122
Circle and cylinder
Textbook: Part 4, lesson 122, pp. 43–45
GoalCircle and cylinder: how a cylinder is formed; its bases and lateral surface.
New words
cylinder · silindrbase · asoslateral surface · yon sirtheight · balandlik
Explanation
If a rectangle spins about one of its sides, it forms a cylinder. The side that is the axis becomes the height of the cylinder, and the other side becomes the radius of the base circle. A cylinder has two equal circular bases and a curved lateral surface. A can, a pipe and a glass are cylinder-shaped.
Worked examples
A 3 cm × 7 cm rectangle spun about its 7 cm side gives a cylinder with height 7 cm, base radius 3 cm and base diameter 6 cm.
A cylinder has 2 flat bases and 1 curved surface.
Class activity
“Spin and see”: spin a paper rectangle stuck on a thin stick quickly and watch the cylinder shape appear.
Practice
1
How many flat bases does a cylinder have?
2
2
A 3 cm × 7 cm rectangle is spun about its 7 cm side. What is the diameter of the cylinder's base in cm?
6
3
Which of these is cylinder-shaped: a ball, a tin can, a matchbox?
the tin can
4
A cylindrical barrel holds 50 l. 8 l was poured in 4 times. How many more litres are needed?
18
5
A rectangle with sides 4 cm and 9 cm is spun about its 4 cm side. What is the radius in cm of the base of the cylinder formed?
9