1. Lesson 2 Curved surfaces

2. Learning outcomes To be able to identify a chord To be able to identify a chord To describe the pressed screed method To describe the pressed screed method To identify a secant line To identify a secant line

3. Forming accurate curved surfaces requires the same basic principles as running a semi - circular arch. r = 90º A Radius Rod is set across the diameter of the curve,so it has three equal radius measurements as shown (A,B,C). A B C

4. A B C r = 90º The dots are set from a radius rod. A B C The pressed screed method. Dots set from the radius rod and then plumbed up. Screeds between the dots.

5. A B C r = 90º Screeds need to be applied once the dots have set enough and pressed into a curve with the template, hence the name the pressed screed method. This method can also be used to float the interior of a niche.

6. X Y Chords are equidistant from the centre if and only if their lengths are equal. The centre for a concave curved wall can be determined by bisecting two chords A chord of a curve is a geometric line segment whose endpoints X,Y both lie on the curve. Form a concave curved wall Columns Cornices and Curves Chapter 7 page 16 A secant or a secant line is the line extension of a chord A chord of a curve is a geometric line segment whose endpoints X,Y both lie on the curve. A secant or a secant line is the line extension of a chord. X Y Chords are equidistant from the centre if and only if their lengths are equal. Form a concave curved wall Columns Cornices and Curves Chapter 7 page 16 A secant or a secant line is the line extension of a chord A chord of a curve is a geometric line segment whose endpoints X,Y both lie on the curve. A secant or a secant line is the line extension of a chord. X Y Chords are equidistant from the centre if and only if their lengths are equal. Form a concave curved wall Columns Cornices and Curves Chapter 7 page 16 A secant or a secant line is the line extension of a chord A chord of a curve is a geometric line segment whose endpoints X,Y both lie on the curve. A secant or a secant line is the line extension of a chord. X Y Chords are equidistant from the centre if and only if their lengths are equal. A secant or a secant line is the line extension of a chord.

7. Task Sketch a circle and show the chord and secant line Sketch a circle and show the chord and secant line

8. Recap What is the pressed screed method What is the pressed screed method How do we find the cord of a circle How do we find the cord of a circle What is a secant line What is a secant line