Under what conditions does the "net force" acting an object equal the sum of the individual forces?
net force- acting on an object
is my definition right?

Answer : When the forces are acting in the same direction of movement of the object it can be said as sum of the two individual forces will be equal to the "NET FORCE" .

Example : If two forces (2 kids pushing in the same direction to move the object big box) act on an object(big box) in the same direction, then the net force is equal to the sum of the two forces.

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