Tasneem wants to make a metre scale by herself. She considers the following materials for it—plywood, paper, cloth, stretchable rubber and steel. Which of these should she not use and why?
Tasneem should not use cloth and stretchable rubber for making a metre scale.
Cloth is flexible and can stretch or shrink depending on tension and moisture, leading to inaccurate measurements.
Stretchable rubber can expand and contract easily, causing inconsistent measurements.
Steel, plywood, and paper are better choices because they maintain their length and do not stretch under normal conditions.
Steel is especially good as it is rigid and durable.
Paper and plywood, if kept dry and handled carefully, can provide reasonably accurate measurements.
Explanation
The chapter emphasizes on Page 3-4 that standard units must give consistent measurements that do not differ from person to person. A good measuring scale must maintain its length and not stretch or shrink. Materials like cloth and rubber change their length when pulled or stretched, making them unsuitable for accurate measurement.
Solution Steps
Identify that cloth and stretchable rubber should not be used for a metre scale.
Explain that cloth is flexible and changes size due to tension and moisture, causing inaccurate measurements.
Explain that stretchable rubber expands and contracts easily, leading to inconsistent measurements.
Identify steel, plywood, and paper as better choices because they maintain their length.
Note that steel is rigid and durable, making it an especially good choice.
Mention that paper and plywood can be accurate if kept dry and handled carefully.