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November 2019

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November 2011

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## Take-off velocity and take-off angle post and replies

take-off angle
4 Posts

Hey guys.

I'm doing a monograph project on frog jumping system. So I filmed the jumps in a lateral view and now I need to get some variables like the take-off angle. However, I am having trouble figuring out how to do this. Just to clarify, the take-off angle is the angle formed when the animal's last toe moves off the ground in relation to the horizontal line.

So,I tried using the angle of position and the protractor, but I don't know if it makes sense. Follow the photo below.

Any thoughts or suggestions would be most welcome.

My thanks,

Vitor.

Attached File: tracker4.jpg

### Replies to take-off angle

Re: take-off angle -

Douglas Brown
339 Posts

From your photo its hard to see where the frog and toe are. What exactly have you tracked with massa A--the toe? The 40.6 degree angle is the angle between the position of the track and the origin of the coordinate system, but the origin doesn't appear to be on the ground. Also, neither of your plots show data from the protractor and you don't need the protractor if you want the angle relative to the horizontal axis. Can you give us more info?

> Re: take-off angle
>
> Hey guys.
>
> I'm doing a monograph project on frog jumping
> system. So I filmed the jumps in a lateral view and
> now I need to get some variables like the take-off
> angle. However, I am having trouble figuring out how
> to do this. Just to clarify, the take-off angle is
> the angle formed when the animal's last toe moves
> off the ground in relation to the horizontal line
>
>
>
> So,I tried using the angle of position and the
> protractor, but I don't know if it makes sense. Follow
> the photo below.
>
> Any thoughts or suggestions would
> be most welcome.
>
> My thanks,
>
> Vitor.

Re: take-off angle -
4 Posts

Hi Doug! Thank you very much for your reply, I appreciate it.

So, in mass A, I tracked exactly the animal's girdle, standardized this marking location for all videos.

And, the origin of the coordinate system is just below the animal, in the ground.

The question on the animal's finger is just for me to know the exact frame in which the animal left the ground, so I can set the frame to calculate the angle. it's not really good to check exactly when the animal's finger leaves the ground, but I can get a sense of it when I'm passing the frames.

So I think this is the angle I really need. Just to clarify, does the "position angle" variable tell me the angle formed between the mass I tracked and the origin of the coordinate system?

Re: take-off angle -

Douglas Brown
339 Posts

Hi Vitor, thank you for clarifying. I think you are doing the right thing: yes, the "position angle" variable is the angle of the line from the origin to the track position, measured counterclockwise from the x-axis.  Doug

Re: take-off angle -
4 Posts

Thank you so much for clarifying my question !!

If it doesn't bother you, I have another question.

the variable "v: velocity magnitude" shows me the result of velocities x and y? Because in my videos, I have both the velocities on the x-axis and the y-axis, so I would need the resulting velocity to know the exact speed of the animal. So, i would like to know if this variable "velocity magnitude" already shows me the resulting of x and y or if I need to do some calculation to know the resulting velocity.

Re: take-off angle -

Douglas Brown
339 Posts

Hi Vitor, yes the velocity magnitude, also called speed, includes both x- and y-axis motion.

Re: take-off angle -