What is conservation of linear momentum? Under what conditions can this concept be applied?

What are internal and external forces?

“Forces always occur in pair.” From which law, do we conclude the above statement. Give two examples to support your answer.

“Action and reaction are equal and opposite, still their resultant is not zero.” Explain.

Place a water filled tumbler on a tray. Hold the tray and turn around as fast as you can. We observe that the water spills. Why?

Two children $\mathrm{A}$ and $\mathrm{B}$ wearing skates face each other. $\mathrm{A}$ has a bag full of sand. He throws the bag towards $\mathrm{B}$. $\mathrm{B}$ catches it. What will you observe?

Suspend a good quality glass test tube containing some water by two strings on a stand as shown. Place a stop cork at the mouth of it. Start heating the test tube as shown below. What will you observe after some time?

State the action and reaction in the following:

Moving rocket

State the action and reaction in the following:

Firing of a bullet from a gun