Q1:- Why does a balloon filled with hydrogen rise in air?

Ans:- As the weight of the balloon is less than the weight of air displaced by it therefore the balloon rises in air. In balloons hydrogen is normally filled because it is lighter than air.

Q2:- Why does smoke curl up in the air?

Ans:- This is another case of lighter weight. Smoke contains hot gases which are lighter in weight , follow a curved path because of the eddy currents that are set up in the air.

Q3:- Why does an electric bulb explode when it is broken?

Ans:- The bulb is a partial vacuum ,and as it breaks , air rapidly enters in resulting in a small explosion.

Q4:- Why does a person fall forward when he jumps out of a running train or bus?

Ans:- According to the Newton’s first law, a body at rest will remain at rest and body in uniform motion until and unless some external force is applied on it.

The person is in motion while in the train or bus. When he jumps out, his feet come to rest while touching the ground but his upper portion which is still in motion that moves him forward.

Q5:- Why is compass used as an indicator of direction?

Ans:- The magnetic needles of a compass under the influence of the earth’s magnetic field lie in a north-south direction . Hence we can identify direction.