Volume and Surface Area of Three-dimensional Figures
The most common three-dimensional figures are: prisms, cylinders, pyramids, cones and spheres. They all have two important qualities: volume and surface area. Here is a list containing the figures and their properties.
Example 1
A prism has a triangle with the area as its base, and height . Calculate the volume of the prism.
You’ll find the volume by multiplying the area of the base with the height :
Example 2
A cylinder has the radius and height . Calculate the volume and the surface area of the cylinder.
The formula for the volume of a cylinder is . You have the height , but have to find the base area . Since the base area in a cylinder is a circle, you’ll have to find the area of a circle:
Now you’ll find the volume of a cylinder by multiplying the base area with the height :
To find the surface area of a cylinder, you add together the areas of all the sides. The green rectangle you see on the drawing comes from cutting and folding out the walls of the cylinder. First, you calculate the area of the top and bottom of the cylinder (they have the same area), and then the area of the rectangle which is the height. The length of the rectangle is the circumference of the circle (see the figure):
The surface area of a cylinder then becomes
Example 3
A pyramid has a triangle with area as its base. The height of the pyramid is . Calculate the volume of the pyramid.
You’ll find the volume of the pyramid by multiplying the area of the base area with the height , and the dividing by 3:
Example 4
A cone has a circle with radius as its base. The height of the cone is and side . Calculate the volume and the surface area of the cone.
The volume has the formula , so you first need to find the area of the base . The area of the circle is:
Then you’ll find the volume of the cone by multiplying the area of the base with the height , and then divide by 3:
You’ll find the surface area by using the formula for the surface area of a cone. Here you can put your values directly in to the formula and calculate.
Example 5
A sphere has radius . Calculate the volume and the surface area of the sphere.
You1’ll find the volume by using the formula for the volume of a sphere:
You’ll find the surface area by using the formula for the surface area of a sphere: