Suppose you are redecorating your room and need to know the amount of floor space available. So, you measure the floor which is, in fact, finding the area of that room. Now, suppose you plan to fill up your pool with water. You measure how much water is needed to fill the pool by measuring its volume.
In geometry, it is important to know the space covered by certain 2-dimensional and 3-dimensional figures. We can determine this space by calculating area and volume based on the type of figure. Here we will understand the basic concept of area and volume as related to various types of figures.
Meaning of area in geometry
The total space occupied by the two-dimensional surface of an object or a flat shape is called an area.
Many different area formulas are available to determine the area of various two-dimensional shapes. We can also determine a shape's area by counting the number of unit squares that cover the entire surface of the object. This method helps us to learn and understand the concept of area. See the image below which displays the concept of the square unit. You will find that area formulas are easier and faster to use, however. The unit of area is always measured in square units like square centimeters, square meters, square inches, and so on.
Area of 2D figure, splashlearn.com
Here are some facts about area to keep in mind:
- The area and perimeter of shapes are different calculations and can often be confused with one another.
- The area of any figure is mostly calculated based on the terms like side, length, base, height, and radius.
- The area of two congruent (identical) figures will be the same, but sometimes two non-congruent (not identical) figures might have the same area.
Area formulas for plain figures (2D)
Let's take a look at some of the different formulas for area of basic and common geometric figures, including:
- Area of rectangle
- Area of square
- Area of triangle
- Area of circle
- Area of parallelogram
Area of rectangle
We can calculate the area of a rectangle with width w and height h as follows:
Area of Rectangle
Area of rectangle - StudySmarter Originals
Area of square
Squares have four sides which are all equal in length. So, we can calculate the area with the given formula:
Area of Square
where a is the length of side
Area of square - StudySmarter Originals
Area of triangle
We can calculate the area of the triangle with the help of its altitude h and its base b.
Area of Triangle
Area of Triangle - StudySmarter Originals
Area of circle
The space occupied by the circle can be calculated based on its radius.
Area of circle
where r is the radius of the circle
Area of circle - StudySmarter Originals
Area of parallelogram
A parallelogram is a figure with opposite sides as a pair of parallel lines.
Area of parallelogram
where b is the base and h is the height of the parallelogram
Area of parallelogram - StudySmarter Originals
Meaning of surface area in geometry
The term surface area is associated with three-dimensional figures and objects. However, its concept is essentially the same as area in that it measures the size of the surface using square units like inches squared (in2). Formulas for surface areas differ based on the type of 3-dimensional object.
The total area occupied by the outer surfaces of any 3-dimensional object is called the surface area of that object.
Surface Area - StudySmarter Originals
In other words, the area occupied by all the faces and sides of any 3D object is its surface area. For any figure, surface area can be classified into three types:
- Lateral surface area
- Curved surface area
- Total surface area
Types of surface area
The three types of surface area (lateral, curved, and total) are explained here.
Lateral and curved surface area
The surface area of the entire 3D shape excluding the surface area of the base and top is known as the lateral surface area.
The surface area of all curved surfaces of the 3D shape is known as the curved surface area.
Sometimes, the lateral surface area and the curved surface area are actually referring to the same part of the 3D shape. This is the case for shapes with curved surfaces like cylinders and cones, for example. Shapes like cubes, however, do not have curved surface area, and this term does not apply.
Lateral surface area - StudySmarter Originals
Here in the figure of the cylinder, the gray surface is the lateral surface, which is the surface that surrounds the cylinder. When calculating the lateral surface area, we will consider the gray color surface shown but not the white top surface or white bottom surface of the cylinder.
Total surface area
The total area of all surfaces and sides of an object is called the total surface area.
In other words, we include any and all surfaces of an object when calculating the total surface area, as opposed to the lateral surface area. Usually, we simply refer to the total surface area as surface area.
Total surface area - StudySmarter Originals
Here, we consider the surface area of both the lateral surface (light gray color) and top & base (dark gray color) when we calculate the total surface area of this cylinder.
Surface area formulas
Let's take a look at some of the surface area formulas for common three-dimensional figures.
