Recognition of Solids
67. Meet the Cylinder · Two flat faces, one curved side
Top and bottom faces remain parallel and identical as height changes.
A cylinder is a 3D solid with two parallel circular faces (top and bottom) of equal size, connected by a curved surface. Think of a tin can or a roller.
What this lesson covers
Try to break it
Let's peel it apart! The top and bottom are identical circles. The side unrolls into a rectangle. Notice how the height changes but the faces stay the same.
How you build it
Construct a cylinder.
- Draw the bottom circular face — click a point near the bottom, then click outward to set its size.
- Draw the top circular face directly above the first one. It comes out the same size automatically — a cylinder has two equal circular faces.
- Draw a straight line joining the left edge of the bottom circle to the left edge of the top circle.
- Draw a straight line joining the right edge of the bottom circle to the right edge of the top circle. This completes the cylinder.
The proof, step by step
Prove that the solid is a cylinder with two identical, parallel circular faces.
- A cylinder has two identical flat circular faces (top and bottom).
- It has one curved surface that connects the two circular faces.
- It has no vertices (corners), but has two edges where the curved surface meets the flat faces.
Worked example
A solid has two identical circular flat ends and one curved surface. It has no vertices. What is this solid called?
A cylinder is defined by two identical parallel circular bases connected by a curved surface. It has 0 vertices, 2 edges, and 3 faces.
- Cone
- Cylinder — correct
- Sphere
- Cuboid