This is a Level 3 Geometry activity from the Figure It Out Series.
A PDF of the student activity is included.
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- Predict the shape formed when three-dimensional objects are 'sliced'.
- Plasticine or play dough
- A knife
- FIO, Level 3, Geometry, Slce of Life, pages 16-17
Predicting results is an important part of this activity.
The angle that the cut is made on will affect the shape of the section. For example, a cut that is at right angles to the axis will give a circle as the cross section of a cone and a cylinder.
These right-angled cuts are much easier to predict than those that are slanted. When a slanted cut is used, the section is very much influenced by how and where the cut is made. A cut through a circle-based cone at a slant will give an ellipse as a section.
A parabola is formed by cutting through a circle-based cone parallel to a sloping side.
Examples of a parabola shape are:
- the path followed by a ball in flight
- the shape of wires supporting a suspension bridge.
Answers to Activity
1-3. Practical activities
4. The sections should look like this:
5. Practical activity