What it shows
Two parallel straws cut by a third straw make eight angles, and the model shows that corresponding angles and alternate angles are equal while co-interior angles add up to 180 degrees. Turning one straw so the lines are no longer parallel breaks these rules.
The science
When a transversal cuts two lines, it makes pairs of angles. Corresponding angles lie in the same position at each intersection and are equal if the lines are parallel. Alternate interior angles are on opposite sides of the transversal between the lines and are also equal. Co-interior angles lie on the same side between the lines and add up to 180 degrees. These facts come from the idea that sliding one line along the transversal to the other leaves its direction unchanged, so the angles are the same.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Three long straws or ice cream sticks of different colours
- A cardboard sheet 30 cm by 20 cm
- Paper fasteners or pins with clay
- A protractor
- A ruler
- Markers
Safety
For this project: An adult should push the paper fasteners through the card and cover any sharp ends with tape.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Fix two straws on the card as parallel lines 6 cm apart using paper fasteners at the ends, and check that the distance is the same at the two ends.
Fix the third straw across both at a slant with a fastener at each crossing, so that it can still turn a little.
Mark the angles 1 to 8 with a marker on the card, starting from the top left of the upper crossing.
Measure all eight angles with the protractor and write them in a table. Measure carefully from the same side every time.
Mark pairs of equal angles with the same colour and list which are corresponding, alternate, vertically opposite and co-interior.
Add the co-interior pairs and write that they come to 180 degrees.
Loosen the fasteners and tilt one parallel straw slightly so the distance at the ends is no longer equal, and measure the angles again to see that the equalities fail.
Display the table next to the model and write the three rules.
What you should see
For parallel lines, corresponding and alternate angles match within 2 degrees and co-interior angles sum to 180 degrees, while the tilted straw breaks all three rules.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What are corresponding angles?
Angles in the same position at the two crossings of the transversal.
2What is the sum of co-interior angles for parallel lines?
180 degrees.
3What are vertically opposite angles?
Angles opposite each other at a crossing, always equal.
4How can you test whether two lines are parallel using a transversal?
If corresponding angles are equal, the lines are parallel.
Take it further
Use the rules to find the angles in the frame of a window grille or a railway track picture.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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