What is an Unbalanced Force?

S4-SA1-0260

Grade Level:

Class 6

Space Technology, EVs, Climate Change, Biotechnology, HealthTech, Robotics, Chemistry, Physics

Definition

What is it?

An unbalanced force is a force that causes a change in an object's motion. When forces acting on an object are not equal and opposite, they are unbalanced, leading to movement or a change in speed/direction.

Simple Example

Quick Example

Imagine you and your friend are pushing a heavy school desk. If you push with more strength (force) than your friend, the desk will move in your direction. This happens because your combined forces are unbalanced, causing the desk to shift.

Worked Example

Step-by-Step

Let's say a cricket ball is sitting still on the ground. You kick it.

Step 1: The ball is initially at rest, meaning the forces on it are balanced (gravity pulling down, ground pushing up).
---Step 2: You apply a force of 10 Newtons (N) with your foot in one direction.
---Step 3: There might be a small opposing force like air resistance, say 1 N.
---Step 4: The net force on the ball is 10 N - 1 N = 9 N in the direction of your kick.
---Step 5: Since there is a net force of 9 N, the forces are unbalanced.
---Step 6: This unbalanced force causes the cricket ball to move and gain speed.

Answer: The ball moves because the 9 N net force is unbalanced.

Why It Matters

Understanding unbalanced forces is key to designing everything from space rockets by ISRO to electric vehicles and even robotic arms. Engineers and scientists use this concept to predict and control how things move, helping build faster cars or safer structures.

Common Mistakes

MISTAKE: Thinking an object needs an unbalanced force to stay in motion. | CORRECTION: An unbalanced force is needed to START moving, STOP moving, or CHANGE speed/direction. Once an object is moving at a constant speed in a straight line, the forces on it are balanced.

MISTAKE: Believing that if multiple forces act on an object, they are automatically unbalanced. | CORRECTION: Multiple forces can act on an object and still be balanced if their combined effect cancels each other out, resulting in no change in motion.

MISTAKE: Confusing an unbalanced force with a 'strong' force. | CORRECTION: An unbalanced force simply means the net force is not zero. Even a very small net force can be unbalanced and cause motion, given enough time.

Practice Questions

Try It Yourself

QUESTION: If a book is lying still on a table, are the forces acting on it balanced or unbalanced? | ANSWER: Balanced

QUESTION: Two friends are playing tug-of-war. Friend A pulls with 50 N force, and Friend B pulls with 45 N force in the opposite direction. What is the net force and is it balanced or unbalanced? | ANSWER: Net force is 5 N towards Friend A. It is unbalanced.

QUESTION: A car is speeding up on a highway. Are the forces acting on the car balanced or unbalanced? Explain why. | ANSWER: Unbalanced. Because the car is speeding up (changing its motion), there must be a net force acting on it in the direction of its movement, making the forces unbalanced.

MCQ

Quick Quiz

What happens to an object when an unbalanced force acts upon it?

It remains at rest.

It moves at a constant speed in a straight line.

Its motion changes (starts, stops, speeds up, slows down, or changes direction).

It disappears.

The Correct Answer Is:

An unbalanced force always causes a change in an object's motion. If forces are balanced, the object either stays at rest or moves at a constant speed and direction.

Real World Connection

In the Real World

When a delivery bike rider from Zomato or Swiggy applies brakes, they create an unbalanced force opposite to the bike's motion, causing it to slow down and stop. Similarly, when a rocket launches from Sriharikota, the massive thrust it generates creates an unbalanced force that pushes it upwards against gravity.

Key Vocabulary

Key Terms

FORCE: A push or a pull that can change an object's motion | BALANCED FORCE: Forces that are equal in magnitude and opposite in direction, resulting in no change in motion | NET FORCE: The overall force acting on an object, considering all individual forces | MOTION: The action or process of moving or being moved

What's Next

What to Learn Next

Now that you understand unbalanced forces, you're ready to learn about 'Newton's Laws of Motion'. These laws explain exactly how unbalanced forces affect an object's movement, building directly on what you've learned here.