Surface area of cube
A cube is a three-dimensional figure consisting of six square faces. The surface area of a cube can be obtained by finding the area of all six faces and summing them up together. For the lateral surface area of the cube, we take only four faces into consideration, eliminating the top and bottom sides.
Surface area of cube - StudySmarter Originals
The formula for the surface area of a cube is as follows:
Total surface area of cube
Lateral surface area of cube
where a is the length of all sides
Surface area of cuboid
A cuboid is a three-dimensional figure with all six faces rectangular. The total surface area and lateral surface of the cuboid can be calculated in the same manner as a cube. However, for a cuboid, instead of using the same measurement for all six faces, we consider and measure the different faces separately. Hence, we calculate the surface area of the cuboid in terms of length l, width w, and height h.
Surface area of cuboid - StudySmarter Originals
The formula for the surface area of a cuboid is as follows:
Total surface area of cuboid
Lateral surface area of cuboid
Surface area of cylinder
A cylinder is a 3D shape with two flat circular faces, one on the top and one on the bottom, attached at the opposite ends of a curved face. A simple example is a pipe with both of the ends sealed or closed. The surface area of a cylinder is the sum of the surface areas of both circular bases and the curved surface area. When determining only the lateral or curved surface area, just the curved surface of the cylinder is considered.
Surface area of cylinder - StudySmarter Originals
The formula for the surface area of a cylinder is as follows:
Total surface area of cylinder
Lateral surface area of cylinder
where r is the radius of circular base and h is the height of a cylinder
Surface area of sphere
A sphere is the three-dimensional representation of a circle. As spheres have only one overall surface and no other faces, discussing its lateral surface area doesn't make sense, as it would be the same as its total surface area. Therefore, we only calculate the total surface area for spheres.
Surface area of sphere - StudySmarter Originals
The formula for the surface area of a cuboid is as follows:
Total surface area of sphere
where r is the radius of the sphere
Meaning of volume in geometry
Any three-dimensional object in nature occupies space. So, the space occupied by that object is called its volume.
The space enclosed within the object or the space occupied by any three-dimensional solid object is known as volume.
To measure the volume we divide the occupied space into equal cubical units and calculate the total occupied cubical units, The unit of volume can be in a cubic centimeter, cubic meter, cubic inches, and so on.
Volume of 3D object visualization, tasks.illustrativemathematics.org
Volume formulas
Let's understand some of the formulas of volume for familiar 3D objects and shapes.
Volume of cube
As all the sides in the cube are of equal length, we can calculate the volume of a cube using the formula given below:
Volume of cube
where a is the length of sides for all faces
Volume of cube - StudySmarter Originals
Volume of cuboid
Unlike a cube, a cuboid has sides of different measures. So, we calculate the volume in the terms of length l, width w, and height h. The volume formula for a cuboid is as follows:
Volume of cuboid
Volume of cuboid - StudySmarter Originals
Volume of cylinder
As the cylinder is formed from its circular bases and the distance between them, we consider the radius r of the circular base and height h of the cylinder when calculating its volume. The formula is as follows:
Volume of cylinder
Volume of Cylinder - StudySmarter Originals
Volume of sphere
As it can be used in some applications to approximate the shape of Earth, we have a special interest in the sphere, the three-dimensional representation of a circle. The volume of a sphere can be derived using multiple methods, including the Archimedes formula and Cavalieri's principle, for example. For now, we will just take a brief glance at its commonly accepted volume formula:
Volume of sphere
where r is the radius of the sphere
Volume of sphere - StudySmarter Originals
Area and volume - Key takeaways
- The total space occupied by the 2-dimensional surface of an object or a flat shape is called area. Area uses square units, like feet squared or meters squared.
- The area of two congruent (identical) figures will be the same, but sometimes two non-congruent figures might have the same area.
- The total area occupied by the outer surfaces of any 3-dimensional object is called the surface area of that object. Surface area uses square units.
- Surface can be classified into three types: lateral surface area, curved surface area, and total surface area.
- The space enclosed within the object or the space occupied by any three-dimensional solid object is known as volume.
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