Which Newton's law of motion is applied in the flight of a bird?

Why is glass or chinaware packed with straw?

Newton's first law of motion is also called the law of inertia. Why?

Quick sand consists of very smooth and tiny grains of sand. What would happen if a man or a heavy animal steps over a patch of such sand in a desert?

$(a)$ $(i)$ Define momentum. State its $SI$ unit.
$(ii)$ An object of mass $50 \ kg$ is accelerated uniformly from a velocity of $4 \ m/s$ to $8 \ m/s$ in $8 \ s$. Find the magnitude of the force exerted on the object.
$(b)$ State Newton's first law of motion.

$(i)$ Name the property by virtue of which a body resists a change in its state of motion. Name the physical quantity which is a measure of this property.
$(ii)$ Explain why some of the leaves may get detached from a tree if we vigorously shake its branch.