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| 19 Theory slides |
| 13 Exercises - Grade E - A |
| Each lesson is meant to take 1-2 classroom sessions |
Here are a few recommended readings before getting started with this lesson.
Prisms can be categorized by the shape of their bases. For example, a prism with a triangular base is called a triangular prism. A rectangular prism, on the other hand, has a rectangular base.
Determine whether the given solid is a triangular prism, a rectangular prism, or neither.
There are two important characteristics that give information about 3D objects.
The volume of a solid is the measure of the amount of space inside the solid. It is the three-dimensional equivalent of the area of the figure. Volume is measured using cubic units, such as cubic meters, or m3. The applet below illustrates the volume of some solids. Move the slider to fill the solids.
The surface area SA of a three-dimensional shape is the total area of all the surfaces of the shape. The lateral area LA is the total area of all lateral surfaces, the surfaces of the shape that are not bases. Lateral area can be defined for polyhedrons, cones, and cylinders. In these instances, the surface area of the shape can be calculated by the formula below.
The net of a solid can be helpful to visualize the surfaces of a three-dimensional figure.
Consider a prism with a base area B and height h.
The volume of the prism is calculated by multiplying the base's area by its height.
V=Bh
By Cavalieri's principle, this formula holds true for all types of prisms, including skewed ones.
Recall that the volume of a solid is the measure of the amount of space inside the solid. Note that the top and bottom faces of the prism are always the same and parallel to each other.
Additionally, the prism is, so to speak, filled
with identical base areas that are stacked on top of each other to the height of the prism.
Consider a prism with a height h, base area B, and base perimeter P.
The surface area of the prism is the sum of the two base areas and the lateral area, which can be calculated as the product of the base perimeter and the height of the prism.
SA=2B+Ph
Note that although this proof is written for a regular prism, it is also true for a non-regular prism.
It is possible to derive two specific formulas for the volume and surface area of a rectangular prism.
Consider a rectangular prism with a width w, length ℓ, and height h.
The volume of the prism is calculated by multiplying the area of the base by the height of the prism.
V=wℓh
Consider a rectangular prism with a height h, base area B, and base perimeter P.
The surface area of the rectangular prism can be found using the following formula.
SA=2(wℓ+hℓ+hw)
P=2(w+ℓ), B=wℓ
Distribute h
Factor out 2
Consider a cube with a side length s.
The volume V of the cube can be calculated by raising the side length s to the power of 3, or cubing
it.
V=s3
Consider a cube with a side length s.
The surface area of the cube is given by the following formula.
SA=6s2
Substitute values
a⋅a=a2
Add terms
Substitute values
Multiply
Add terms
Multiply
Find the width of the prism by using the known volume of the prism and the formula for the volume of a rectangular prism. Then, use the formula for the surface area of a rectangular prism.
Substitute values
Multiply
Commutative Property of Multiplication
Rearrange equation
LHS/2.8=RHS/2.8
Use a calculator
Substitute values
Multiply
Add terms
Multiply
b=7, h=2.3
Multiply
b1⋅a=ba
Calculate quotient
Substitute values
Multiply
Add terms
Use the formula for the surface area of a prism and the given surface area to find the height of the prism. Then, find the volume of the prism.
b=4, h=2.7
Multiply
b1⋅a=ba
Calculate quotient
Substitute values
Multiply
LHS−10.8=RHS−10.8
Rearrange equation
LHS/11.5=RHS/11.5
Calculate the volume or surface area of the triangular or rectangular prism given the base area B, the height, and the side length of the base. The base is always a regular polygon. Round the answer to one decimal place if necessary.
Use the general formula for the volume of a prism to calculate the volume of the triangular prism. Then, use the formula for the volume of a rectangular prism to find the volume of the rectangular prism. Compare the volumes.
There are two possible shapes of the dog house for Bubbles. To determine which one offers the most space for the dog, each of their volumes should be calculated.
h=1, b=1.2
1⋅a=a
b1⋅a=ba
Calculate quotient
Finally, the volumes of the prisms can be compared.
Volume of the Triangular Prism | Volume of the Rectangular Prism |
---|---|
1.2 in.3 | 1.6 in.3 |
The volume of the rectangular prism is greater than the volume of the triangular prism. This means that the dog house in the shape of the rectangular prism is more spacious, so Mark should choose that one.
The toy company Mini Beach Makers makes rectangular sandboxes that measure 7 feet by 6 feet by 1.2 feet. Ali's father buys a sandbox and 45 cubic feet of sand for his children.
We need to figure out whether 45 cubic feet of sand will completely fill up a sandbox that measures 7 feet by 6 feet by 1.2 feet. Let's start by drawing the sandbox!
The volume of a three-dimensional figure is the measure of space that it occupies expressed in cubic units. Notice that the volume of the sandbox is equal to the volume of sand that will fill the sandbox. Since we know that the sandbox is rectangular, we can find its volume V by multiplying its length l, width w, and height h. V= l w h For this sandbox, l = 7, w= 6, and h= 1.2. Let's substitute these values into the formula to calculate the volume of the sandbox!
