Science Que-Ans (Each of 2 Mark )

Luggage on the top of the bus is a loose fixture and not a compact part of the bus. Thus, when a speeding bus brakes suddenly, the luggage continues moving forward because of inertia of motion and is likely to fall off the bus. Conversely, if a stationary bus accelerates suddenly, the luggage continues in the same state because of inertia of rest and hence is left behind relative to bus such that it falls backward. To avoid the falling of luggage, it is tied with a rope.

a. Jet airplanes and rockets work on the principle of Newton's third law of motion. In this case, the hot gases come out of a nozzle (a fine opening) with a great force, i.e., action and the rocket moves with high speed upwards as a reaction.
b. If we fill a balloon with air and hold it with its mouth downwards, then when we release the balloon, the air rushes out vertically downwards (action). *The balloon moves vertically upwards (reaction).

c. When a gun is fired, the bullet goes out (action) due to the force applied on it. According to Newton's third law of motion, the gun recoils backward due to the reaction acting on it in the opposite direction.

Thoroughly dry a glass beaker and take some crushed ice in it. After sometime, droplets of water appear on the outer surface of glass. It is because of water vapours present in air, which get condensed when they come in contact with the glass surface where the temperature is very low.

The increasing order of density for the given substances is:
Air, exhaust from chimneys, cotton, water, honey, chalk, iron. Actually, the density of a substance depends upon the number of particles per unit volume as well as upon their mass. The number of the particles is related to their size as well as the attractive forces among them.