Rotation - of a polygon
From Latin: rotare - "revolve, roll"
A transformation where a figure is turned about a given point.
Try this Drag any orange dot to move P, the center of rotation. Drag the polygon to rotate it about P.

The "rotation" transformation is where you turn a figure about a given point (P in the diagram above). The point about which the object is rotated can be inside the figure or anywhere outside it. The amount of rotation is called the angle of rotation and is measured in degrees. By convention a rotation counter-clockwise is a positive angle, and clockwise is considered a negative angle.

Rays from the point of rotation to any vertex all turn through the same angle as the image is rotated. Click on "show rays" and rotate the image to see this.

Things to try

In the diagram above - click 'reset'
  1. Rotate the polygon by dragging anywhere inside it. Note how it rotates about the point P.
  2. Drag the the point P inside the polygon. Now when you rotate it, note how it turns around the point P as if P was a pin holding it to the screen.
  3. Rotate the polygon a full 360° and note how it is now back to its original position.
  4. Click "hide details". Then rotate the polygon to some new position and estimate the angle of rotation. Click "show details" to see how close you got.

Other transformation topics


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