When an object moves or remains at rest in a straight light, unless that state is changed by a resisting force. This state is called inertia. Such as when a car comes to a sudden halt the driver who wears a seat belt comes to a halt as well. This is the action of inertia.
Mass is total matter in a body. It is measured in Kilograms.Mass is measured by a beam balance. It remains constant no matter where the object is. Weight is opposite of mass. It is the pull on earth by gravity. calculated by multiplying gravity and mass: Weight=mass(gravity).
It is the amount of particles in an object. It is defined as mass per volume: Density= mass/volume