The Physics
Hypertextbook
Opus in profectus

# Force and 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 = ma

• 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, named after the English physicist and mathematician Isaac Newton (1642–1727).

[N = kg m/s2]

• Supplementary Materials