this video looks at the area the perimeter and the volume of some circular shapes some of the basic terms we're going to be using are as follows the first we'll be looking at is the radius the radius is the distance from the center of the circle to the outside of the circle okay and it doesn't matter where you we talk about on the outside of the circle the distance from distance from the middle to the outside is always the same the next one we're going to be looking at is a diameter a diameter describes the distance across the span of the circle and what you probably realize is this is the twice the distance of the radius the next one I'll be using is a circumference the circumference is the same as saying the perimeter of a circle and it's a distance around the outside of the circle final thing we're going to be using is this Greek letter Pi Pi = 3.14 okay and the symbol is is showing and this constant number 3.14 you'll be using a fair bit when you're working with circles so first off we'll have a look at the area Okay so the area of a circle is PK r s which means < * R * R so we'll consider where we have a radius of 5 cm substituting the value in area = < * 5 2 which = 3.14 * 5 * 5 which multiplying those out gives gives us an answer of roughly 78 CM squ okay let's have a look at another example in this example we have a radius of 11 M so we'll substitute in the values so the area = piun * 11 * 11 this equals 3.14 * 11 * 11 which equal 38013 m² okay so when working at it's just a simple matter of substituting the radius into that formula PK r² next we'll have a look at the circumference so as you remember the circumference is the same the saying the perimeter of the circle it's the distance around the outside the circumference = 2 R once again it's just a matter of substituting in the value so so the radius is 9 cm the circumference would equal 2 * < * 9 which = 2 * 3. 4 * 9 which when you calculate it is 5655 CM have a look at another example so in the next example we have a diameter which is 9 cm okay so we have to work out what the radius is the radius is going to be half the diameter so half of 9 is 4.5 cm and we just substitute this into the formula circumference is 2 * piun 4.5 which is 2 * 3.14 by 4.5 which gives us an answer of 28.2 cm and that's a circumference next thing we'll look at is working at the volume of a cylinder we considering the volume of a cylinder rather than give you a big fancy formula first off I'm going to just get you to consider the different parts now the area of the circle part of a cylinder we've already seen as PK r s the other thing we deal with is the height so how do we use these two to work out the volume from the cylinder well the volume put quite simply is the area of the circle times the height so you could work that out in Formula very easily so the area is PK R 2 so the volume is PK r s * the height so let's use this to work at the volume of a few different cylinders first off let's work work on where we've got a radius in the cylinder of 4 cm and a height of 11 cm so what we'll do is I'll shade in the circle part and leave the other height part blank just so you can separate the two for stars so < r^ 2 is 3.14x 4X 4 the height still time 11 soal .27 * 11 so you times all this together and you get 55292420 12 M and a height of 7 m m so the radius is going to be half of the diameter which is 6 M we'll substitute this Ink r^ 2 is 3.14x 6X 6 * 17 working this out this equals 1310 * 17 so the volume of the cylinder is 1922. 65 M cubed so anyway to sum it all up first off the area of a circle is PK R 2 where piun is 3.14 R is the radius circumference of a circle the perimeter is 2 piun R the volume of a cylinder is basically the area piun R 2 * the height so if you can work that out you should do well with circular shapes okay good luck with that bye