L2 : Point, Line Segment, Ray,Angle - Lines and Angles , Maths, Class 7 Video Lecture - Class 7 | Best Video for Class 7

hello friends this video on lines and
angles part 2 is brought to you by exam
for calm no more fear from exam so as I
said line segment line 3 angle these are
the basics of geometry and definitely
not to forget the most basic element
that is a point so let's start with the
point point is the most fundamental
object of geometry with no length width
or height so it has no dimension less it
has no dimension basically they you just
cannot measure its length or length or
height it is represented by a dot so you
take a pencil and touch the tip of the
pencil on a white sheet of paper what do
you get on the sheet of paper you see a
black dot
so that dot represents a point so think
of a tip of a pencil or the tip of the
compass so these represent dots in fact
there are certain things in nature where
you can visualize dots for example you
are in an aeroplane
now when the flight lands just before it
lands when you look at a city let's say
that you are traveling to New Delhi
ok now the moment a couple of minutes
before if the flight is going to land on
New Delhi and when you try to look from
the window of the flight what do you see
you tend to see everything on the
streets of that city seems like points
so the vended roads or the remnant
vehicles
everything the huge vehicles also they
appear to be points so when you look at
it look at it from a very far distance
all the things whether it is a very good
or it is a streetlight Auditors a
building all of them appears as dots so
these are points similarly when you look
at a star studded sky at night you do
you get to see the exact shape of the
stars no that's because they are very
far away from us so we do see them
twinkling but when you look at them you
they appear to be like dots they
appearance
points that's because we are looking at
them from a very far distance so this is
point the next one is line so line is a
combination of points that extend
indefinitely in both directions so it
will tend to continue infinitely in both
directions this is important about line
so it is nothing but a lot of poems put
together one after another such that it
extends in both direction infinitum
so that's a line so when you think of
lying you can think of the railway lines
that will be track so you know it kinds
of extends infinitely we do not know
till where it extends so so that's an
example of line so a straight angle
always often represented like this with
arrow on both ends which shows that they
are extending in both directions now it
is not necessary that line always has to
be a straight line it can be a curved
line as well because in the definition
nowhere we say that the point should
form a straight line so it is just a
combination of points such that it
extends in both directions so even in
case of a curved line it can extend in
both directions and it is still a
combination of points therefore it is
also a line now
but many times people feel like but if
we talk about the line we are basically
talking about the straight line but
that's really not necessary it can be a
straight line it can also be a curved
line a line is normally represented
let's say that AB strip the straight
line is named as a B so how do we
represent the straight line we write it
as a B and over a B we give the symbol
which shows that this is a line next is
line segment so line segment as the name
suggests it is a segment of the line it
is a part of a line with fixed end
points because in case of line it in M
it doesn't have any end point because
the end it is extending infinitely so
there is no end point but when you talk
about a line segment it is a part of
that same line but it has fixed end
points so let's say that this is the
straight line as we see it it is
extending in both directions now if we
consider two fixed points a and B so
this a B a B is a portion of the same
straight line but this a B has two fixed
end points a and B so a B is a line
segment
so that's line segment now if let's
think of this game which you am sure
you'd have played with your friends now
what happens in this game you have two
teams and both the teams they try to
pull the rope in their own direction
right now when you look at this whole
rope it's like very long right but then
you look at a portion of this rope maybe
only from this part to this part what is
this this this portion is nothing but
the line segment because it is part of
that and big group right so that means
it is a line segment so nine segments is
basically part of a line which has fixed
end points let us look at some examples
of line segments from our day to day
life when you look at the ruler or the
scale its line segment because it has a
fixed length so you know its endpoints
you think of the rope you tie between
two pillars in order to drive your
clothes so here also it notice the fixed
length you know the end points so these
are the two end points therefore this
also a line segment you think of your
textbook or your notebook where you have
these lines so those lines also have end
points of its line segments one simple
exercise that you can do anytime is you
take a sheet of paper just fold it and
then you know try to straighten it again
what do you see you see that a line is
formed here like this like how you see
here so this shows of folding papers
when you fold a piece of paper a line is
formed along those folds so that's all
a line segment because it has fixed end
points so these are the beginning the
ladder that you see on the screen here
also each part is each segment is a line
segment because they have their fixed
end points so these are all examples of
line segments from our day to day life
so I guess that now when you look at
things from juice you'll be able to find
out we're going to see line segments
next is the Ray it is a part of a line
with fixed starting point and extending
endlessly so let's now talk about today
so it ray is also a part of a larger
straight line segment but in this case
it has only one fixed starting point and
it extends endlessly on the other side
that means only one fixed point so when
you represent a ray it is something like
this this end is fixed but this end
extends infinitely so it is like an
intermediate between line and line
segments line extends in both directions
line segments both fixed points ray one
fixed point and one side extending
infinity so the examples of Ray would be
the sun rays light coming from the Sun
so since the source is fixed therefore
one end is fixed but the other end it
reaches infinitely to any place
similarly the light coming out of the
torch that also is an example of a ray
because you have one end fixed which is
the torch and the other end is reaching
out infinitely now the next geometrical
element we will talk about this angle
now what will you see on the screen you
see a boss which is initially closed and
then which is gradually getting opened
and then it is totally opened so how
does this relate to angle of course it
does because angle is nothing but
measure of orientation between two rays
with a common endpoint now here do you
see any sort of Orion
these diagrams so when you look at it
initially you see that the lead is
closed so the lead and the box
they were like oriented along each other
so that's when it was closed in the next
scenario you see when you gradually
start opening it there is some sort of
orientation between these stories this
is one way this is another way and this
orientation is nothing but angle and if
you look at it this way and this area
both of these has a common endpoint
similarly as the box is totally opened
that have been increased on the moon so
basically what Google is angle is a
measurement in degrees which just tells
us how much is the orientation between
two rays so let us look at it
diagrammatically now in the first
scenario what happens is both the Rays
are lying around each other so the angle
is zero Degree in the second case there
is some sort of orientation between the
plume surfaces so here the angle is let
us assume that the angle is say 60
degrees in the third case you see it has
opened all the modes so the angle has
increased so let's say that the value
now is 1 in 120 degrees so what is
happening as the box is gradually
opening the outer is also increasing so
this this is what angle is angle is
about orientation between two rays right
and this is how we represent angle in
the diagram so it is represented by two
rays such that they have a common
endpoint only if they have a common
endpoint they can form an angle
otherwise let's say you have one way
like
like this so there is no common endpoint
so obviously there can be no orientation
between living so when you talk about
the parts of an angle 2 and angle
consists of the sides or arms of the
angle so these are the arms this is one
arm and this is another arm so these are
the arms or sides of the angle and this
common point is on the vertex so once we
have had a quick recap of the basics let
us now talk about related angles now
related angles what do you see on the
screen you see the picture of this
puzzle which see is that the two puzzles
are such that they exactly fit into each
other so similarly we will talk about
angles which are in sum or the other way
degree related to each other thank you
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