Forces
The Free High School Science Texts: A Textbook for High School Students Studying Physics.
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TO DO LIST - Definition - Diagrams - Equilibrium of Forces - Newton's Laws of Motion - Newton's Law of Universal Gravitation - Examples - Important Quantities, Equations, and Concepts

Summary of Important Quantities, Equations and Concepts

**Table 4.1:** Summary of the symbols and units of the quantities used in Force
Units
Quantity	Symbol	S.I. Unit	Fundamental Units	Direction
Mass	m	kg	kg	no
Acceleration	${\overrightarrow {a}}$	m·s⁻²	m·s⁻²	yes
Force	${\overrightarrow {F}}$	N	kg·m·s⁻²	yes

Equilibrium: Objects at rest or moving with constant velocity are in equilibrium and have a zero resultant force.

Equilibrant: The equilibrant of any number of forces is the single force required to produce equilibrium.

Triangle Law for Forces in Equilibrium: Three forces in equilibrium can be represented in magnitude and direction by the three sides of a triangle taken in order.

Newton's First Law: Every object will remain at rest or in uniform motion in a straight line unless it is made to change its state by the action of an external force.

Newton's Second Law: The resultant force acting on a body results in an acceleration which is in the same direction as the resultant force and is directly proportional to the magnitude of this force and inversely proportional to the mass of the object.

Newton's Third Law: For every force or action there is an equal but opposite force or reaction.