Editing Net force (section)

{{short description|Vector sum of all forces acting upon a particle or body}}
[[File:Free body diagram.png|alt=A block rests on an inclined plane, with its weight (W) acting downwards, normal reaction (N) acting perpendicular to the slope, and friction (F) acting parallel to the slope|frame|A [[free body diagram]] of a block resting on a rough inclined plane, with its weight (W), normal reaction (N) and friction (F) shown.]]

In [[mechanics]], the '''net force''' is the sum of all the [[force]]s acting on an object. For example, if two forces are acting upon an object in opposite directions, and one force is greater than the other, the forces can be replaced with a single force that is the difference of the greater and smaller force. That force is the net force.<ref>{{cite web |title=University Physics Volume 1 |url=https://openstax.org/books/university-physics-volume-1/pages/5-1-forces |website=openstax.org|date=19 September 2016 }}</ref>

When forces act upon an object, they change its [[acceleration]]. The net force is the combined effect of all the forces on the object's acceleration, as described by [[Newton's laws of motion|Newton's second law of motion]].

When the net force is applied at a specific point on an object, the associated [[torque]] can be calculated. The sum of the net force and torque is called the '''[[resultant force]]''', which causes the object to rotate in the same way as all the forces acting upon it would if they were applied individually.<ref>Symon, Keith R. (1964), Mechanics, Addison-Wesley, {{LCCN|605164}}</ref>

It is possible for all the forces acting upon an object to produce no torque at all. This happens when the net force is applied along the [[line of action]].

In some texts, the terms ''resultant force'' and ''net force'' are used as if they mean the same thing. This is not always true, especially in complex topics like the motion of spinning objects or situations where everything is perfectly balanced, known as [[static equilibrium]]. In these cases, it is important to understand that "net force" and "resultant force" can have distinct meanings.

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This discussion of forces on a particle and rigid body is confusing:

A acting on an object may cause changes in the motion or in the shape (configuration) of the object. When two or more forces are acting on an object, the concepts of net force and resultant force are intended to simplify description of their effect on its motion.

If the forces are acting on a [[Part]] (the size of the object is so Tinsie Winnsie that it can be approximated by a point), they can only change its [[velocity]]. In that case, there is no difference between the net force and the resultant force because no rotation is associated with such objects.<ref>{{cite web |title=University Physics Volume 1 |url=https://openstax.org/books/university-physics-volume-1/pages/2-3-algebra-of-vectors |website=openstax.com}}</ref>

If the object is an extended but [[rigid body]] (no change in shape), the forces can change its velocity (i.e. the velocity of its [[center of mass]], usually called its linear velocity) as well as its [[angular velocity]]. In that case, it may be useful to distinguish the resultant force from the net force. And even in the case of non-rigid objects (deformable bodies or systems), the concepts of net and resultant force are equally applicable to description of their overall motion.
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