Coal and petroleum — Science STD 8 — Question

Define asexual reproduction. Name two methods of asexual reproduction in animals. Name two animals which reproduce by these asexual reproduction methods.

Explain why, a wide steel belt is provided over the wheels of an army tank.

Define manure. What are the advantages of manure?

A student makes a device P by using three long and narrow strips of plane mirrors inclined at 60° to one another which enables him to see beautiful patterns made by pieces of coloured glass bangles. On the other hand, another student makes a device Q by using two plane mirrors arranged parallel to each other which helps him to see a football match clearly even when some very tall persons are sitting in front of him in the ground. What are P and Q?

Choose the thermoplastics and thermosetting plastics from the following:
Melamine, Polythene, Bakelite, Polyvinyl chloride.

What are the conditions necessary for combustion to take place?

What makes things visible to us? Why cannot we see a book which is placed.
(a) Behind a wooden screen, and (b) In a dark room?

Explain why, wooden (or concrete) sleepers are kept below the railway line.

What will happen if the natural habitat of a wild animal is destroyed?

What is meant by saying that force is due to an interaction'? Give an example to illustrate your answer.