• 2 months ago
Transcript
00:00Hey guys, I am trying to take care of my corn, but as you can see, some of these guys are
00:06intent on eating it before I harvest. I need to put a fence around the perimeter of the
00:11field so they don't eat all of it. We need to learn about perimeter so that I know how
00:16many fence pieces to buy for the cornfield. Let's go learn about perimeter and then get
00:21back to the cornfield, or what is left after these guys are done.
00:27Perimeter is a math term that means the distance around a shape. If we want to build a fence
00:31around the perimeter of the field, then we need to know how to find the perimeter. Knowing
00:36the perimeter will let us know how many fence pieces we need.
00:41Today we are only going to talk about perimeter with polygons. Do you remember what a polygon
00:46is? A polygon is a closed shape with straight sides like this square. The perimeter of the
00:53square is the shortest distance around it. So if we wanted to put a fence just around
00:57the square we would want to measure this part, and not something like this. This squiggly
01:05line is not the shortest distance around the square. The border around the square shows
01:09the shortest distance, which is the perimeter. Here is a rectangle. We can see someone measured
01:16the sides for us. Perimeter is something we can measure in units like centimeters or inches
01:21or even miles. If the problem we are given has units listed, we need to remember to keep
01:27that unit in the answer. To find the perimeter of a polygon, you just
01:32add up all the sides together. You can add the sides in any order, but I like putting
01:38the same numbers together to make it easier. What is 10 plus 10 plus 5 plus 5?
01:46The answer is 30, but wait, we are missing something. The perimeter is 30 centimeters.
01:53Don't forget that if they give you a unit of measurement, you need to keep it in the
01:56answer. Great job! Something that confused me for a little while
02:01was the difference between perimeter and area, so let's talk about it.
02:06Perimeter is the length around the object, and area is everything inside the shape. You
02:11do not want to confuse perimeter and area. The perimeter is 30 in this problem. To find
02:17the area of a square or rectangle, you might remember you multiply the length times the
02:22width. 5 times 10 is 50 centimeters squared. As you can see, area is not the same as perimeter,
02:31so don't confuse the two. Even if the numbers in some problems equal each other, they mean
02:36something different. Here we have a square, but we only know one
02:42side, so how are we supposed to figure out the perimeter? The way to figure out many
02:46of these problems is to use what we know about shapes. A square is awesome because all sides
02:53are equal. So if we know one side is 5 inches, that means all the sides measure 5 inches.
03:01To find the perimeter, we add all the sides together. What is the perimeter? 20 inches
03:09is the perimeter. Great job! Because all sides are equal, we could have
03:13used multiplication to find the answer as well. For example, we could have multiplied
03:18the amount of sides, 4 times the measurement of one side, which is 5 inches. 4 times 5
03:25equals 20. 20 inches, just like adding them all up. Awesome!
03:31Multiplication is repeated addition, but when finding perimeter, you can only use multiplication
03:35when the polygon's sides are all the same length. So if all sides are the same length,
03:41you can multiply that length by the number of sides to get your perimeter. This can be
03:46tricky to remember, so if you have any doubt, add up all the sides and you know you will
03:50get your perimeter. We need to find the perimeter of this rectangle.
03:56We know the top side is 6 centimeters and the right side is 4 centimeters. How can we
04:01find the length of the other sides? Just like before, using our knowledge of shapes
04:06will help. In a rectangle, the sides opposite each other are the same length. So the 6 centimeter
04:12side is the same length as the bottom side. The right side is 4 centimeters, which means
04:19the left side will also be 4 centimeters. We now have all our side lengths.
04:26What is the perimeter of this rectangle? The answer is 20 centimeters. Great job! Let's
04:34take a look at how many fence pieces I will need for my cornfield.
04:39This is the shape of my cornfield and it is divided into different squares. I need to
04:43know the perimeter of the entire cornfield. As you can see, it is not a perfect rectangle
04:49and I don't have measurements in feet, but I do know that each of these segments are
04:54the same size as one of the fence pieces. So how do you think we can figure out how
04:59many fence pieces we will need? What we can do is just count the outside segments. Starting
05:06in the top left corner, we count 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14.
05:19We need a total of 14 fence pieces in all. Great job guys! We learned how to find perimeter.
05:26We also learned that knowing shapes helps us solve problems with perimeter.
05:31I did not get the right height of fence, did I? Come on guys, at least wait until harvest
05:39time to eat it all.