What is a Polyhedron and its Types? Video Lecture - Class 8

good morning children today we shall
learn what is a polyhedron
but first water solids the pencil box
the ball the birthday cap dies and the
dustbin all are solid shapes all the
solid shapes which we can hold have one
more dimension which is the depth like
this dies it has the length breadth and
the depth all the solid objects are 3d
shapes 3d means three dimensions length
breadth and the depth so this is a dice
and the solid shape is called cube in a
cube the length breadth and the depth
all are same as a cube has six surfaces
we can say a cube has six faces and each
face is a square you know certain 3d
shapes have curved edges like the
cylinder or the cone also if you notice
not all the faces are similar in both of
these a cylinder has three faces out of
which two are circular faces and coming
to the coal in the coal one of the faces
is circular so we can say in some of the
shapes the faces are not similar you
know a solid shape with flat faces and
straight edges is called a polyhedron so
this prism and the pyramid and the cube
are polyhedrons or polyhedra which is
the plural of polyhedron if you remember
the polygons are the 2d
shapes which are closed figure and made
of line segments like the square the
rectangle the triangle etc so we can say
a polyhedron is a 3d shape with polygon
faces so cube prism pyramid etc are
polyhedron with each face being a
polygon look here these 3d shapes have
curved edges and even their faces are
not similar hence we can say these are
not polyhedrons or polyhedra the plural
of polyhedron if we observe few
polyhedra have same kind of faces like
this Q in the cube each face is a square
so we can say all the faces of this cube
are congruent here again in this
triangular pyramid each face is an
equilateral triangle which means all the
faces of this pyramid are congruent
if you remember the regular polygons are
the 2d shapes which are closed figure
with all sides equal like the square the
Pentagon with all the five sides equal
equilateral triangle with three sides
equal etc so we can say the polyhedra
like the cube or this triangular pyramid
where all the faces are congruent and
regular polygons that is polygons with
equal sides are called
regular polyhedra so we can say a
regular polyhedra has all the faces
which are congruent regular polygons you
know this cube is also called a regular
hexahedron as it has six equal faces so
regular hexahedron same way this
triangular pyramid is called a regular
tetrahedron as it has four equal faces
so what about a regular polyhedron if
all the faces of a solid shape are not
same or equal like here there is a
pyramid it has a rectangular base but
triangular side faces so we can say this
rectangular pyramid is an irregular
polyhedron as the faces are not
congruent or same to sum up what we
learn today what is a polyhedron in
short it is a 3d shape with polygon
faces meaning it is a 3d shape where
each face is a polygon that is each face
is flat with straight edges and what is
a regular
polyhedron a polyhedron with all the
faces as congruent regular polygons
meaning all the faces are of same type
of regular polygons is called a regular
polyhedron and lastly what is an
irregular polyhedron a polyhedron in
which all the faces are not same meaning
they are not the same type of polygons
is called an irregular polyhedron that's
all for now bye bye children