The principles of physics are the foundation of physics, and refer to the basic concepts that describe movement and interaction of matter.
The principles of mass, weight, energy and power are among these principles.
Mass is the amount of matter an object has, and is measured in kilograms. A simple rule is that a heavier object will have more inertia, which means it will resist changes in its movement. An example would be a golf ball, which is much heavier than a baseball, due to the force of gravity.
Weight is the force of gravity acting on an object, and is measured in newtons. Gravity is a constant force that always acts on objects, so weight is a measure of mass and gravity.
Energy is the capacity of an object to perform work, and is measured in joules. Energy can be transformed from one form to another, as in an internal combustion engine where the energy from the fuel is converted into kinetic energy.
Power is the amount of work an object can do in a period of time.