What is Force and Net Force?
Force is a push or pull that can change an object's motion, and net force is the combined effect of every force acting on it. Understanding net force is the key to predicting whether an object speeds up, slows down, or stays still.
Force is any push or pull on an object, measured in newtons (N). Net force is the vector sum of all forces acting on an object; if forces are unbalanced, the object accelerates in the direction of the net force.
- •Net force = 0
- •No change in motion
- •Object stays at rest or constant velocity
- •Example: a book resting on a table
- •Net force ≠ 0
- •Object accelerates
- •Speed or direction changes
- •Example: pushing a stalled car
Try it: interactive calculator
Step-by-step worked examples
Two people pull a rope in opposite directions with forces of 80 N and 50 N. Find the net force and its direction.
Net force = 80 − 50 = 30 N Direction: toward the stronger pull (80 N side)
A box on a table has a weight of 20 N pulling down and a normal force of 20 N pushing up. Find the net force.
Net force = 20 − 20 = 0 N Forces are balanced → the box stays at rest
Three forces act on a sled: 40 N forward, 15 N backward (friction), 5 N backward (air resistance). Find the net force.
Backward forces = 15 + 5 = 20 N Net force = 40 − 20 = 20 N forward
Flashcards
Quick quiz
Q1.Two forces of 30 N and 10 N act in the same direction. What is the net force?
Q2.A net force of zero means the object is...
Q3.What is the SI unit of force?
Q4.A 50N force pushes right and a 20N force pushes left on a box. What is the net force?
The full card deck, worked steps and AI-tutor support for “What is Force and Net Force?” are in Notek — study by hand before your exam.
Common mistakes
Force and net force are the same thing. — Correct: Force is a single push/pull; net force is the sum of all forces acting on an object.
If two forces act on an object, it must be moving. — Correct: Balanced forces can produce zero net force, keeping the object at rest.
Net force is just adding numbers, ignoring direction. — Correct: Force is a vector — direction matters, so opposing forces subtract.
Zero net force means no forces are acting. — Correct: Zero net force can still have several forces acting, canceling each other out.
FAQ
What is net force?
Net force is the vector sum of all forces acting on an object; it determines whether and how the object accelerates.
What is the net force formula?
F_net = ΣF, the sum of all individual forces, taking direction into account.
What are examples of net force?
A tug-of-war, a car accelerating because engine force is stronger than friction, or a book resting in equilibrium on a table.
How to calculate net force?
Add forces acting in the same direction, subtract forces acting in opposite directions, then apply Newton's second law F = ma if needed.