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Net Force on One Body

Also known as sum of forces · resultant force · unbalanced force · sigma F · ΣF · driving force minus friction

Fnet=F1−F2F_{\text{net}} = F_1 - F_2

Worked example: 250 N push against 80 N friction → 170 N net — press Try an example to run it live, then adjust anything.

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See also
Newton's Second Law — What the net force is for: F = ma turns it into the acceleration the body actually gets.Kinetic Friction Force (f = μₖN) — The usual source of the opposing F₂, from the normal force and the coefficient of friction.Weight (W = mg) — The other force that is almost always in the sum, whenever the motion is vertical.

Learning zone

Newton's second law asks for the net force, and nearly every wrong answer in a first mechanics course comes from feeding it the applied one instead. A worker shoving a 40 kg crate with 250 N while the floor drags back with 80 N of friction is not accelerating it at 250/40 = 6.25 m/s². The crate feels 250 − 80 = 170 N, and accelerates at 4.25 m/s². Draw the body on its own, put every arrow that touches it on the sketch, add the ones pointing forward, subtract the ones pointing back, and what is left is the only force the second law wants to hear about.

Three answers come out of that subtraction and all three mean something. A positive result is the ordinary case: the body speeds up along F₁. Zero does not mean stationary — it means not accelerating, which for something already moving is Newton's first law and constant velocity: a car at a steady 100 km/h has its full engine thrust exactly cancelled by drag and rolling resistance, and a skydiver at terminal velocity is falling fast with no net force at all. A negative result means the opposing side is winning and the body is decelerating, or accelerating backwards, which is precisely what a brake pedal and a headwind both do. The restriction worth remembering is that this is one axis: forces at an angle must be resolved into components first, and only then do they belong in this sum.

Net Force on One Body
Fnet=F1−F2F_{\text{net}} = F_1 - F_2
Where
  • FnetF_{\text{net}}= Net force (N)
  • F1F_1= Force along the motion (N)
  • F2F_2= Force opposing the motion (N)
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