Rotational symmetry

In your book, Maths Mela (Chapter 10), Lali makes paper windmills, called firkis, for her friends. She marks a dot on one blade so we can keep track of it. Then we turn the firki by 1/4 of a turn, 1/2 a turn, 3/4 of a turn and a full turn. After each of these turns, the firki looks exactly the same as at the start: the dot has moved to another blade, but the shape is the same.

A shape has rotational symmetry if it looks the same after LESS than a full turn. Every shape looks the same after a full turn, because it is back where it started, so a full turn does not count. The firki has rotational symmetry: it looks the same after 1/4, 1/2 and 3/4 of a turn.

Now take the capital letter H. After 1/4 of a turn it is lying on its side, with its two long bars lying flat, so it does not look like an H. After 1/2 a turn it is upright again and looks exactly like an H. After 3/4 of a turn it is lying on its side again. So the letter H has rotational symmetry, at 1/2 a turn.

Not every shape has rotational symmetry. Turn the capital letter A by 1/2 a turn and it is upside down, with its point at the bottom. After 1/4 or 3/4 of a turn it lies on its side. It looks like an A again only after a full turn, so the letter A has no rotational symmetry.