What does the mass of a body measure?

Newton's first law of motion describes the following:

$A$ girl jumps down from a moving bus,along the direction of motion of the bus,tilting slightly forward. She falls on $(a)$ a sheet of ice $(b)$ a patch of glue. Which of the following statements is correct regarding her fall?

An object is moving with a constant speed along a straight-line path. $A$ force is not required to

Write and explain Newton's first law of motion.

What is dynamics? What is mechanics?