A prism is a shape which has the same cross section throughout its height.
By this I mean if you cut a prism, it may get smaller but the overall shape stays the same.
Here are some examples
If you sliced through these cross section of these shapes, they would get smaller but the overall shape would stay the same.
Cross sections of the shapes above are a circle, triangle, square and rectangle
The cross section is the shape of the face of the prism.
How do I find the volume ? They are all different shapes.
Ah yes, yet another formula to learn.
Volume of a prism = area of the cross section x height
Before we continue we need a recap of how to find the area of these shapes.
Area of a square = base x height
Area of a rectangle = base x height
Area of a triangle = base x height ÷ 2
Area of a circle = π x r x r
Can you remember the value of π ? Don't worry you will find out later if you have forgotten.
Almost there. To find the volume we calculate the area of the face first, and then multiply by the height.
Time to practice
Find the volume of this box of chocolates. Base = 6 cm?
The face (cross section) is a square - find the area first.
6 x 6 = 36 cm, now just multiply by the length, which as its a square box is also 6 cm. 36 x 6 = 216 cm³
Find the volume of the cornflakes box. Base 12 cm, height 6 cm, length 30 cm
The face (cross section) is a rectangle - find the area first.
12 x 6 = 72 cm, now just multiply by the length 72 x 30 = 2160 cm³
Find the volume of the triangular prism. Base 4 cm, height 4 cm, length 12 cm
The face (cross section) is a triangle - find the area first.
4 x 4 = 16 ÷ 2; = 8 cm, now just multiply by the length 8 x 12 = 96 cm³
Find the volume of this can. Radius 4 cm, length 8 cm.
The face (cross section) is a circle - find the area first.
Did you remember the value of π, of course 3.142
Area = 3.142 x 4 x 4 = 50.27
Now multiply by length 50.27 x 8 = 402.16 cm³
That was a bit of a marathon wasn't it. Guess what,it is not over...