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Mass
Forces diagram
When an object is at rest, the forces acting upon it are balanced - there are no unbalanced forces.
That's the 'resultant' of all the forces, and the 'net force' on the object.
Newton's first law describes something special that results from the sum of all the external forces (including gravity) on an object. The forces exerted by the object on other things or on itself are irrelevant to that result, and so the free body diagram used to calculate that result gives the correct result even though we completely neglect forces exerted by the body. Why is Newton's first law important? That's a different question (see below).
Action-Reaction Forces.
The force exerted on a scale by an object and other forces acting.
un-accelerated
Mass
Forces diagram
When an object is at rest, the forces acting upon it are balanced - there are no unbalanced forces.
That's the 'resultant' of all the forces, and the 'net force' on the object.
However many there are exerted on the object. Usually there is gravity, friction, and another force exerted on the object.
Inertia.
Newton's first law describes something special that results from the sum of all the external forces (including gravity) on an object. The forces exerted by the object on other things or on itself are irrelevant to that result, and so the free body diagram used to calculate that result gives the correct result even though we completely neglect forces exerted by the body. Why is Newton's first law important? That's a different question (see below).
Forces are exerted on a submerged object due to water pressure not being balanced due to buoyancy. This is when the pressure at the bottom of the submerged object is greater than the fluid on the top of the object, thus projecting the object upward.
The "reaction" force.