1. What Are Balanced and Unbalanced Forces?
When more than one force acts on an object, the effect depends on how strong the forces are and in which direction they act. These forces can either cancel each other or change the motion of the object.
This leads to two types of combined forces: balanced and unbalanced forces.
1.1. Why Forces Need to Be Compared
A single force acting alone is easy to understand. But when multiple forces act at the same time, we look at the net force — the total effect of all forces combined.
Net force decides if an object will stay at rest, keep moving, or change its motion.
2. Balanced Forces
Balanced forces are forces that are equal in magnitude but act in opposite directions. Because they cancel each other, the net force becomes zero.
2.1. Effect of Balanced Forces
Balanced forces cannot change the state of motion. They cannot start or stop an object. They also cannot change speed or direction.
An object under balanced forces:
- remains at rest, or
- continues moving with the same speed in a straight line.
2.2. Examples of Balanced Forces
- A book resting on a table. The table pushes upward with the same force that gravity pulls downward.
- A person standing still. Upward force from the ground balances downward weight.
- Tug-of-war teams pulling equally — the rope does not move.
3. Unbalanced Forces
Unbalanced forces do not cancel each other. Their magnitudes are unequal or they act in different directions. As a result, the net force is not zero.
3.1. Effect of Unbalanced Forces
Unbalanced forces can:
- start motion
- stop motion
- speed up or slow down an object
- change the direction of motion
Simply put, unbalanced forces cause acceleration.
3.2. Examples of Unbalanced Forces
- A moving bicycle slowing down due to friction.
- A football changing direction when kicked.
- A trolley beginning to move when pushed with a greater force than friction.
- Tug-of-war: if one team pulls harder, the rope moves in that direction.
4. How to Find the Net Force
To know whether the forces are balanced or unbalanced, we calculate the net force acting on the object.
4.1. Same Direction
If forces act in the same direction, we add them:
\( F_{net} = F_1 + F_2 \)
Example: A 5 N force and a 3 N force in the same direction give a net force of 8 N.
4.2. Opposite Directions
If forces act in opposite directions, we subtract them:
\( F_{net} = |F_1 - F_2| \)
Example: A 10 N push right and a 6 N push left give a net force of 4 N right.
4.3. Net Force = 0 → Balanced
If the final result is zero, forces are balanced. If not, they are unbalanced.
5. Real-Life Situations Using Balanced and Unbalanced Forces
Understanding balanced and unbalanced forces helps explain many common actions.
5.1. When Forces Are Balanced
- A picture hanging on a nail remains still.
- A book on a shelf remains unmoved.
5.2. When Forces Become Unbalanced
- A person pushes a shopping cart harder to make it move.
- A ball slows down due to friction acting opposite its motion.
- Strong wind pushes a door open.