Measuring angles - Degrees and Protractors - Free Educational videos for Students in K-12

Measuring angles - Degrees and Protractors - By tecmath

Transcript


00:01	Welcome to take Math Channel . What we're going to
00:02	be having a look at in this video is how
00:04	to measure angles and not only that , we're going
00:07	to look at a few other things . Actually we're
00:09	going to look at first off just the way that
00:10	we measure angles and we're gonna have a look at
00:12	some different types of angles and their measurements . They
00:14	have some common angles were also then look at how
00:17	to construct angles . Okay , so hope you enjoy
00:20	this video . Hope it comes in handy for you
00:22	. So the first off thing I'll do is I'm
00:25	just going to have a quick recap on what an
00:26	angle is made a previous video an angle . So
00:29	it might be worth watching . But if you can't
00:31	be bothered , you just want to get straight into
00:32	it . The first thing is where two lines meet
00:35	. So so we have two lines meeting here .
00:38	What we have is first off , we have two
00:41	arms meeting here . The spot where they meet ,
00:45	it's called the vertex . Some of you guys might
00:47	be thinking , hey in the previous video this is
00:49	called an intersection where lines cross is called an intersection
00:52	. It was just a point like this is called
00:53	a vertex . But this little gap that we have
00:56	here , this little space between the two arms .
00:58	This is called an angle and we're going to look
01:02	at how we go about measuring these because it's fairly
01:05	simple . So first off the way that we measure
01:09	an angle or any angle is using one of these
01:12	guys , which is a protractor . Now protractor ,
01:14	you might actually have a different version of one of
01:16	these whether they're full circle . They either come in
01:18	half circles or full circles but for either one of
01:23	them they're divided up into these little party . You'll
01:25	see , okay , are these little units here 10
01:28	2030 40 ? But even these smaller units here .
01:31	Okay . All up This divide up to 360 little
01:36	parts , and each one of these little part is
01:38	called a Degree . So 360°. . The simple we
01:44	use for these is degrees like this . So it's
01:46	kind of like degrees that you might have heard of
01:48	when you are think of temperature . Okay , so
01:50	it is a similar sort of word that uses a
01:53	similar sort of symbol , but once measuring temperature and
01:57	one is measuring the size of an angle . So
02:00	how do we use one of these betraying uh tractors
02:02	? Well , what I'll do is first off ,
02:04	I'll show you uh just some common angles that you'll
02:07	get with them . Okay , so first off ,
02:10	imagine that we had Mhm . Two arms and their
02:14	meeting at the same point . Now , this is
02:16	going to be the first angle we're looking at .
02:18	So one arm is pointing this way and the other
02:20	arm is also pointing in exactly the same direction You
02:24	might behave . You measure this , you're getting 0°
02:28	and you'd be exactly right . This is just a
02:31	I guess it's no angle 0°, , but it's a
02:33	great little base to start from . Okay , so
02:37	We're gonna start with this idea of 0° , and
02:40	we're just going to make our angles progressively bigger .
02:43	Okay , So so say we had one of our
02:46	arms going off to zero degrees here , and now
02:49	we had , as you might remember from the previous
02:51	video going up through this particular party . So we
02:54	form what is known as a right angle . All
02:57	right , That appears a right angle . Again ,
03:01	a previous video we looked at these . They are
03:03	symbolized by this . You'll notice that these guys go
03:06	up through the 90°. . This is a really ,
03:09	really important angle to remember . This is the reason
03:13	is because this is the angle which occurs on the
03:16	corners of say squares and rectangles and things like this
03:19	. So an angle which goes up like this ,
03:22	which where the lines are coming one perpendicular from the
03:25	other is a right angle . Okay , so I'll
03:30	get rid of that and I'll now talk about angles
03:33	which occur between 0° and right angles . You might
03:36	remember these were called acute angles and these were any
03:41	angle which occurred between 90 degrees and 0°. . So
03:48	I'll give you an example of this , I'll get
03:49	rid of , I'll just put this uh up here
03:52	on 90 . So we can remember that's a right
03:53	angle . But say we had an angle going up
03:57	this way . Okay , just selecting the right pen
04:00	there and say I had an angle which is going
04:02	up . Yeah , You might look at this and
04:05	say , Hey , this is going up about 61
04:09	, And this is an example of an acute angle
04:11	. It's an angle which is between zero and 90°.
