Question

According to Galileo, this quantity is not needed to keep a body in motion under ideal conditions.

Answer 1

This condition is called Galileo's Law of Inertia which states that all bodies accelerate at the smart rate , no matter what are their masses or size. Inertia is that tendency of matter to resist changes in its velocity. Isaac Newton's first law of motion captures the concept of inertia.

Answer 2

According to Galileo, quantity does not matter under ideal conditions. The ideal conditions to experiment under is when there is no air resistance only then it can be seen that the statement is true i.e. quantity is not a factor

If you drop a ball and a feather under the ideal condition i.e. no air resistance you will see that both the ball and feather which weigh different will fall at the same time