Ch-9
Symmetry and Nets of Solids.

•    Reflection means seeing the image of something in a mirror.
•    A line of symmetry is a line that cuts a shape exactly in half.  
•    This means that if you were to fold the shape along the line, both halves would match exactly. Equally, if you were to place a mirror along the line, the shape would remain unchanged. 
•    Reflection symmetry is when a shape or pattern is reflected in a line of symmetry / a mirror line. The reflected shape will be exactly the same as the original, the same distance from the mirror line and the same size. 
•    Rotation in symmetry- A shape has rotational symmetry when it can be rotated and it still looks the same.
•    The order of rotational symmetry of a shape is the number of times it can be rotated around a full circle and still look the same
•     Three things are needed to describe a rotation that are:- 1) Direction of Rotation   2) Angle of Rotation   3) Centre of Rotation.
•    Center of rotation = For a figure or object that has rotational symmetry, the fixed point around which the rotation occurs is called the centre of rotation. Example: the centre of rotation of a windmill in the centre of the windmill from which its blades originate.
•    Angle of Rotation =For a figure or object that has rotational symmetry, the angle of turning during rotation is called the angle of rotation. Example: when a square is rotated by 90 degrees, it appears the same after rotation. So, the angle of rotation for a square is 90 degrees.
•    Direction of Rotation = Rotation may be clockwise or anticlockwise.
•     If, after a rotation, an object looks exactly the same, we say that it has a rotational symmetry.
•    In a complete turn (of 360°), the number of times an object looks exactly the same is called the order of rotational symmetry. The order of symmetry of a square, for example, is 4 while, for an equilateral triangle, it is 3.
•    An object has rotational symmetry if there is a centre of point which if the object is rotated or turned a certain number if degrees and the object still looks the same. 
•    Order of Rotational Symmetry= The number of positions in which a figure can be rotated and still appears exactly as it did before the rotation, is called the order of symmetry. 
•    Full turn=360°  ; ½ turn=180°   ; ¼ turn=90°
•    Order of rotational symmetry of Square is 4.
•    Order of rotational symmetry of Rectangle is 4.
•    Order of Rotational symmetry of an equilateral triangle is 3.
•    A circle have infinite order of rotational symmetry as a circle will always fit into its original regardless of how many times it is rotated.
•    Plane of symmetry=  a plane or a surface l that divides the solids into two parts that are mirror images of each other or identical halves.
•    The figure has two lines of symmetry: the horizontal line of symmetry cuts the figure into a top and bottom that are mirror images of each other; the vertical line of symmetry cuts the figure into a left and right that are mirror images of each other. 
•    A cone and a sphere have infinite number of planes of symmetry.
•    A net can be folded up to make a 3D shape.
•    There may be several possible nets for one 3D shape.
•    The net of a cube and a square based pyramid.

*WRITE PG. NO. 147 ALSO. SAME AS GIVEN IJ BOOK ALONG WITH DIAGRAMS.

8.jpeg
9.jpeg
10.jpeg
11.jpeg
WhatsApp Image 2021-06-29 at 20.48.27.jpeg
WhatsApp Image 2021-06-29 at 20.48.28.jpeg
WhatsApp Image 2021-06-29 at 20.52.08.jpeg
WhatsApp Image 2021-06-29 at 20.48.28 (1).jpeg
1.jpg
2.jpg
3.jpg
3.jpg
4.jpg
5.jpg
6.jpg
7.jpg
8.jpg
9.jpg
10.jpg
11.jpg
12.jpg
CamScanner 05-03-2021 07.48_1.jpg
CamScanner 05-03-2021 07.48_2.jpg
CamScanner 05-03-2021 07.48_3.jpg
CamScanner 05-03-2021 07.48_4.jpg
CamScanner 05-03-2021 07.48_5.jpg
CamScanner 05-03-2021 07.48_6.jpg
CamScanner 05-03-2021 07.48_7.jpg
CamScanner 05-03-2021 07.48_8.jpg
CamScanner 05-03-2021 07.48_9.jpg
CamScanner 05-03-2021 07.48_10.jpg
CamScanner 05-03-2021 07.48_11.jpg
CamScanner 05-03-2021 07.48_12.jpg
CamScanner 05-03-2021 07.48_13.jpg
CamScanner 05-03-2021 07.48_14.jpg
CamScanner 05-03-2021 07.48_15.jpg
CamScanner 05-03-2021 07.48_16.jpg
CamScanner 05-03-2021 07.48_17.jpg
CamScanner 05-03-2021 07.48_18.jpg
CamScanner 05-03-2021 07.48_19.jpg
CamScanner 05-03-2021 07.48_20.jpg
CamScanner 05-03-2021 07.48_21.jpg
CamScanner 05-03-2021 07.48_22.jpg
CamScanner 05-03-2021 07.48_23.jpg
CamScanner 05-03-2021 07.48_24.jpg
CamScanner 05-03-2021 07.48_25.jpg
CamScanner 05-03-2021 07.48_26.jpg
CamScanner 05-03-2021 07.48_27.jpg
CamScanner 05-03-2021 07.48_28.jpg
CamScanner 05-03-2021 07.48_29.jpg
CamScanner 05-03-2021 07.48_30.jpg
CamScanner 05-03-2021 07.48_31.jpg
5.jpg
6.jpg
7.jpg
1.jpg
2.jpg
3.jpg
4.jpg