College Physics II – Mechanics, Sound, Oscillations, and Waves
Definition
Net external force is the vector sum of all external forces acting on an object. It determines the object's acceleration according to Newton's Second Law.
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Net external force is calculated by adding all external forces as vectors, taking both magnitude and direction into account.
According to Newton's Second Law, the net external force acting on an object is equal to the mass of the object multiplied by its acceleration: $F_{net} = ma$.
If the net external force on an object is zero, it will either remain at rest or continue moving at a constant velocity (Newton's First Law).
The unit of net external force in the International System of Units (SI) is the newton (N), which is equivalent to $kg \cdot m/s^2$.
Friction, gravity, tension, and normal forces are common types of external forces that can contribute to the net external force.
Review Questions
How do you calculate the net external force acting on an object?
What does Newton's Second Law state about net external force?
What happens to an object's motion if the net external force on it is zero?
Related terms
Newton's First Law: An object at rest stays at rest and an object in motion stays in motion with a constant velocity unless acted upon by a net external force.
Newton's Second Law: $F_{net} = ma$, where $F_{net}$ is the net external force, $m$ is mass, and $a$ is acceleration.
Newton's Third Law: For every action, there is an equal and opposite reaction.