Presentation on theme: "Chapter 4, Unit 1 Maths – 8th Grade"— Presentation transcript:
1Chapter 4, Unit 1 Maths – 8th Grade MensurationChapter 4, Unit 1Maths – 8th Grade
2Introduction What are Solid Objects? Look at objects around you. Table, chair, classroom. They have the following properties:Occupy fixed amount of space.Have fixed size and shape.Can contain other items.Eg: pencil box contains pencils,rubbers.Eg: classroom contains tables, chairs, students.All these objects are called three dimentional (3D) objects
3Introduction What are the shapes of these solid objects? Many shapes exist:CuboidCubeCylinderConeSphereTriangular Prism
4Identify shapes around you Look around you. You will find solid objects with different shapes. Identify these solid shapes:
5Cuboid A cuboid is a box-shaped solid object. It has six flat sides and all angles are right angles.And all of its faces are rectangles.It has three important measures:Height (h)Length (l)Breadth (b)
6Cube A box-shaped solid object. It has six identical square faces. A cuboid whose length, breadth and height are all equal is called a cube. (h = l = b)
10Différence Between LSA and TSA Lateral surface area(LSA) in a solid is the sum of the surface areas of all its faces excluding the base and top of the solid.(e.g. Area required for painting a room(cuboid))TSATotal surface area (TSA) in a solid is the sum of the surface areas of all its faces including the base and top of the solid.(e.g. Area required for covering/wrapping a cuboid)
11TSA and LSA of Cuboid (lh+bh+lh+bh) 2(lh+bh) 1. Consider the Cuboid ABCDEFGH2. Open the cuboid along DH3. For LSA we need not to consider area of II and VI4. Lateral Surface Area(lh+bh+lh+bh)5. Lateral Surface Area2(lh+bh)
12TSA and LSA of Cuboid Total Surface Area (lh+bh+lh+bh+lb+lb) .Total Surface Area(lh+bh+lh+bh+lb+lb)7. Total Surface Area2(lh+bh+lb)References :
13TSA and LSA of Cube l = b = h 1. A cube is a simple cuboid where 2. LSA for the cube = 2(a*a + a*a) = 4a23. TSA for the cube = 2(a*a + a*a + a*a) = 6a2
14Excercies1. How many tiles each of 30cm*20cm is required to to cover a hall of dimensions 15m*12m.Ans. 3000(How)Here hall dimensions are given in meters so dimensions are 1500cm*1200cmSo hall area=1500*1200cm2Area of a single tile=30*20cm2So number of tiles=(1500*1200)/(30*20)=3000
15Excercies2. Find the length of each side of a cube having the total surface area as 294cm2.Ans. 7 cm. (How)Here surface area is 294cm2.So TSA of a cube is 6a2So a2=294/6=49cm2a=7cm
16VolumeAmount of space occupied by a three dimentional solid object is called its volume.It can be thought of as capacity of a solid object.Interesting story:At a conference in USA, all scientists and mathematicians were present. One guy took up a hollow container of distorted (arbitrary) shape and asked what would its volume be?All the mathematicians started applying formulae but couldn’t get the right answere because the shape of the container was not proper.At the time, a small boy came, took the container, filled it with water. Then, he poured the water in a measuring cylinder and got the exact volume of the container!Everybody started clapping seeing the young boy’s presence of mind!
17Volume of a cube Suppose we have 100 cubes of side length 1 cm. each. Q. How many such cubes should we use to make a bigger cube of side length 2 cm.?Take a cube of 1 cm.Dimentions are 1x1x1Increase its height to 2 cm. by putting another such cube below it.Dimentions are 2x1x1.. Not a cube!!Now increase its length to 2 cm. by putting 2 such cubes next to it.Dimentions are 2x2x1.. Not a cube!!Now increase its breadth to 2 cm. By putting 4 such cubes next to it.Dimentions are 2x2x2.. Now it becomes a cube!
18Volume of a cubeSo, we need 8 cubes to make a cube of side length 2 cm.i.e its volume is 8 cubic unitsVolume of cube = side x side x side = (side)3Eg: for cube of side 2 cm. volume = 2 cm x 2 cm x 2 cm = 8 cm3Check “Try it yourself section” on this link. (link)
19Volume of a cuboid Suppose we have 24 cubes of side length 1 cm. each. Q. Arrange them to form a cuboids of different dimentions.Observe the following table :We can see that using 24 cubes, we can arrange them in:
20Volume of a cuboidSo, we see all the 3 cuboids in prev. slide have the same volume i.e 24 cubic units.Volume of a cuboid = length x breadth x heightVolume of a cuboid = base area x height (area = length x breadth)Eg: Volume of cuboid of dimentions 2 cm. x 3 cm. x 4 cm. = 24 cm3Eg: Volume of cuboid of dimentions 3 m. x 5 m. x 10 m. = 150 m3
21Excercies2. A match box measure 4cm*2.5cm*1.5cm.What will be the volume of packet containg 12 such boxes.Ans. 180 cm3. (How)Here matchbox measure is 4cm*2.5cm*1.5cm.So Volume of a match box is 4*2.5*1.5=15cm3So Volume of a packet conating 12 boxes is 15*12=180cm3
22Excercies2. A match box measure 4cm*2.5cm*1.5cm.What will be the volume of packet containg 12 such boxes.Ans. 180 cm3. (How)Here matchbox measure is 4cm*2.5cm*1.5cm.So Volume of a match box is 4*2.5*1.5=15cm3So Volume of a packet conating 12 boxes is 15*12=180cm3
23Summary Topic Formula LSA of a cuboid 2(lh+bh) TSA of a cuboid 2(lh+bh+lb)Volume of cuboidl*b*h (base area*height)LSA of a cube4a2TSA of a cube6a2Volume of a cubea3For cuboid, l=length, b=breadth, h=heightFor cube, a=side of cubeArea is measured in square units whereas volume is measured in cubic units.