We see chairs made up of various materials, such as wood, iron, plastic, bamboo, cement and stones. Following are some desirable properties of materials which can be used to make chairs. Which materials used to make chairs fulfil these properties the most?
Hardness (does not bend or shake on sitting even after long use).
Iron, cement, and stone chairs are the hardest and most suitable for this property. These materials are difficult to compress or scratch and do not bend easily under weight.
Lightweight (easy to lift or to take from one place to another).
Plastic and bamboo chairs are lightweight and easy to move from one place to another. These materials have less mass compared to iron, cement, or stone.
Does not feel very cold when sitting during winters.
Wood, plastic, and bamboo chairs do not feel very cold during winters. These materials are poor conductors of heat and do not absorb body heat quickly, unlike iron which feels cold to touch.
Can be cleaned regularly and made to look new even after long use.
Plastic and iron chairs can be cleaned easily and maintained. Plastic chairs can be wiped clean and retain their appearance. Iron chairs can be painted to look new, though they may require protection from rust. Wood and bamboo require more care to prevent damage from moisture.
Explanation
(i) The chapter defines hard materials on Page 7 as those which are difficult to compress or scratch. Iron, cement, and stones are hard materials that do not bend or shake on sitting. (ii) The chapter discusses mass on Pages 12-13, explaining that lighter objects have less mass. Plastic and bamboo are lightweight materials suitable for portable furniture. (iii) While not explicitly covered in this chapter, the concept relates to thermal properties. Wood, plastic, and bamboo are insulators that do not conduct heat away from the body quickly. (iv) The chapter mentions on Page 7 that some metals may lose their lustre due to air and moisture. Plastic materials are generally easier to clean and maintain compared to natural materials like wood and bamboo.