medium difficulty5 min

Balanced and Unbalanced Forces

Balanced forces have zero net force and do not change the state of motion, while unbalanced forces have non-zero net force and can change motion.

In one line: Balanced means force present, effect cancelled.

Practice This Concept

Understand it

When equal forces act in opposite directions on the same object, their effects cancel for motion. If one force is larger, the object accelerates in the direction of the greater net force.

Example

Two students push a box with 50 N each from opposite sides; the box does not move because the forces are balanced.

Rule to remember

Net force = sum of forces with direction.

Equal opposite forces give zero net force.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1A box is pulled right with 70 N and left with 40 N.
2Net force = 70 - 40 = 30 N to the right, so the forces are unbalanced.

Method you can reuse

Mark directions, subtract opposite forces, identify net force direction, then state whether motion changes.

Sketch it in your answer

Draw a block with two equal opposite arrows for balanced forces and unequal opposite arrows for unbalanced forces.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

If two equal opposite forces act on a table and it remains at rest, are forces absent?

Think first, then show answer

No, forces are acting, but they are balanced because their net force is zero, so the table's state of rest does not change.

Common wrong answer

Adding 70 N and 40 N as 110 N is wrong when forces act in opposite directions.

Don't mix this up

Students often say balanced forces mean no force is acting, but actually forces are present and their net effect is zero.

Exam tip

Use the phrase 'net force is zero' for balanced forces and 'net force is non-zero' for unbalanced forces.