Parallel lines and angles: a road across two streets
Turn a diagonal road across two parallel streets and compare the angles it makes at both crossings.
Core concept
When a transversal crosses parallel lines, corresponding and alternate angles are equal and co-interior angles add up to 180°
Topic: Parallel lines and a transversal
In a town, two straight streets run side by side without ever meeting: they are parallel. A diagonal road, the transversal, crosses both. At each crossing it makes four angle: The amount of turn between two lines that meet, measured in degrees (°). All key words. Angles in the same position at the two crossings are corresponding angles. Angles between the streets on opposite sides of the road are alternate angles; those on the same side are co-interior angles. Angles opposite each other at one crossing are vertically opposite.
What you will learn
- Name corresponding, alternate, co-interior and vertically opposite angles.
- Use the angle facts for parallel lines to find unknown angles.
- Explain why the facts fail when the lines are not parallel.
Before you start
- Angles on a straight line add up to 180°.
Materials
- A map of a town with parallel streets
Equipment
- A ruler and a protractor
Procedure
- Drag the diagonal road to turn it.
- Tap the blue chip to choose a pair of angles; read both angles.
- Record corresponding, alternate and co-interior angles with parallel streets.
- Tap the green chip to tilt Street B, and record a pair that no longer follows the rule.
How this simulation is simplified
- The streets and the road are straight lines.