Sound — Science STD 8 — Question

Why have synthetic fibres become more popular than natural fibres?

How can a very heavy machine be moved conveniently from one place to another in a factory? (No crane is available for this purpose).

What is the difference between a meteor and a meteorite?

Element A is soft, brittle and does not conduct electricity. Element B is hard, malleable and 'ductile; and also conducts electricity. Which of the two elements, A or B, is a non-metal?

Explain why, a glass rod can be charged by rubbing when held by hand but an iron rod cannot be charged by rubbing, if held by hand.

Boojho while waving his hand very fast in front of his eyes, observes that his fingers appear blurred. What could be the reason for it?

Explain the discovery of penicillin and its significance in treating bacterial infections, including the issue of antibiotic resistance.

We should plant trees and nurture the ones already present in the neighbourhood. Why?

Imagine Earth’s magnetic field suddenly disappeared. What kinds of problems could arise for life on Earth? Explain.

During adolescence, the body of boys and girls undergoes certain changes. Given below are few of those changes
(a) Broad shoulders
(b) Wider chests
(c) Wider region below waist
(d) Development of muscles
(e) Development of mammary glands
(f) Growth of facial hair
(g) Acne and pimples on face
(h) Development of sex organs
(i) High-pitched voice
(J) Growth of pubic hair
Categorise these changes into those that occur in boys and those that occur in girls and fill in the table given below.
Body changes during adolescence

Boys	Girls