Newton’s Second Law of Motion is also known as the Law of Acceleration. According to this law, F=ma where F is the force being applied to the object, m is the mass of the object, and a is the acceleration experienced by the object. When all other variables are equal, the greater the force, the greater the acceleration. When all other variables or equal, the greater the mass, the less the acceleration. This explains why greater force is required to move an object with greater mass.
What does this mean? Imagine a pool table. The mass of the pool balls is identical from ball to ball. If you hit the ball softly with the tip of the cue, the ball will travel slowly. If you slam the ball with the tip of the cue, the ball will travel quickly. The difference in the acceleration is not due to the mass. It is due to the force being applied. In this case, the formula would be a=F/m.
You know from personal experience that the force required to roll a solid marble ball that is as large as you, is a lot greater than the force required to roll a bowling ball. This is an example of the part of the law that states that, all else being equal, the greater the mass, the less the acceleration. Why? Because it takes more force to get and keep the object with greater mass moving. And size is not always a reliable indicator of mass. If the objects being compared were a styrofoam ball as large as you and a bowling ball, the acceleration of the bowling ball would be slower than the acceleration of the styrofoam ball when an identical force was applied. Why? Because the mass of the bowling ball is greater than the mass of the styrofoam ball.
By the way, you can use Newton’s Second Law of Motion to find the mass of an object if you know the force applied and the acceleration experienced by the object. How? F/a=m where the mass of an object can be calculated by dividing the force applied to the object by the acceleration experienced by the object.
This law is important because it explains the relationship between mass, acceleration, and force. It is one of the basic laws of physics.
More on this topic: Modeling Ships and Space Craft: The Science and Art of Mastering the Oceans and Sky by Gina Hagler — Part II – Evolution of Theory, Chapter Four – Hydrodynamic Theorists and Part III – Scale Model Testing Begins, Chapter Ten – It is Rocket Science