Question

newtons 2nd law of motion is also called the law of acceleration. this law states that force equals mass times acceleration. it is a mathematical equation and is written like this: f = mass × acceleration.
the mass of an object is the amount of matter in the object and acceleration is when an object speeds up, slows down, or changes direction. when mass is increased, the amount of force used to accelerate the object must be increased and when mass is decreased, the amount of force required to accelerate the object is decreased.
what defines the amount of matter in an object?
its mass
its volume
its weight

Explanation:

The text directly states "The mass of an object is the amount of matter in the object".

Answer:

its mass