About this video
Arianna turns a stove dial 135 degrees to the right, and we find the setting without a protractor. A 90-degree turn from the top lands on low, and a 180-degree turn lands on medium. Since 135 is halfway between 90 and 180, the dial lands on medium-low.
You'll be able to
- use benchmark angles of 90 and 180 degrees to estimate other angles.
- picture a turn of a given number of degrees starting from the top, like on a clock.
- solve a word problem about turning a dial by a number of degrees.
Key words
- 90-degree angle
- A square corner, a quarter turn; also called a right angle.
- straight angle
- A 180-degree angle, a half turn, where the two sides make a straight line.
- protractor
- A tool for measuring angles in degrees.
Transcript
- [Voiceover] If Arianna turns the stove dial 135 degrees to the right, what setting will the dial be on? So two very important things up here. First she's turning the dial 135 degrees. And which way is she turning the dial? She's turning the dial to the right.
So here's our dial it's facing up. This red dial right here. Facing up sort of like on a clock. And we're going to be turning the dial to the right. And how far to the right? 135 degrees. So this dial will turn until it's reached 135 degrees. So how can we figure out if we start turning this dial when to stop?
When it's reached 135 degrees. Well, one common way would be to use a protractor. We could set up our protractor, measure out 135 degrees. But in this case we can't do that 'cause we don't have a protractor. So let's use some other information. Some other stuff we know about angles to see if we can solve this.
One thing I know, one angle that we see a lot is a 90 degree angle. And a 90 degree angle if we start up at the top like our dial and turn 90 degrees, we're gonna end up with an angle like this. An angle where we could put a square in the middle and finish the square.
Well it's like a square angle. So this is a 90 degree angle. So coming over to our dial, if we start at the top and we go 90 degrees. So we start here at the top and we go 90 degrees, we'd end up on the low setting. 90 degrees. But we're not going 90 we're going 135 which is more than 90 degrees.
So here's one clue. We know we're going farther than the low setting. We don't know how much farther. We're definitely gonna go past the low setting. Another angle I could use to help me is the straight angle. 180 degrees. If 180 degree angle again starts at the top like our knob is currently.
Like our dial. It will go all the way around until we have a straight angle like this. So again, looking at our knob, if we started at the top and we went around 180 degrees, we would end up facing straight down at medium. This would be 180 degrees. So where does 135 fall?
Well 135 falls somewhere in between 90 and 180. 90 was not far enough of a turn. And 180 was too far of a turn. So we want something in the middle. And what setting is in the middle of the 90 and the 180? Right here in the middle of them is medium-low. So turning our stove to 135 degrees to the right will set our stove to medium-low.
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