# Roll out a circle or an arc

- Author:
- Linda Fahlberg-Stojanovska

Unroll the circle) to see how long its circumference is.
Use the sliders to:

*r*: Change the radius- α: Unroll only an arc of the circle by changing the number of degrees to unroll
*t*: Manually control the unroll.

What is the exact length of the circumference of a circle of radius R=1? What is an approximate value to 2 decimal places?
Why does it look like the grid is not square? What is an approximate value of ? Is the grid square 1:1?
What is an approximate value for the length of the arc for 270° for a circle of radius R=1.5?