Rotational Symmetry, Order and angle of Rotation Video Lecture - Class 7 | Best Video for Class 7

hey guys mr. Baran's here again the
bring you another exciting math video
and I'm gonna talk a little bit today
about rotational symmetry how do we tell
if an object has rotational symmetry and
a couple of other things that go along
with rotational symmetry as well so here
I have some random symbol that I found
and we're gonna rotate it and we're
gonna see if it has rotational symmetry
so let me rotate it and see what happens
so I rotate this around to reach this
point right here or something magical
kind of happens right it sort of looked
exactly like it was from in start I do
the same thing again and it happens
again and again it happens and again
another time and then finally were back
to the start so what we saw there was
that this image as we rotated it around
it coincided with itself several times
so basically if that's a fancy way of
saying is we rotate it around and it
looked exactly like it did when we
started okay so when I rotate it here it
doesn't look any different right here
then it did at the start but I think
okay so the definition of rotation
symmetry in fancy terms is coincides
with itself in a rotation of less than
360 degrees
okay so somewhere between 0 and 360
degrees the object hasn't coincide with
itself the reality is that if it doesn't
do it by 180 then there's a pretty good
chance that's not going to do it okay so
that's rotational symmetry coincides
itself in a rotation of less than 360
degrees a with rotational symmetry there
are a couple definitions that we need to
know in order order of rotation so order
of rotation is basically asking a
question is how many times there's a
coincide with itself so if we look at
this thing we start we got one two three
four five and then back to start sick
my order of rotation simply is equal to
six so hopefully you can visualize in
your mind because you're not going to
have that technology on your test
obviously you'll be able to rotate this
thing but hopefully you'll be able to
visualize in your mind on how to rotate
this object so just visualize that
you're actually taking it and turning it
and if need be use some tracing paper if
you have to and the last thing we'll
talk about in this video is angle of
rotation so what's it mean for for
what's it mean angle of rotation angle
of rotation simply it's defined by this
formula it's 360 degrees divided by six
so if we do that calculation my angular
rotation is 60 so it's the time it takes
to do or sorry the one full rotation 360
degrees divided by the order of rotation
six and we can sort of see that where
that comes from if we rotate this object
a long time we rotate it from here to
here we see that the angle of rotation
simply how long does it take for the
object phone aside from so far how much
of a rotation does it take for the Apple
inside with itself so we see that this
object from here to here I rotate it
it's 60 degrees and that's it another
thing I should mention though is you can
ever say an object has order of rotation
once so if we had an object that didn't
have rotational symmetry so let me just
bring up a random object here cut this
out and like page this object right here
if we rotate this thing it's never going
to coincide with itself except when we
get back to a full 360 degree rotation
this object does not have an order of
rotation on one it has an order it
doesn't have an order of rotation we
simply say that it's not has no
rotational symmetry okay so keep that
that's a common mistake that sometimes
people make but yeah rotational symmetry
called size itself in rotational
blessing series all right thanks guys
soaps