The volume of the sandbox is 50.4 cubic feet. Now we can compare this volume with the volume of sand purchased by Ali's father. ccc Volume of & & Volume of sand purchased the sandbox & & by the customer [0.5em] 50.4ft^3 & > & 45ft^3 The volume of sand purchased by Ali's father is less than the volume of the sandbox. This means that the sand will not completely fill up the sandbox.
We are asked to determine the surface area of the sandbox that should be painted yellow. Note that the sandbox does not have a top and the bottom does not have to be painted. This means that the only part of the sandbox that needs to be painted are the lateral surfaces. In other words, the area to be painted is equal to the lateral area of the rectangular prism.
\begin{gathered}
S_\text{sandbox}=Ph
\end{gathered}
The lateral area of a prism is the product of the perimeter of the base P and the height of the prism h. The base of the sandbox is a rectangle with a length of 7 feet and a width of 6 feet. Its perimeter can be found by the following formula.
P=2(w+l)
Let's substitute l= 7 and w= 6 into the formula to find P.
The perimeter of the sandbox is 26 feet. Let's multiply it by the height of 1.2 feet to calculate the surface area of the lateral faces of the sandbox.
We found that Ali's father needs to paint an area of 31.2 square feet.
Jordan is mailing her aunt a package.
We can determine the amount of cardboard used to create the shipping container by finding the surface area of the package. We can see that it has the shape of a triangular prism.
Let's recall the formula for the surface area of a prism. S=2B+Ph Here, B is the base area, P is the base perimeter, and h is the height of the prism. Let's start by calculating the base area B. Since the base is a triangle, we can use the formula for the area of a triangle. A=1/2bh From the diagram, we know that b= 6 and h= 4.5. Let's substitute these values into the formula and solve for A.
The area of the triangular base of the prism is 13.5 square inches. Next, let's find the perimeter of the base by adding all the side lengths together. P=5.4+5.4+6=16.8inches Now we have enough information to find the surface area of the prism. Let's substitute 13.5 for B, 16.8 for P, and 14 for h into the formula for the surface area of a prism and evaluate S.
We found that the surface area of the prism is 262.2 square inches. This means that Jordan used 262.2 square inches of cardboard to create the shipping container.
Dylan is constructing a die. He wants the side of the die to be 4 centimeters long.
We need to find how much empty space there will be inside the box. The die is in the shape of a cube. Let's recall that the volume of a cube with a side length s can be found by raising s to the power of 3. V=s^3 We know that the side length of the die Dylan is making is 4 centimeters. Let's substitute 4 for s and evaluate V.
The volume of the die — and the amount of empty space inside the box — is 64 cubic centimeters.
Now we can determine how much red paper material Dylan needs to make the die by calculating the surface area of the die. Let's remember the formula for the surface area of a cube. S=6s^2 Let's substitute 4 for s again and solve for S.
The surface area of the die is 96 square centimeters, which means that Dylan needs 96 square centimeters of red paper material.
Find the surface area of the regular hexagonal prism.
We want to find the surface area of the given regular hexagonal prism.
Remember that surface area is the total area of all the surfaces of a three-dimensional figure. The surface of a solid includes lateral surfaces and bases. Let's draw a net of the prism to see all surfaces of the figure.
The surface of the figure includes 6 identical rectangular lateral faces and 2 identical hexagons for its bases. The sum of the area of these rectangles and hexagons gives us the total surface area of the given figure. Let's calculate the area of each figure one at a time.
We can find the area of a rectangle by multiplying its length by its width. In this case, the length is 13 centimeters and the width is 5 centimeters.
Let's multiply these dimensions to find the area! A_r=13 * 5 ⇓ A_r= 65cm^2 The area of each identical rectangle is 65 square centimeters.
Notice that we can divide a regular hexagon into 6 identical triangles.
This allows us to calculate the area of the hexagonal base by multiplying the area of one triangle by 6. Let's use the formula for the area of a triangle! A_t=1/2bh In this formula, b is the base length and h is the height of the triangle. In our case, the base is 5 centimeters and the height is 4.3 centimeters.
The area of each triangle is 10.75 square centimeters. Now, we will multiply this number by 6 to determine the area of the hexagonal base B. B=6(10.75) ⇓ B= 64.5cm^2 The area of each bases is 64.5 square centimeters.
Now that we have the area of all the faces, we can calculate the surface area of the prism by adding all of them together. Since there are 6 identical lateral rectangular faces, we can multiply the area of the rectangle by 6. Similarly, we can multiply the area of the hexagon by 2 as there are 2 hexagonal bases. SA= & 6* 65+ 2 * 64.5 ⇓ & SA= & 519cm^2 The surface area of the regular hexagonal prism is 519 square centimeters.