04:16	. Okay , so An acute angle , I'll just
04:18	put that in there . It's between zero at 30
04:22	degrees . Okay ? So say we made our arms
04:26	go further and further and further apart now and eventually
04:30	they went all the way around . So we follow
04:32	this baseline right along on a tractor . You're going
04:36	to see that we go all the way around to
04:38	this measurement here , Which is 180° 180° by the
04:43	way . This an angle like this , you might
04:45	remember from the early video I made is called a
04:48	straight angle . You probably get the idea of why
04:50	that's called a straight angle B that it forms a
04:53	straight line . Okay , So straight angle is 180°.
04:58	. Another really important one to remember . Okay ,
05:02	so so far we've got zero degrees . A right
05:06	angle is 90 degrees . A straight angle is 180
05:08	degrees . And any angles between zero and 90 which
05:11	are called acute angles . There's another group of angles
05:15	which are any angles between our right angle and are
05:19	straight angle between this 90 and 1 80 between 90
05:23	degrees and 1 80 degrees . And you might remember
05:27	These were called up to singles . Okay , so
05:31	obtuse angles angles which occur between 90 and 180°. .
05:37	So we could keep going all the way around because
05:39	we're not completely finished yet . We can keep going
05:42	around in this circle because our angle could extend even
05:46	beyond this . And so so as to get rid
05:48	of this line . I'll put this 180 here so
05:50	we remember that's there . But I can keep going
05:53	here and I'm just going to zoom out a little
05:55	bit so we can see this . So say I
05:58	keep going and I start to measure say an angle
06:03	which occurs this big . Okay , so what I'm
06:07	talking about here is an angle , say this big
06:10	. If this is the case , we're going beyond
06:14	just our any of these angles and we hit this
06:18	zone in here , which anywhere within this zone ,
06:22	anywhere right around all the way back 2 360° ,
06:29	Which is called a reflex . So any angle which
06:32	is 100 80 degrees , 2 360° is called a
06:40	reflex angle . Okay , just one little thing with
06:44	this , you might also realize that you could come
06:46	down 270°. . Another important one to remember , and
06:50	although the angle we're talking about is going around here
06:53	, we do form a little 90° on the outer
06:56	part of our angle there . So it's another good
06:58	one to remember there . So say You might actually
07:03	consider say why do we bother have 360° when we
07:06	Go all the way around 0°? ? The same as
07:09	360°. . The answer to that is No . Okay
07:14	, 0° is where we have no angle 360° is
07:19	where what we do is our angle two arms meet
07:25	, but we're actually talking about Okay , so our
07:26	two arms going this way , but our angle we're
07:29	talking about is this party of the complete rotation .
07:32	Okay . Rather than this . Nothing space in between
07:35	. Okay , so there are different types of angles
07:38	on a circle . Okay . Uh really , really
07:41	important to remember , especially the right angle here and
07:44	the straight angle here , I think , and that
07:46	, knowing there's 360° in a circle , I think
07:49	they're probably the most important things . So how do
07:53	we go about measuring the angles in a circle ?
07:56	Okay . That's the uh the next part of what
07:58	we look at . You probably got this idea already
08:01	. We're gonna well what you do is you get
08:04	your angle , I'm actually just gonna superimpose an angle
08:07	on top of all going back in there and I'm
08:09	gonna superimpose an angle on top of what we're doing
08:12	because ah look , the program you'll have doesn't actually
08:16	work very well to actually move my tractor around .
08:19	So so here I'm going to draw this angle a
08:22	little bit , I'm gonna draw an easy one to
08:24	start off with and get you to try and name
08:25	what it is to say this was my angle .
