Science SPORE Prize
November 2011

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

## User Comments on Tracker Video Analysis and Modeling Tool (7)

### tracker not really accurate

Author: andrew rowney
Posted: January 24, 2014 at 6:18AM

Hi Guys.. i am tearing my hair out to get a motion analysis program which can give 9.8 m/s2 for a falling ball????? tracker gives about double that value ..can anyone help
thanks
andrew

### Re: tracker not really accurate

Author: Wolfgang
Posted: Feb 09, 2017 at 3:23PM

### How acceleration is calculated by tracker

Author: Eran Grinvald
Posted: October 27, 2014 at 5:33AM

I'm a physics teacher in highschool Israel and a part time researcher in the Weizmann Institure of Science. I'm new to tracker and think it is a fantastic tool and very excited about it.

I have two students which are frustrated that they can't reproduce the estimated acceleration calculated in tracker from the raw data (x,y,t) themselves, while they reproduce perfectly the velocities. I tried several algorithims I could think of to calculate the acceleration, all give quite different results, which means that for the specific object we tracked the time interval of the video is not short enough for numerical convergence. Yet non of the algorithims I tried did not reproduce the tracker result.

I could not find anywhere how tracker calculates the x (y) acceleration at a specific time, this without looking at the code itself.

Can anybody tell me what is the formula to calculate the acelleration in the x direction of point N (The first point that tracker calculates for is N=3, as a function of the data set x(i) and t(i) I think the standard algorithim for numerical second order integration can calculate for N=2 as well.)

Eran

### Re: How acceleration is calculated by tracker

Author: Wolfgang
Posted: Feb 09, 2017 at 3:20PM

> On Oct 27, 2014, Eran Grinvald posted:
>
> I'm a physics
> teacher in highschool Israel and a part time researcher
> in the Weizmann Institure of Science. I'm new to tracker
> and think it is a fantastic tool and very excited
>
> I have two students which are frustrated
> that they can't reproduce the estimated acceleration
> calculated in tracker from the raw data (x,y,t) themselves,
> while they reproduce perfectly the velocities. I tried
> several algorithims I could think of to calculate
> the acceleration, all give quite different results,
> which means that for the specific object we tracked
> the time interval of the video is not short enough
> for numerical convergence. Yet non of the algorithims
> I tried did not reproduce the tracker result.
>
> I could
> not find anywhere how tracker calculates the x (y)
> acceleration at a specific time, this without looking
> at the code itself.
>
> Can anybody tell me what is the
> formula to calculate the acelleration in the x direction
> of point N (The first point that tracker calculates
> for is N=3, as a function of the data set x(i) and
> t(i) I think the standard algorithim for numerical
> second order integration can calculate for N=2 as well.
>
>
>
> Eran

### Re: How acceleration is calculated by tracker

Author: Wolfgang
Posted: Feb 09, 2017 at 3:22PM