axis angle to automatically match that of a tape measure or other angle. You can set the angle in each frame by tracking (or autotracking) the x-axis "handle" point, but that is not the same as matching an existing track as with the origin.

Has anybody else in this group ever needed this functionality? Does anybody know a way to do this? Doug

> Re: Mobile coordinate system
>
> I use Tracker for my engineering teaching and I need
> to have a coordinate system with a mobile origin and
> a mobile axes. The mouvement of solids are simple
> when we observe them from a near solid (generally,
> two solids in contacts) but the second one must be
> in mouvement to.
>
> The first point is simple : uncheck
> Fixed Origin in the Coordinate menu and choose a point
> in the Reference Frame menu.
> I try to solve the second
> point : uncheck Fixed Angle in the Coordinate menu,
> but no option appears to choose 2 points or a tape
> measure for example.
>
> Somebody helps me about the
> option Fixed angle ?
> Thanks

Re: Mobile coordinate system - Feb 13 3:07AM
Nicolas MALESYS
2 Posts

I'm alone in using Tracker in mechanics (complex systems) ? so I think even if it's possible to integrate this function in Tracker, the demand is not sufficient ...

Look at this example : https://www.4moms.com/mamaroo.

The mechanical system is "complex" and we can analyse the relative movements with tracker (sse attached file).

But in this case, it will be wise to use polar coordinates to analyse positions of points relative to any referential (i.e. moving solid)

Attached File: mobycrea.png

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