08:30	You're going to notice . First off , what you
08:31	do is you put the vertex of your angle on
08:36	this center point here and you have the horizontal coming
08:39	off on a zero . So one of the baselines
08:42	of your angle coming off at a zero , but
08:44	say I have an angle here , which is just
08:49	there , what is it ? So you might go
08:50	around and go , okay , it's 10 2030 40
08:53	50 60 70 80 degrees . And you might be
08:55	able to even go that next step and say that's
08:57	an acute angle and you'd be right . It is
08:59	a fairly cute little angle . Okay , a terrible
09:03	math joke , Okay . Um and you'd be right
09:05	, but just what you're doing this , you have
09:06	to make sure that you're lining up your vertex with
09:10	your center point here , of your protractor . And
09:12	also the baseline here lines up now , I just
09:15	want to show you one other little pitfall that you
09:17	can get in when you're measuring angles , which is
09:19	this one ? Say I'm measuring this particular angle here
09:23	. Okay , I've got my verse vertex here .
09:27	Everything is good in the world . I measured it
09:28	up , I've kept it on zero because there's a
09:30	little zero down there and I'm going to measure this
09:34	. I go , Mhm . You might say ,
09:37	okay , what angle are we talking about here ?
09:41	So you might look at this automatically say , Hey
09:43	, that's 130°. . I hate to break it to
09:46	you . You're not correct . Uh Because what we
09:49	have here is we're only talking about this particular little
09:52	angle here . So you're gonna look at this and
09:53	say , hey , wait a second . This angle
09:55	is less than nine degrees . It's acute angle .
09:57	So it's a really , really important thing . Before
10:00	you measure any angle I think is to actually try
10:02	to make a bit of a guess about how big
10:04	it is . Okay . And if you're having a
10:06	look at this , you might actually notice that this
10:08	we're going up 10 20 30 40 50 degrees .
10:13	Okay , So start from the zero , which is
10:15	where you can't see it . I've crossed it out
10:16	being a mean spirited person . I am , but
10:18	this is only a 50 degree angle . Make sure
10:22	you're reading the right one . Okay . We're not
10:24	reading this part out here . We're reading this particular
10:26	section here . Okay . All right . Uh just
10:32	last thing , you probably get the idea of how
10:35	to construct an angle . So say we wanted to
10:36	construct an angle that was Uh what about we want
10:41	to construct an angle that is 130° big . So
10:46	usually what I do with this is you're not going
10:49	to be able to necessarily drawn up a tractor like
10:51	I can , but what I do is I would
10:54	start with my advertises and I would draw the baseline
10:58	, okay , just one baseline going that way ,
11:01	but I'd probably do a better job of it than
11:03	my messy thing there and then what you can do
11:05	is you can move this protractor , so what we
11:08	do is we're going to move this protractor , if
11:11	this protractor wants to move , I'm going to have
11:13	this real problem with the tractor , won't want to
11:15	move . So we actually look , it's definitely not
11:20	going to move that , you knew that was going
11:21	to happen , didn't you pretend we can move it
11:24	? So what we're gonna eventually do , we'll move
11:26	it . So for the cheetah year is there ?
11:29	So we'd move it . So these guys live it
11:32	up okay on the zero and say what ? We're
11:35	trying to draw 100 and 30 degrees . I'd now
11:38	mark this area in , I'd get rid of my
11:41	protractor so pretend we got rid of that tractor altogether
11:44	. And now I would draw this line here .
11:48	The next thing I do is I make sure I
11:51	labeled by Angle . Okay . Even if I market
11:55	like this , I might never go that next step
11:57	of writing 130°. . Okay . So anyway , I
12:03	hope you found that video informative . Um , we
12:07	are going to do some more video angles . Are
12:08	videos . So hopefully you have a look at those
12:11	. This is just a nice basic thing to start
12:13	off with practice drawing angles . They're really , really
12:15	handy little things . Anyway , see you next time
12:18	. Bye .

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