# Animated horizontal chord of circle

Anthony Vasaturo shared this question 4 years ago

Hello! I'd like to create and export an animation of a chord in a circle that starts as the full horizontal diameter of a circle with radius 2 (so, a length 4 horizontal chord), and ends below itself as a horizontal chord with length 2. It seems that the best way to do this would be to attach two points to the circle at either end of the horizontal equator, and animate them both, the leftmost one counterclockwise, and the rightmost one clockwise.

I only know how to animate single points on a circle, but not two simultaneously, and I also don't know how to make the points stop moving once the chord length has decreased from 4 to 2.

What is the best way to do this?

1

I think 2 sliders, ther works in the same time is not a good idea (except the slides are completely independent).

Instead animate one of the 2 points and construct the dependent point as following:

Reflect(<animatedPoint>, PerpendicularLine(<circleCenter>, xAxis))

.

Construct the animated point not direct on the circle. Construct him on a CircularArc(). Then its possible to control the animation (Start, End, Direction, Speed) with the properties (Algebra) of the animated point.

.

Note the details in the Construction-Protocol in the attachment. Maybe you must consult some explantation in the manual for some commands.

Especialy note the properties of point E / Algebra (Speed, Direction)

.

You can start the animation manual:

• move point E to B
• right-click of point E and start animation

or with the script in button1.

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