NCERT Notes Class 9 Science Chapter 6 How Forces Affect Motion

The NCERT Notes Class 9 Science Chapter 6 How Forces Affect Motion give you a quick, clear revision of the whole chapter from the new Exploration textbook. In one place you get every key idea: what a force does, how to find the net force, the difference between balanced and unbalanced forces, and Newton's three laws of motion. The notes use short lines, simple words, and the main formula F = ma, so you can revise the full chapter fast before a class test or the 2026-27 exam.

• Full concept revision: force, net force, balanced and unbalanced forces, friction, and Newton's three laws of motion in one set of notes.
• Formula ready: Newton's second law F = ma with units, plus quick force-diagram tips for numericals.
• Why it matters: Chapter 6 is the base for work, energy, and later CBSE, JEE, and NEET physics.

What You Revise in Class 9 Science Chapter 6 How Forces Affect Motion

A force is a push or a pull. Chapter 6 explains how a force changes the way an object moves. The NCERT Notes Class 9 Science Chapter 6 How Forces Affect Motion cover every idea in the order the Exploration book uses, so your revision follows the same flow as the chapter.

These notes help you recall the core points in minutes:

• Force and its effects: a force can start motion, stop it, change speed or direction, or change an object's shape.
• Net force: add forces in the same direction, subtract forces in opposite directions.
• Balanced and unbalanced forces: zero net force keeps velocity constant, a leftover force causes acceleration.
• Newton's three laws: inertia, F = ma, and action-reaction pairs.

How Forces Affect Motion Class 9 Science Explained in One Shot

Source: Alakh Pandey - Class 9th & 10th on YouTube

Force and Its Effects: Quick Revision Notes

Force is the central idea of the whole chapter, so start your revision here. A force is any push or pull that one object applies on another. It is a vector, which means you must state both its size (magnitude) and its direction.

• SI unit: the newton, written with a small letter and the symbol N.
• What a force can do: move an object from rest, speed it up, slow it down, change its direction, or change its shape.
• Measuring a force: a spring balance measures the pull on an object, such as its weight.

Because force has direction, two forces on the same object can either help each other or work against each other. That single idea leads straight to the net force and to balanced and unbalanced forces.

Balanced and Unbalanced Forces in Class 9 Science Chapter 6

This is one of the most tested ideas in the chapter, so revise it well. When the forces on an object add up to zero, they are balanced. When one force is left over, they are unbalanced, and that leftover force changes the motion.

Remember one common trap: an object moving at constant velocity has zero net force, not no force. A steady push can still act, but friction cancels it exactly, so the forces stay balanced.

Newton's Three Laws of Motion Notes for Class 9

Most of Chapter 6 comes back to three simple rules. Learn them well and the rest of the chapter becomes easy to recall.

• First law: explains why you jerk forward when a bus stops suddenly. Your body wants to keep moving.
• Second law: the workhorse of the chapter. If you know any two of force, mass, and acceleration, you can find the third.
• Third law: explains why a boat moves back when a sailor jumps forward, and why a gun recoils.

Key Formulas in How Forces Affect Motion Class 9 Science

Keep these formulas ready for the numericals in the Revise, Reflect, Refine exercise. Each one comes straight from the ideas in Chapter 6.

• Newton's second law: F = ma, where F is net force in newtons, m is mass in kilograms, and a is acceleration in m s^-2.
• Acceleration: a = v - ut, found as the slope of a velocity-time graph.
• Net force on a line: F_net = (sum of forward forces) − (sum of backward forces).

For a graph question, first read the acceleration as the slope, then put it into F = ma. This one link solves most of the numericals in the chapter, from a moving trolley to a braking car.

Friction and Everyday Force Examples in Chapter 6

Friction appears in many parts of this chapter, so it is worth a short revision of its own. Friction is a contact force that always acts opposite to the direction of motion, or attempted motion, between two surfaces.

• Friction lets you walk, write, and stop a moving cycle, so it is often helpful, not just a nuisance.
• When a box moves at constant velocity, the push you apply is exactly balanced by friction.
• Smooth or "frictionless" surfaces are used in problems to keep the focus on the applied force alone.

Everyday examples make the ideas stick: a seat belt uses Newton's first law, rowing a boat uses the third law, and pushing a loaded trolley uses the second law. Linking each law to a real action is the fastest way to revise Chapter 6.

Common Mistakes and Quick Revision Tips for Forces and Motion

Most lost marks in this chapter come from small slips, not hard ideas. Fix these while you revise and your answers stay clean.

• Adding forces that point in opposite directions instead of subtracting them.
• Treating action and reaction as forces on the same object, so they seem to cancel.
• Forgetting that acceleration points in the same direction as the net force.
• Mixing up mass (in kilograms) with weight (a force, in newtons).

How Collegedunia Notes Help You Revise Forces and Motion

Collegedunia gives you the full NCERT Notes Class 9 Science Chapter 6 How Forces Affect Motion as clean, short, easy-to-read revision in one place.

• 2026-27 Exploration match: every note follows the new textbook and the Revise, Reflect, Refine flow.
• Simple English: short lines and everyday words, so a Class 9 student can revise without help.
• Formula and table ready: F = ma, Newton's laws, and the balanced versus unbalanced table in one view.
• Free PDF: download the notes and revise offline before your exam.

More How Forces Affect Motion Class 9 Science Resources

NCERT Notes for Class 9 Science: All Chapters

Use the table below to open the NCERT Notes for any other chapter of the new Class 9 Science Exploration book.