Drag the force arrows on an object and the net force updates live, with a balanced-or-unbalanced verdict. Build free-body diagrams and find when an object accelerates.
UNBALANCED
Net force = 3 N right
The forces do not cancel, so the object accelerates in the direction of the net force.
Horizontal: 6 - 3 = 3 N
Vertical: 5 - 5 = 0 N
Net force 3 newtons. Unbalanced right, the object accelerates.
What is the net force?
Almost everything has several forces acting on it at once: gravity pulling down, a
surface pushing up, a hand pushing, friction resisting. The net force is what you get
when you add all of those up as vectors (direction matters). It is the net force, not
any single force, that decides whether an object speeds up, slows down, or stays as it is.
Drag the arrows in the builder above and watch the net force and the verdict change.
Balanced vs unbalanced forces
Balanced forces cancel out: the net force is zero. The object does not
accelerate, so it stays at rest or keeps moving at a constant velocity.
Unbalanced forces do not cancel: there is a net force, and the object
accelerates in that direction.
The most common trap: balanced does not mean stopped
A balanced object can be moving. A car cruising at a steady 60 km/h has balanced
forces (engine push cancels friction and drag), yet it is clearly moving. “Balanced”
means the velocity is not changing, not that the object is stopped.
How to draw a free-body diagram
A free-body diagram shows every force acting on one object as an arrow:
Weight (gravity): always points down.
Normal force: a surface pushing perpendicular to itself (up, from a flat table).
Applied force: a push or pull you supply.
Friction: opposes sliding, so it points against the motion.
Only draw forces acting on the object. A classic mistake is inventing a “force of
motion” in the direction of travel: there is no such force, a moving object needs no
forward force to keep going (that is Newton’s first law).
Finding the net force
Add along each line: horizontally, applied minus friction; vertically, normal minus
weight. The readout does exactly this. Whatever is left over, combined, is the net force,
and by Newton’s second law that net force divided by
mass is the acceleration.
Using this with a class
Give a scenario (“a sled pushed across snow”, “a lamp hanging from a cord”) and have
students set the arrows to match, predict balanced or unbalanced, then check the verdict.
It is free to embed on your own site or LMS.
Frequently asked questions
What is net force?
Net force is the single force you get by adding up all the forces acting on an object, taking direction into account (a vector sum). It is measured in newtons (N) and always has a direction. If the forces cancel, the net force is zero; if they do not, the net force points in some direction and the object accelerates that way.
What is the difference between balanced and unbalanced forces?
Forces are balanced when they cancel out, giving a net force of zero. A balanced object stays at rest OR keeps moving at constant velocity, it does not accelerate. Forces are unbalanced when they do not cancel, giving a non-zero net force, and an unbalanced net force always causes acceleration (a change in speed or direction) in the direction of the net force.
How do you find the net force?
Add the forces as vectors. Along one line, add forces in one direction and subtract those in the opposite direction (for example applied force minus friction). Do the same vertically (normal force minus weight). The leftover amount in each direction, combined, is the net force. If everything cancels, the net force is zero and the forces are balanced.
How do you draw a free-body diagram?
Represent the object as a dot or box, then draw an arrow for every force acting ON it, pointing in the force's direction with a length showing its size. Common forces are the applied force, weight (gravity, always down), the normal force (a surface pushing perpendicular to itself), friction (opposing sliding), and tension. Only include forces on the object itself, never a made-up 'force of motion'.
Does a balanced force mean the object is not moving?
No. Balanced forces (net force zero) mean no acceleration, but the object can still be moving at a steady velocity. A car cruising at a constant 60 km/h on a straight road has balanced forces, the engine's push exactly cancels friction and air resistance, yet it is clearly moving. Balanced means 'velocity is not changing', not 'stopped'.