Force and pressure. — Science STD 8 — Question

Name the two types of substances which are added to the fields by the farmers to maintain the fertility of soil.

Name any two types of chemicals used in agriculture which cause water pollution.

One student says that water exerts pressure on the bottom of the bucket but another student says that water exerts pressure on the sides of the bucket. What would you like to say?

If you want to hear a train approaching from far away, why is it more convenient to put the ear to the track?

How will you reduce friction between those machine parts which rub against each other? Give the simplest method.

Name any four places in India where petroleum is found.

What is the length of vocal cords in a man?

Name one crop which can tolerate standing water (water-logging) in the field and one which cannot.

A highly poisonous animal Z which inhabits crop field is commonly known as friend of the farmer. It eats up pests like Y and saves the crops from damage.
The animal X is killed in large numbers to get its Z which sells in the market at a high price. What is X, y and Z?

Name the organelle of a plant cell where photosynthesis takes place.