Force & Mass

Summary

Newton's second law of motion (also known as the force law) states that …
- acceleration is directly proportional to net force when mass is constant, and …
- acceleration is inversely proportional to mass when net force is constant, and consequently …
- net force is directly proportional to mass when acceleration is constant.
Newton's second law of motion is more compactly written as the equation …
∑ F = m a
Mass
- Mass is a measure of resistance to acceleration.
  (More generally, mass is a measure of resistance to all sorts of change.)
- Mass is a scalar quantity associated with matter.
- When a system is composed of several objects it is the total mass that matters.
- The SI unit of mass is the kilogram [kg].
Force
- A force is an interaction that causes acceleration.
  (More generally, a force is an interaction that causes a change.)
- A force is a vector quantity associated with an interaction.
- When several forces act on a system it is the net, external force that matters.
- The SI unit of force is the newton [N = kg m/s²].
Supplemental Materials
- Summary as a concept map [pdf]
- Original statement in Latin from Newton's Principia with English translation